VxWorks Kernel Programmer's Guide, 6.6 Programmers Guide
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VxWorks Kernel Programmer's Guide, 6.6 VxWorks ® KERNEL PROGRAMMER'S GUIDE 6.6 Copyright © 2007 Wind River Systems, Inc. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means without the prior written permission of Wind River Systems, Inc. Wind River, Tornado, and VxWorks are registered trademarks of Wind River Systems, Inc. The Wind River logo is a trademark of Wind River Systems, Inc. Any third-party trademarks referenced are the property of their respective owners. For further information regarding Wind River trademarks, please see: http://www.windriver.com/company/terms/trademark.html This product may include software licensed to Wind River by third parties. Relevant notices (if any) are provided in your product installation at the following location: installDir/product_name/3rd_party_licensor_notice.pdf. Wind River may refer to third-party documentation by listing publications or providing links to third-party Web sites for informational purposes. Wind River accepts no responsibility for the information provided in such third-party documentation. Corporate Headquarters Wind River Systems, Inc. 500 Wind River Way Alameda, CA 94501-1153 U.S.A. toll free (U.S.): (800) 545-WIND telephone: (510) 748-4100 facsimile: (510) 749-2010 For additional contact information, please visit the Wind River URL: http://www.windriver.com For information on how to contact Customer Support, please visit the following URL: http://www.windriver.com/support VxWorks Kernel Programmer's Guide, 6.6 14 Nov 07 Part #: DOC-16075-ND-00 Contents PART I: CORE TECHNOLOGIES 1 2 Overview ............................................................................................... 3 1.1 Introduction ............................................................................................................. 3 1.2 Related Documentation Resources ..................................................................... 4 1.3 VxWorks Configuration and Build ..................................................................... 5 Kernel .................................................................................................... 7 2.1 Introduction ............................................................................................................. 7 2.2 Kernel Architecture ................................................................................................ 9 2.2.1 Operating System Facilities .................................................................... 10 2.2.2 System Tasks ............................................................................................. 11 2.3 System Startup ........................................................................................................ 13 2.4 VxWorks Configuration ........................................................................................ 14 2.4.1 VxWorks Image Types ............................................................................ 15 2.4.2 VxWorks Components ............................................................................ 17 2.4.3 Device Driver Selection ........................................................................... 22 iii VxWorks Kernel Programmer's Guide, 6.6 2.4.4 VxWorks Configuration Profiles ............................................................ 22 2.4.5 Small VxWorks Configuration Profiles ................................................ 24 How Small Configuration Profiles Create Smaller Systems .............. Configuring and Building Small VxWorks Configurations ............... Optimization of Small VxWorks Profile Systems ................................ Minimal Kernel Profile ............................................................................ Basic Kernel Profile .................................................................................. Basic OS Profile ......................................................................................... 25 27 27 28 33 35 Customizing VxWorks Code .................................................................. 39 System Clock Modification ..................................................................... Hardware Initialization Customization ................................................ Other Customization ............................................................................... 39 39 39 Power Management ............................................................................................... 40 2.5.1 Power Management for IA Architecture .............................................. 41 ACPI Processor Power and Performance States .................................. ACPI Thermal Management ................................................................... VxWorks Power Management Facilities ............................................... Configuring VxWorks With Power Management Facilities .............. Power Management and System Performance .................................... 41 43 43 49 49 Power Management for Other Architectures ....................................... 49 Kernel Applications ............................................................................................... 51 2.6.1 C and C++ Libraries ................................................................................. 52 2.6.2 Application Structure .............................................................................. 52 2.6.3 VxWorks Header Files ............................................................................. 53 2.6.4 Static Instantiation of Kernel Objects .................................................... 56 2.6.5 Applications and VxWorks Kernel Component Requirements ........ 62 2.6.6 Building Kernel Application Modules .................................................. 62 2.6.7 Downloading Kernel Application Object Modules to a Target ......... 64 2.6.8 Linking Kernel Application Object Modules with VxWorks ............ 64 2.6.9 Image Size Considerations ...................................................................... 65 2.6.10 Configuring VxWorks to Run Applications Automatically .............. 66 2.4.6 2.5 2.5.2 2.6 iv Contents 2.7 Custom Kernel Libraries ....................................................................................... 67 2.8 Custom VxWorks Components and CDFs ........................................................ 67 2.8.1 Creating and Modifying Components .................................................. 68 Defining a Component ............................................................................ Modifying a Component ......................................................................... 68 74 2.8.2 CDF Precedence and CDF Installation .................................................. 75 2.8.3 Testing New Components ...................................................................... 78 2.8.4 Component Description Language ....................................................... 79 2.8.5 CDF Naming Conventions ..................................................................... 80 2.8.6 Component CDF Object .......................................................................... 81 Component Properties ............................................................................ Component Template .............................................................................. 82 85 Parameter CDF Object ............................................................................. 87 Parameter Properties ............................................................................... Parameter Template ................................................................................. 87 88 Initialization Group CDF Object ............................................................ 88 Initialization Group Properties .............................................................. Initialization Group Template ................................................................ 89 90 Bundle CDF Object ................................................................................... 90 Bundle Properties ..................................................................................... 90 Profile CDF Object ................................................................................... 91 Profile Properties ...................................................................................... Profile Template ....................................................................................... 91 91 Folder CDF Object .................................................................................... 92 Folder Properties ...................................................................................... Folder Template ....................................................................................... 93 94 Selection CDF Object ............................................................................... 94 Selection Properties .................................................................................. Selection Template ................................................................................... 95 95 CDF Template ........................................................................................... 96 2.8.7 2.8.8 2.8.9 2.8.10 2.8.11 2.8.12 2.8.13 v VxWorks Kernel Programmer's Guide, 6.6 2.9 Custom System Calls ............................................................................................. 100 2.9.1 How System Calls Work ......................................................................... 100 2.9.2 System Call Requirements ...................................................................... 101 System Call Naming Rules ..................................................................... System Call Numbering Rules ............................................................... System Call Argument Rules .................................................................. System Call Return Value Rules ............................................................ 2.9.3 101 102 103 104 System Call Handler Requirements ...................................................... 105 System Call Handler Naming Rules ...................................................... 106 System Call Handler Argument Validation ......................................... 106 System Call Handler Error Reporting ................................................... 107 2.9.4 Adding System Calls ............................................................................... 107 Adding System Calls Statically .............................................................. 107 Adding System Calls Dynamically ........................................................ 112 2.10 2.9.5 Monitoring And Debugging System Calls ........................................... 114 2.9.6 Documenting Custom System Calls ...................................................... 116 Custom Scheduler .................................................................................................. 118 2.10.1 Requirements for a Custom Scheduler ................................................. 118 Code Requirements .................................................................................. 118 Configuration Requirements .................................................................. 121 2.10.2 Traditional VxWorks Scheduler ............................................................. 123 Scheduler Initialization ............................................................................ 123 Multi-way Queue Structure .................................................................... 124 Q_CLASS Operators ................................................................................ 126 3 Boot Loader .......................................................................................... 131 3.1 Introduction ............................................................................................................. 132 3.2 Using a Default Boot Loader ................................................................................ 132 3.3 Boot Loader Image Types ..................................................................................... 133 3.4 Boot Loader Shell ................................................................................................... 135 vi Contents 3.4.1 3.5 Boot Loader Shell Commands ................................................................ 136 Boot Loader Parameters ......................................................................................... 140 3.5.1 Displaying Current Boot Parameters .................................................... 140 3.5.2 Description of Boot Loader Parameters ................................................ 141 3.5.3 Changing Boot Loader Parameters Interactively ................................ 144 3.6 Rebooting VxWorks ............................................................................................... 145 3.7 Customizing and Building Boot Loaders .......................................................... 146 3.7.1 Configuring Boot Loaders ....................................................................... 146 3.7.2 Boot Loader Components ....................................................................... 146 3.7.3 Configuring Boot Loader Parameters Statically .................................. 147 3.7.4 Enabling Networking for Non-Boot Interfaces .................................... 148 3.7.5 Selecting a Boot Device ............................................................................ 148 3.7.6 Reconfiguring Memory ........................................................................... 149 Persistent Memory Region ...................................................................... 150 3.7.7 4 Building Boot Loaders ............................................................................. 151 3.8 Installing Boot Loaders ......................................................................................... 152 3.9 Booting From a Network ...................................................................................... 152 3.10 Booting From a Target File System .................................................................... 154 3.11 Booting From the Host File System Using TSFS ............................................. 155 Multitasking .......................................................................................... 157 4.1 Introduction ............................................................................................................. 159 4.2 Tasks and Multitasking ....................................................................................... 160 4.2.1 Task States and Transitions .................................................................... 161 vii VxWorks Kernel Programmer's Guide, 6.6 4.3 Task Scheduling ..................................................................................................... 166 4.3.1 Task Priorities ........................................................................................... 166 4.3.2 Task Scheduling Control ......................................................................... 167 Task Priority .............................................................................................. 167 Preemption Locks ..................................................................................... 167 4.3.3 VxWorks Traditional Scheduler ............................................................. 168 Priority-Based Preemptive Scheduling ................................................. 169 Round-Robin Scheduling ........................................................................ 169 4.4 Task Creation and Management ......................................................................... 171 4.4.1 Task Creation and Activation ................................................................. 172 4.4.2 Task Creation Options ............................................................................. 173 4.4.3 Task Stack .................................................................................................. 175 Task Stack Protection ............................................................................... 176 4.5 4.4.4 Task Names and IDs ................................................................................ 177 4.4.5 Task Information ...................................................................................... 179 4.4.6 Task Deletion and Deletion Safety ......................................................... 180 4.4.7 Task Execution Control ........................................................................... 181 4.4.8 Tasking Extensions ................................................................................... 182 Task Error Status: errno ......................................................................................... 184 4.5.1 Layered Definitions of errno .................................................................. 185 4.5.2 A Separate errno Value for Each Task .................................................. 185 4.5.3 Error Return Convention ........................................................................ 186 4.5.4 Assignment of Error Status Values ........................................................ 186 4.6 Task Exception Handling ...................................................................................... 187 4.7 Shared Code and Reentrancy ............................................................................... 187 4.7.1 Dynamic Stack Variables ......................................................................... 189 4.7.2 Guarded Global and Static Variables .................................................... 190 4.7.3 Task-Specific Variables ........................................................................... 190 viii Contents Thread-Local Variables: __thread Storage Class ................................. 190 taskVarLib and Task Variables .............................................................. 191 4.7.4 Multiple Tasks with the Same Main Routine ....................................... 192 4.8 Intertask and Interprocess Communication ...................................................... 193 4.9 Public and Private Objects ................................................................................... 194 4.9.1 Creating and Naming Public and Private Objects .............................. 194 4.9.2 Object Ownership and Resource Reclamation ..................................... 195 4.10 Shared Data Structures .......................................................................................... 196 4.11 Mutual Exclusion .................................................................................................... 196 4.12 4.11.1 Interrupt Locks and Latency .................................................................. 197 4.11.2 Preemptive Locks and Latency .............................................................. 197 Semaphores ............................................................................................................. 198 4.12.1 Semaphore Control .................................................................................. 200 Static Instantiation of Semaphores ........................................................ 201 4.12.2 Binary Semaphores .................................................................................. 201 Mutual Exclusion ..................................................................................... 203 Synchronization ........................................................................................ 203 4.12.3 Mutual-Exclusion Semaphores .............................................................. 205 Priority Inversion ..................................................................................... 205 Deletion Safety .......................................................................................... 207 Recursive Resource Access ..................................................................... 207 4.12.4 Counting Semaphores ............................................................................. 208 4.12.5 Read/Write Semaphores ........................................................................ 209 Specification of Read or Write Mode .................................................... 210 Precedence for Write Access Operations .............................................. 211 Read/Write Semaphores and System Performance ........................... 211 4.12.6 Special Semaphore Options .................................................................... 211 Timeouts .................................................................................................... 212 Queues ....................................................................................................... 212 ix VxWorks Kernel Programmer's Guide, 6.6 4.12.7 4.13 Semaphores and VxWorks Events ......................................................... 213 Message Queues ..................................................................................................... 213 4.13.1 VxWorks Message Queue Routines ...................................................... 215 4.13.2 Displaying Message Queue Attributes ................................................. 217 4.13.3 Servers and Clients with Message Queues ........................................... 217 4.13.4 Message Queues and VxWorks Events ................................................. 218 4.14 Pipes .......................................................................................................................... 218 4.15 VxWorks Events ...................................................................................................... 219 4.15.1 Preparing a Task to Receive Events ....................................................... 220 4.15.2 Sending Events to a Task ........................................................................ 221 4.15.3 Accessing Event Flags .............................................................................. 223 4.15.4 Events Routines ........................................................................................ 224 4.15.5 Task Events Register ................................................................................ 224 4.15.6 Show Routines and Events ..................................................................... 225 4.16 Message Channels ................................................................................................. 226 4.17 Network Communication ..................................................................................... 226 4.18 Signals ..................................................................................................................... 226 4.18.1 Configuring VxWorks for Signals ......................................................... 228 4.18.2 Basic Signal Routines ............................................................................... 229 4.18.3 Queued Signal Routines ......................................................................... 230 4.18.4 Signal Events ............................................................................................. 236 4.18.5 Signal Handlers ........................................................................................ 236 4.19 Watchdog Timers ................................................................................................... 239 4.20 Interrupt Service Routines .................................................................................... 241 4.20.1 x Connecting Routines to Interrupts ........................................................ 242 Contents 4.20.2 Interrupt Stack .......................................................................................... 242 Filling Interrupt Stacks ............................................................................ 243 Interrupt Stack Protection ....................................................................... 243 5 4.20.3 Writing and Debugging ISRs .................................................................. 244 4.20.4 ISRs and the Kernel Work Queue .......................................................... 244 4.20.5 Special Limitations of ISRs ...................................................................... 245 4.20.6 Exceptions at Interrupt Level ................................................................. 248 4.20.7 Reserving High Interrupt Levels ........................................................... 248 4.20.8 Additional Restrictions for ISRs at High Interrupt Levels ................. 249 4.20.9 Interrupt-to-Task Communication ........................................................ 249 POSIX Facilities .................................................................................... 251 5.1 Introduction ............................................................................................................. 252 5.2 Configuring VxWorks with POSIX Facilities ................................................... 253 5.2.1 VxWorks Components for POSIX Facilities ......................................... 253 5.3 General POSIX Support ........................................................................................ 255 5.4 POSIX Header Files ............................................................................................... 257 5.5 POSIX Namespace .................................................................................................. 259 5.6 POSIX Clocks and Timers .................................................................................... 259 5.7 POSIX Asynchronous I/O ..................................................................................... 263 5.8 POSIX Advisory File Locking .............................................................................. 263 5.9 POSIX Page-Locking Interface ............................................................................ 264 5.10 POSIX Threads ........................................................................................................ 264 5.10.1 POSIX Thread Attributes ........................................................................ 265 5.10.2 VxWorks-Specific Pthread Attributes ................................................... 265 5.10.3 Specifying Attributes when Creating Pthreads ................................... 266 xi VxWorks Kernel Programmer's Guide, 6.6 5.11 5.10.4 POSIX Thread Creation and Management ........................................... 268 5.10.5 POSIX Thread Attribute Access ............................................................. 269 5.10.6 POSIX Thread Private Data .................................................................... 270 5.10.7 POSIX Thread Cancellation .................................................................... 270 POSIX Thread Mutexes and Condition Variables ........................................... 273 5.11.1 Thread Mutexes ........................................................................................ 273 Protocol Mutex Attribute ........................................................................ 274 Priority Ceiling Mutex Attribute ............................................................ 275 5.11.2 5.12 5.13 5.14 Condition Variables ................................................................................. 275 POSIX and VxWorks Scheduling ........................................................................ 277 5.12.1 Differences in POSIX and VxWorks Scheduling ................................. 279 5.12.2 POSIX and VxWorks Priority Numbering ........................................... 279 5.12.3 Default Scheduling Policy ....................................................................... 280 5.12.4 VxWorks Traditional Scheduler ............................................................. 281 5.12.5 POSIX Threads Scheduler ....................................................................... 282 5.12.6 POSIX Scheduling Routines .................................................................... 286 5.12.7 Getting Scheduling Parameters: Priority Limits and Time Slice ....... 287 POSIX Semaphores ................................................................................................ 289 5.13.1 Comparison of POSIX and VxWorks Semaphores .............................. 290 5.13.2 Using Unnamed Semaphores ................................................................. 291 5.13.3 Using Named Semaphores ..................................................................... 294 POSIX Message Queues ........................................................................................ 299 5.14.1 Comparison of POSIX and VxWorks Message Queues ...................... 300 5.14.2 POSIX Message Queue Attributes ......................................................... 300 5.14.3 Displaying Message Queue Attributes ................................................. 303 5.14.4 Communicating Through a Message Queue ....................................... 303 5.14.5 Notification of Message Arrival ............................................................ 307 xii Contents 6 5.15 POSIX Signals ......................................................................................................... 313 5.16 POSIX Memory Management .............................................................................. 313 Memory Management .......................................................................... 315 6.1 Introduction ............................................................................................................. 316 6.2 Configuring VxWorks With Memory Management Facilities ...................... 317 6.3 System Memory Maps ........................................................................................... 317 6.3.1 System Memory Map Without Process Support ................................. 318 6.3.2 System Memory Map with Process Support ........................................ 321 6.3.3 System Memory Map with Processes Running ................................... 323 6.4 Shell Commands .................................................................................................... 327 6.5 System RAM Autosizing ...................................................................................... 327 6.6 Reserved Memory .................................................................................................. 328 6.7 Kernel Heap and Memory Partition Management .......................................... 329 6.8 6.9 6.7.1 Configuring the Kernel Heap and the Memory Partition Manager . 329 6.7.2 Basic Heap and Memory Partition Manager ........................................ 330 6.7.3 Full Heap and Memory Partition Manager .......................................... 330 Memory Error Detection ....................................................................................... 331 6.8.1 Heap and Partition Memory Instrumentation ..................................... 331 6.8.2 Compiler Instrumentation ...................................................................... 338 Virtual Memory Management ............................................................................. 343 6.9.1 Configuring Virtual Memory Management ......................................... 344 xiii VxWorks Kernel Programmer's Guide, 6.6 6.9.2 Managing Virtual Memory Programmatically .................................... 346 Modifying Page States ............................................................................. Making Memory Non-Writable ............................................................. Invalidating Memory Pages .................................................................... Locking TLB Entries ................................................................................. Page Size Optimization ........................................................................... Setting Page States in ISRs ...................................................................... 6.9.3 6.10 6.11 346 348 350 350 351 351 Troubleshooting ....................................................................................... 352 Additional Memory Protection Features ........................................................... 353 6.10.1 Configuring VxWorks for Additional Memory Protection ................ 354 6.10.2 Stack Overrun and Underrun Detection ............................................... 354 6.10.3 Non-Executable Task Stack ..................................................................... 355 6.10.4 Text Segment Write Protection ............................................................... 355 6.10.5 Exception Vector Table Write Protection .............................................. 355 Processes Without MMU Support ....................................................................... 355 Configuring VxWorks With Process Support for Systems Without an MMU ........................................................................................... 356 7 I/O System ............................................................................................. 359 7.1 Introduction ............................................................................................................. 360 7.2 Configuring VxWorks With I/O Facilities ......................................................... 362 7.3 Files, Devices, and Drivers ................................................................................... 363 7.3.1 7.4 Filenames and the Default Device ......................................................... 363 Basic I/O ................................................................................................................... 365 7.4.1 File Descriptors ......................................................................................... 365 File Descriptor Table ................................................................................ 366 7.4.2 Standard Input, Standard Output, and Standard Error ..................... 366 7.4.3 Standard I/O Redirection ....................................................................... 367 Issues with Standard I/O Redirection .................................................. 368 xiv Contents 7.5 7.6 7.7 7.4.4 Open and Close ........................................................................................ 369 7.4.5 Create and Remove .................................................................................. 372 7.4.6 Read and Write ......................................................................................... 372 7.4.7 File Truncation .......................................................................................... 373 7.4.8 I/O Control ............................................................................................... 373 7.4.9 Pending on Multiple File Descriptors with select( ) ............................ 374 7.4.10 POSIX File System Routines ................................................................... 378 Buffered I/O: stdio ................................................................................................. 378 7.5.1 Using stdio ................................................................................................ 379 7.5.2 Standard Input, Standard Output, and Standard Error ..................... 380 Other Formatted I/O .............................................................................................. 380 7.6.1 Special Cases: printf( ), sprintf( ), and sscanf( ) ................................... 380 7.6.2 Additional Routines: printErr( ) and fdprintf( ) .................................. 381 7.6.3 Message Logging ..................................................................................... 381 Asynchronous Input/Output ................................................................................ 381 7.7.1 The POSIX AIO Routines ........................................................................ 382 7.7.2 AIO Control Block .................................................................................... 384 7.7.3 Using AIO .................................................................................................. 385 AIO with Periodic Checks for Completion .......................................... 385 Alternatives for Testing AIO Completion ............................................ 388 7.8 Devices in VxWorks ............................................................................................... 391 7.8.1 Serial I/O Devices: Terminal and Pseudo-Terminal Devices ............ 392 tty Options ................................................................................................. Raw Mode and Line Mode ..................................................................... tty Special Characters .............................................................................. I/O Control Functions ............................................................................. xv 392 393 394 396 VxWorks Kernel Programmer's Guide, 6.6 7.8.2 Pipe Devices .............................................................................................. 396 Creating Pipes ........................................................................................... 397 Writing to Pipes from ISRs ..................................................................... 397 I/O Control Functions ............................................................................. 397 7.8.3 Pseudo I/O Device ................................................................................... 398 I/O Control Functions ............................................................................. 398 7.8.4 Network File System (NFS) Devices ...................................................... 399 Mounting a Remote NFS File System from VxWorks ........................ 399 I/O Control Functions for NFS Clients ................................................. 400 7.8.5 Non-NFS Network Devices .................................................................... 400 Creating Network Devices ...................................................................... 401 I/O Control Functions ............................................................................. 401 7.8.6 Null Devices ............................................................................................. 402 7.8.7 Sockets ........................................................................................................ 402 7.8.8 Extended Block Device Facility: XBD .................................................... 402 XBD Disk Partition Manager .................................................................. 403 XBD Block Device Wrapper .................................................................... 404 XBD TRFS Component ............................................................................ 405 7.8.9 Transaction-Based Reliable File System Facility: TRFS ...................... 405 Configuring VxWorks With TRFS ......................................................... Automatic Instantiation of TRFS ............................................................ Formatting a Device for TRFS ................................................................ Using TRFS in Applications .................................................................... 7.8.10 406 406 406 408 Block Devices ............................................................................................ 410 XBD RAM Disk ......................................................................................... 411 SCSI Drivers .............................................................................................. 412 7.9 Differences Between VxWorks and Host System I/O ..................................... 422 7.10 Internal I/O System Structure .............................................................................. 423 7.10.1 Drivers ....................................................................................................... 426 The Driver Table and Installing Drivers ............................................... 427 Example of Installing a Driver ............................................................... 428 xvi Contents 7.10.2 Devices ....................................................................................................... 429 The Device List and Adding Devices .................................................... 429 Example of Adding Devices ................................................................... 430 Deleting Devices ....................................................................................... 431 7.10.3 File Descriptors ......................................................................................... 435 File Descriptor Table ................................................................................ Example of Opening a File ...................................................................... Example of Reading Data from the File ................................................ Example of Closing a File ........................................................................ Implementing select( ) ............................................................................. Cache Coherency ...................................................................................... 8 435 436 439 441 441 445 7.11 PCMCIA ................................................................................................................... 450 7.12 Peripheral Component Interconnect: PCI ......................................................... 450 Local File Systems ............................................................................... 451 8.1 Introduction ............................................................................................................. 452 8.2 File System Monitor .............................................................................................. 455 Device Insertion Events ........................................................................... 456 XBD Name Mapping Facility ................................................................. 457 8.3 Virtual Root File System: VRFS .......................................................................... 457 8.4 Highly Reliable File System: HRFS .................................................................... 459 8.4.1 Configuring VxWorks for HRFS ............................................................ 459 8.4.2 Configuring HRFS ................................................................................... 460 8.4.3 Creating an HRFS File System .............................................................. 461 Overview of HRFS File System Creation .............................................. 461 HRFS File System Creation Steps .......................................................... 462 8.4.4 HRFS, ATA, and RAM Disk Examples ................................................. 463 8.4.5 Transactional Operations and Commit Policies ................................ 469 8.4.6 Configuring Transaction Points at Runtime ....................................... 471 8.4.7 File Access Time Stamps ......................................................................... 473 xvii VxWorks Kernel Programmer's Guide, 6.6 8.4.8 Maximum Number of Files and Directories ........................................ 473 8.4.9 Working with Directories ........................................................................ 473 Creating Subdirectories ........................................................................... 473 Removing Subdirectories ........................................................................ 474 Reading Directory Entries ....................................................................... 474 8.4.10 Working with Files ................................................................................... 474 File I/O Routines ...................................................................................... 474 File Linking and Unlinking ..................................................................... 475 File Permissions ........................................................................................ 475 8.4.11 Crash Recovery and Volume Consistency ........................................... 475 Crash Recovery ......................................................................................... 475 Consistency Checking .............................................................................. 476 8.4.12 8.5 I/O Control Functions Supported by HRFS ........................................ 476 MS-DOS-Compatible File System: dosFs .......................................................... 478 8.5.1 Configuring VxWorks for dosFs ............................................................ 478 8.5.2 Configuring dosFs ................................................................................... 480 8.5.3 Creating a dosFs File System .................................................................. 482 Overview of dosFs File System Creation .............................................. 482 dosFs File System Creation Steps ........................................................... 482 8.5.4 dosFs, ATA Disk, and RAM Disk Examples ........................................ 486 8.5.5 Working with Volumes and Disks ......................................................... 491 Accessing Volume Configuration Information .................................... 492 Synchronizing Volumes .......................................................................... 492 8.5.6 Working with Directories ........................................................................ 492 Creating Subdirectories ........................................................................... 492 Removing Subdirectories ........................................................................ 493 Reading Directory Entries ....................................................................... 493 8.5.7 Working with Files ................................................................................... 493 File I/O Routines ...................................................................................... 493 File Attributes ........................................................................................... 493 8.5.8 Disk Space Allocation Options ............................................................... 496 Choosing an Allocation Method ............................................................ 496 xviii Contents Using Cluster Group Allocation ............................................................ 497 Using Absolutely Contiguous Allocation ............................................. 497 8.6 8.7 8.8 8.9 8.5.9 Crash Recovery and Volume Consistency ........................................... 499 8.5.10 I/O Control Functions Supported by dosFsLib ................................... 500 8.5.11 Booting from a Local dosFs File System Using SCSI .......................... 503 Raw File System: rawFs ......................................................................................... 505 8.6.1 Configuring VxWorks for rawFs ........................................................... 505 8.6.2 Creating a rawFs File System ................................................................. 506 8.6.3 Mounting rawFs Volumes ...................................................................... 508 8.6.4 rawFs File I/O .......................................................................................... 509 8.6.5 I/O Control Functions Supported by rawFsLib .................................. 509 CD-ROM File System: cdromFs .......................................................................... 510 8.7.1 Configuring VxWorks for cdromFs ....................................................... 511 8.7.2 Creating and Using cdromFs .................................................................. 512 8.7.3 I/O Control Functions Supported by cdromFsLib ............................. 515 8.7.4 Version Numbers ..................................................................................... 516 Read-Only Memory File System: ROMFS ........................................................ 516 8.8.1 Configuring VxWorks with ROMFS ..................................................... 517 8.8.2 Building a System With ROMFS and Files ........................................... 517 8.8.3 Accessing Files in ROMFS ...................................................................... 517 8.8.4 Using ROMFS to Start Applications Automatically ........................... 518 Target Server File System: TSFS ......................................................................... 518 Socket Support .......................................................................................... Error Handling ......................................................................................... Configuring VxWorks for TSFS Use ...................................................... Security Considerations .......................................................................... Using the TSFS to Boot a Target ............................................................. xix 519 520 520 520 521 VxWorks Kernel Programmer's Guide, 6.6 9 Network File System: NFS ................................................................... 523 9.1 Introduction ............................................................................................................ 523 9.2 Configuring VxWorks for an NFS Client .......................................................... 524 Core NFS Client ........................................................................................ NFS Client All ........................................................................................... NFS v2 Client ............................................................................................ NFS v3 Client ............................................................................................ NFS Mount All .......................................................................................... 9.3 Creating an NFS Client ......................................................................................... 529 Exporting File Systems from the Remote NFS Server ........................ Setting Your NFS Client Name, User ID, and Group ID .................... Mounting a Remote File System ............................................................ Using ioctl( ) With Open Files from a Mounted Directory ................ 9.4 530 531 531 534 Configuring VxWorks for an NFS Server .......................................................... 535 NFS Server ................................................................................................. NFS server All ........................................................................................... NFS server V2 ........................................................................................... NFS server V3 ........................................................................................... 9.5 524 524 525 526 529 536 537 537 537 Creating an NFS Server ......................................................................................... 540 Initializing an NFS File System for Export ........................................... 540 Exporting a File System through NFS ................................................... 540 10 Flash File System Support: TrueFFS ................................................. 543 10.1 Introduction ............................................................................................................. 543 10.2 Overview of Implementation Steps .................................................................... 545 10.3 Creating a System with TrueFFS ......................................................................... 546 10.3.1 Selecting an MTD ..................................................................................... 546 10.3.2 Identifying the Socket Driver ................................................................. 547 10.3.3 Configuring VxWorks with TrueFFS .................................................... 548 Including File System Components ....................................................... 548 xx Contents Including the XBD Wrapper Component ............................................. Including the Core TrueFFS Component ............................................. Including Utility Components ............................................................... Including the MTD Component ............................................................. Including the Translation Layer Component ....................................... Adding the Socket Driver ....................................................................... 549 549 549 550 550 551 10.3.4 Building the System ................................................................................ 551 10.3.5 Formatting the Flash ................................................................................ 552 Specifying the Drive Number ................................................................. 552 Specifying Format Options ..................................................................... 552 10.3.6 Reserving a Region in Flash for a Boot Image ..................................... 554 Reserving a Fallow Region ..................................................................... 554 Writing the Boot Image to Flash ............................................................ 556 11 10.3.7 Mounting the Drive ................................................................................. 556 10.3.8 Testing the Drive ...................................................................................... 557 10.4 Using TrueFFS Shell Commands ........................................................................ 558 10.5 Using TrueFFS With HRFS .................................................................................. 560 10.5.1 TrueFFS With HRFS Code Example ...................................................... 560 10.5.2 TrueFFS With HRFS Shell Command Example ................................... 560 Error Detection and Reporting ............................................................ 563 11.1 Introduction ............................................................................................................. 563 11.2 Configuring Error Detection and Reporting Facilities ................................... 564 11.2.1 Configuring VxWorks ............................................................................. 565 11.2.2 Configuring the Persistent Memory Region ........................................ 565 11.2.3 Configuring Responses to Fatal Errors ................................................. 566 11.3 Error Records ........................................................................................................... 566 11.4 Displaying and Clearing Error Records ............................................................. 568 xxi VxWorks Kernel Programmer's Guide, 6.6 11.5 Fatal Error Handling Options .............................................................................. 569 11.5.1 Configuring VxWorks with Error Handling Options ......................... 570 11.5.2 Setting the System Debug Flag ............................................................... 571 Setting the Debug Flag Statically ........................................................... 571 Setting the Debug Flag Interactively ..................................................... 572 Setting the Debug Flag Programmatically ............................................ 572 12 11.6 Using Error Reporting APIs in Application Code ........................................... 572 11.7 Sample Error Record .............................................................................................. 573 Target Tools .......................................................................................... 575 12.1 Introduction ............................................................................................................. 576 12.2 Kernel Shell ............................................................................................................. 577 12.2.1 C Interpreter and Command Interpreter .............................................. 577 Switching Between Interpreters ............................................................ 578 Interpreter Commands and References ............................................... 578 12.2.2 Kernel and Host Shell Differences ......................................................... 578 12.2.3 Configuring VxWorks With the Kernel Shell ....................................... 581 Required Components ............................................................................. 581 Optional Components ............................................................................. 582 12.2.4 Configuring the Kernel Shell .................................................................. 584 12.2.5 Starting the Kernel Shell .......................................................................... 585 12.2.6 Using Kernel Shell Help .......................................................................... 585 12.2.7 Using Kernel Shell Control Characters ................................................. 586 12.2.8 Kernel Shell History ................................................................................. 586 12.2.9 Defining Kernel Shell Command Aliases ............................................. 587 12.2.10 Loading and Unloading Kernel Object Modules ................................. 587 12.2.11 Debugging with the Kernel Shell ........................................................... 588 Debugging SMP Systems with the Kernel Shell .................................. 588 12.2.12 Aborting Routines Executing from the Kernel Shell ........................... 589 xxii Contents 12.2.13 Console Login Security ............................................................................ 590 12.2.14 Using a Remote Login to the Kernel Shell ............................................ 591 Remote Login With telnet and rlogin .................................................... 591 Remote Login Security ............................................................................ 592 12.2.15 Launching a Shell Script Programmatically ......................................... 593 12.2.16 Executing Shell Commands Programmatically ................................... 593 12.2.17 Accessing Kernel Shell Data Programmatically .................................. 593 12.2.18 Using Kernel Shell Configuration Variables ........................................ 594 12.2.19 Adding Custom Commands to the Command Interpreter ............... 594 Creating A New Command .................................................................... 595 Sample Custom Commands ................................................................... 599 12.2.20 Creating a Custom Interpreter ............................................................... 599 Sample Custom Interpreter .................................................................... 602 12.3 Kernel Object-Module Loader ............................................................................. 603 12.3.1 Configuring VxWorks with the Kernel Object-Module Loader ........ 604 12.3.2 Kernel Object-Module Loader API ........................................................ 605 12.3.3 Summary List of Kernel Object-Module Loader Options .................. 606 12.3.4 Loading C++ Modules into the Kernel ................................................. 610 12.3.5 Specifying Memory Locations for Loading Objects ............................ 610 12.3.6 Guidelines and Caveats for Kernel Object-Module Loader Use ....... 611 Relocatable Object Files ........................................................................... Linking and Reference Resolution ......................................................... Load Sequence Requirements and Caveats .......................................... Resolving Common Symbols ................................................................. Resolving Weak Symbols ........................................................................ Stripping Symbols From Modules ......................................................... Function Calls, Relative Branches, and Load Failures ........................ Kernel Object Modules With SDA ......................................................... 12.4 611 612 613 614 615 615 616 616 Kernel Symbol Tables ........................................................................................... 617 Symbol Entries .......................................................................................... 617 Symbol Updates ....................................................................................... 618 Searching the Symbol Library ................................................................ 618 xxiii VxWorks Kernel Programmer's Guide, 6.6 12.4.1 Configuring VxWorks with Symbol Tables ......................................... 618 Configuration for User Symbol Tables ................................................. 618 Configuration for a System Symbol Table ............................................ 619 12.4.2 Creating a Built-In System Symbol Table ............................................. 620 Generating the Symbol Information ...................................................... 620 Compiling and Linking the Symbol File ............................................... 620 12.4.3 Creating a Loadable System Symbol Table .......................................... 621 Creating the .sym File .............................................................................. 621 Loading the .sym File ............................................................................... 621 12.4.4 Using the VxWorks System Symbol Table ........................................... 622 12.4.5 Synchronizing Host and Kernel Modules List and Symbol Table .... 623 12.4.6 Creating and Using User Symbol Tables .............................................. 623 12.5 Show Routines ........................................................................................................ 624 12.6 WDB Target Agent ................................................................................................. 626 12.6.1 Configuring VxWorks with the WDB Target Agent .......................... 627 Basic WDB Configuration ....................................................................... Host-Target Communication Options .................................................. Debugging Mode Options ...................................................................... Process Management Options ................................................................ Initialization Options ............................................................................... Additional Options .................................................................................. 628 628 632 633 634 634 12.6.2 WDB Target Agent and VxWorks SMP ................................................ 637 12.6.3 Using the WDB Target Agent with a TIPC Network .......................... 638 Target System Configuration ................................................................. 638 Establishing a Host-Target Connection ................................................ 639 12.6.4 Scaling the WDB Target Agent ............................................................... 639 12.6.5 WDB Target Agent and Exceptions ....................................................... 640 12.6.6 Starting the WDB Target Agent Before the VxWorks Kernel ............ 640 12.6.7 Creating a Custom WDB Communication Component ..................... 642 xxiv Contents 12.7 Common Problems ................................................................................................. 643 Kernel Shell Debugging Never Hits a Breakpoint .............................. Insufficient Memory ................................................................................ "Relocation Does Not Fit" Error Message ............................................. Missing Symbols ....................................................................................... Kernel Object-Module Loader is Using Too Much Memory ............. Symbol Table Unavailable ...................................................................... 13 643 643 644 645 645 646 C++ Development ................................................................................. 647 13.1 Introduction ............................................................................................................. 647 13.2 Configuring VxWorks for C++ ............................................................................ 648 13.3 C++ Code Requirements ....................................................................................... 649 13.4 Using C++ in Signal Handlers and ISRs .......................................................... 649 13.5 Downloadable Kernel Modules in C++ ............................................................ 650 13.6 13.5.1 Use a Single C++ Module ....................................................................... 650 13.5.2 Munching a C++ Application Module .................................................. 650 13.5.3 Calling Static Constructors and Destructors Interactively ................. 652 C++ Compiler Differences ................................................................................... 653 13.6.1 Template Instantiation ............................................................................. 654 13.6.2 Run-Time Type Information ................................................................... 656 13.7 Namespaces ............................................................................................................. 656 13.8 C++ Demo Example ............................................................................................... 657 xxv VxWorks Kernel Programmer's Guide, 6.6 PART II: MULTIPROCESSING TECHNOLOGIES 14 15 Overview of Multiprocessing Technologies ...................................... 661 14.1 Introduction ............................................................................................................. 661 14.2 VxWorks SMP ......................................................................................................... 662 14.3 Shared Memory Objects ........................................................................................ 662 14.4 Distributed Shared Memory ................................................................................ 662 14.5 TIPC Over Distributed Shared Memory ............................................................ 662 14.6 Message Channels .................................................................................................. 663 VxWorks SMP ....................................................................................... 665 15.1 Introduction ............................................................................................................ 666 15.2 Technology Overview .......................................................................................... 666 15.2.1 Terminology ............................................................................................. 667 15.2.2 VxWorks SMP Operating System Features ......................................... 668 15.2.3 VxWorks SMP Hardware ....................................................................... 669 15.2.4 Comparison of VxWorks SMP and AMP ............................................ 671 15.3 VxWorks SMP Configuration and Build .......................................................... 674 15.4 Booting VxWorks SMP ......................................................................................... 676 15.5 Programming for VxWorks SMP ....................................................................... 676 15.6 Spinlocks for Mutual Exclusion and Synchronization .................................. 679 15.6.1 ISR-Callable Spinlocks ............................................................................ 682 15.6.2 Task-Only Spinlocks ............................................................................... 682 15.6.3 Caveats With Regard to Spinlock Use .................................................. 683 15.6.4 Routines Restricted by Spinlock Use ..................................................... 683 xxvi Contents 15.7 15.8 CPU-Specific Mutual Exclusion ......................................................................... 685 15.7.1 CPU-Specific Mutual Exclusion for Interrupts ................................... 685 15.7.2 CPU-Specific Mutual Exclusion for Tasks ........................................... 686 Memory Barriers ..................................................................................................... 687 Read Memory Barrier .............................................................................. 688 Write Memory Barrier ............................................................................. 689 Read/Write Memory Barrier .................................................................. 689 15.9 Atomic Memory Operations ................................................................................. 690 15.10 CPU Affinity ........................................................................................................... 691 15.10.1 Task CPU Affinity ................................................................................... 691 15.10.2 Interrupt CPU Affinity ........................................................................... 694 15.11 CPU Information and Management .................................................................. 694 CPU Information and Management Routines ..................................... 694 CPU Set Variables and Macros ............................................................... 696 15.12 Debugging SMP Code .......................................................................................... 698 15.13 Optimizing SMP Performance ............................................................................ 699 15.14 Sample Programs ................................................................................................... 702 15.15 Migrating Code to VxWorks SMP ..................................................................... 702 15.15.1 Code Migration Path ................................................................................ 703 15.15.2 Overview of Migration Issues ............................................................... 705 15.15.3 RTP Applications and SMP .................................................................... 706 15.15.4 Implicit Synchronization of Tasks ......................................................... 706 15.15.5 Synchronization and Mutual Exclusion Facilities ............................... 707 15.15.6 VxWorks SMP Variants of Uniprocessor Routines ............................. 708 cacheLib Restrictions ............................................................................... 708 vmBaseLib Restrictions ........................................................................... 709 xxvii VxWorks Kernel Programmer's Guide, 6.6 15.15.7 Unsupported Uniprocessor Routines and SMP Alternatives ........... 709 Interrupt Locking: intLock( ) and intUnlock( ) .................................... Task Locking: taskLock( ) and taskUnlock( ) ....................................... Task Locking in RTPs: taskRtpLock( ) and taskRtpUnlock( ) ............ Task Variable Management: taskVarLib .............................................. Task Local Storage: tlsLib ........................................................................ 710 711 711 712 712 15.15.8 SMP CPU-Specific Variables and Uniprocessor Global Variables .... 712 SMP Per-CPU Variables .......................................................................... 713 Uniprocessor-Only Global Variables ..................................................... 714 15.15.9 Memory-Access Attributes ..................................................................... 714 15.15.10 Drivers and BSPs ...................................................................................... 715 16 Shared-Memory Objects: VxMP .......................................................... 717 16.1 Introduction ............................................................................................................. 717 16.2 Using Shared-Memory Objects ........................................................................... 718 16.2.1 Multiprocessor-Uniprocessor Portability ............................................. 719 16.2.2 Multiprocessing and Byte Ordering ...................................................... 719 16.2.3 Restrictions on Shared Memory Object Use ......................................... 720 16.2.4 Publishing Objects With the Name Database ...................................... 720 16.2.5 Shared Semaphores .................................................................................. 722 16.2.6 Shared Message Queues .......................................................................... 728 16.2.7 Shared-Memory Allocator ...................................................................... 733 Shared-Memory System Partition .......................................................... User-Created Partitions ........................................................................... Using the Shared-Memory System Partition ........................................ Using User-Created Partitions ............................................................... Side Effects of Shared-Memory Partition Options .............................. 733 734 735 738 741 16.3 System Requirements ............................................................................................ 741 16.4 Performance Considerations ................................................................................ 742 xxviii Contents 16.5 17 Configuring VxWorks for Shared Memory Objects ...................................... 744 16.5.1 Maximum Number of CPUs ................................................................... 744 16.5.2 Cache Coherency ...................................................................................... 744 16.5.3 Mailbox Interrupts and Bus Interrupts ................................................. 745 16.5.4 Shared-Memory Anchor ......................................................................... 745 16.5.5 Shared-Memory Region .......................................................................... 746 16.5.6 Numbers of Shared Memory Objects .................................................... 747 16.5.7 Dual-Port or External Memory .............................................................. 748 16.5.8 Configuration Example ........................................................................... 750 16.6 Displaying Information About Shared Memory Objects .............................. 752 16.7 Troubleshooting ..................................................................................................... 752 16.7.1 Configuration Problems .......................................................................... 753 16.7.2 Troubleshooting Techniques .................................................................. 754 Distributed Shared Memory: DSHM ................................................... 755 17.1 Introduction ............................................................................................................ 755 17.2 Technology Overview .......................................................................................... 756 17.2.1 Architecture .............................................................................................. 757 DSHM Management Service and Custom Services ............................ 758 Hardware Interface .................................................................................. 758 17.2.2 Communication Model .......................................................................... 759 Broadcasting .............................................................................................. 759 Send Operation ......................................................................................... 762 Broadcast Operation ................................................................................ 763 17.3 Configuring VxWorks for DSHM ...................................................................... 763 17.3.1 Components and Parameters ................................................................. 764 xxix VxWorks Kernel Programmer's Guide, 6.6 17.4 17.5 Developing Custom Services .............................................................................. 767 17.4.1 Service Numbers ..................................................................................... 768 17.4.2 DSHM Messaging Protocols and Macro Functions ........................... 769 17.4.3 DSHM Service APIs ................................................................................ 770 17.4.4 Service Code Example ............................................................................ 771 Developing a Hardware Interface ...................................................................... 777 17.5.1 Driver Initialization ................................................................................. 778 17.5.2 Callbacks .................................................................................................... 778 17.5.3 Registering with the DSHM MUX ......................................................... 782 17.5.4 Messaging Support ................................................................................. 782 Shared Memory Messaging Support ..................................................... 783 Shared Memory Lock-Less Discovery ................................................... 785 18 17.5.5 Management Service ............................................................................... 785 17.5.6 DSHM Hardware Interface APIs .......................................................... 786 Message Channels ............................................................................... 787 18.1 Introduction ............................................................................................................. 787 18.2 Message Channel Facilities .................................................................................. 789 18.3 Multi-Node Communication with TIPC ............................................................ 791 18.4 Single-Node Communication with COMP and DSI ....................................... 791 Express Messaging ................................................................................... 792 Show Routines .......................................................................................... 792 18.4.1 18.5 COMP Socket Support with DSI ............................................................ 793 Socket Name Service .............................................................................................. 795 18.5.1 Multi-Node Socket Name Service .......................................................... 796 18.5.2 snsShow( ) Example ................................................................................. 797 xxx Contents 18.6 18.7 Socket Application Libraries ............................................................................... 799 18.6.1 SAL Server Library .................................................................................. 800 18.6.2 SAL Client Library ................................................................................... 802 Configuring VxWorks for Message Channels .................................................. 803 COMP, DSI, and SAL Components ....................................................... 803 SNS Component Options ........................................................................ 803 Show Routines .......................................................................................... 805 18.8 Comparison of Message Channels and Message Queues .............................. 806 Index .............................................................................................................. 809 xxxi VxWorks Kernel Programmer's Guide, 6.6 xxxii PART I Core Technologies 1 Overview ............................................................. 3 2 Kernel .................................................................. 7 3 Boot Loader ........................................................ 131 4 Multitasking ........................................................ 157 5 POSIX Facilities .................................................. 251 6 Memory Management ......................................... 315 7 I/O System ........................................................... 359 8 Local File Systems ............................................. 451 9 Network File System: NFS ................................. 523 10 Flash File System Support: TrueFFS ................ 543 11 Error Detection and Reporting .......................... 563 12 Target Tools ........................................................ 575 13 C++ Development ............................................... 647 1 VxWorks Kernel Programmer's Guide, 6.6 2 1 Overview 1.1 Introduction 3 1.2 Related Documentation Resources 4 1.3 VxWorks Configuration and Build 5 1.1 Introduction This guide describes the VxWorks operating system, and how to use VxWorks facilities in the development of real-time systems and applications. The first part, Core Technologies, covers the following topics: ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ kernel facilities, kernel-based applications, and kernel customization boot loader multitasking facilities POSIX facilities memory management I/O system local file systems Network File System (NFS) flash file system support with TrueFFS error detection and reporting target tools, such as the kernel shell, kernel object-module loader, and target symbol table C++ development 3 VxWorks Kernel Programmer's Guide, 6.6 The second part of this guide describes VxWorks multiprocessor technologies. For an introduction to this material, see 14. Overview of Multiprocessing Technologies. NOTE: This book provides information about facilities available in the VxWorks kernel. For information about facilities available to real-time processes, see the VxWorks Application Programmer’s Guide. 1.2 Related Documentation Resources The companion volume to this book, the VxWorks Application Programmer’s Guide, provides material specific process-based (RTP) applications and process management. Detailed information about VxWorks libraries and routines is provided in the VxWorks API references. Information specific to target architectures is provided in the VxWorks BSP references and in the VxWorks Architecture Supplement. For information about BSP and driver development, see the VxWorks BSP Developer’s Guide and the VxWorks Device Driver Guide. The VxWorks networking facilities are documented in the Wind River Network Stack for VxWorks 6 Programmer’s Guide and the VxWorks PPP Programmer’s Guide. For information about migrating applications, BSPs, drivers, and projects from previous versions of VxWorks and the host development environment, see the VxWorks Migration Guide and the Wind River Workbench Migration Guide. The Wind River IDE and command-line tools are documented in the Wind River Workbench User’s Guide, the VxWorks Command-Line Tools User’s Guide, the Wind River compiler and GNU compiler guides, and the Wind River tools API and command-line references. 4 1 Overview 1.3 VxWorks Configuration and Build 1.3 VxWorks Configuration and Build 1 This document describes VxWorks features; it does not go into detail about the mechanisms by which VxWorks-based systems and applications are configured and built. The tools and procedures used for configuration and build are described in the Wind River Workbench User’s Guide and the VxWorks Command-Line Tools User’s Guide. NOTE: In this guide, as well as in the VxWorks API references, VxWorks components and their configuration parameters are identified by the names used in component description files. The names take the form, for example, of INCLUDE_FOO and NUM_FOO_FILES (for components and parameters, respectively). You can use these names directly to configure VxWorks using the command-line configuration facilities. Wind River Workbench displays descriptions of components and parameters, as well as their names, in the Components tab of the Kernel Configuration Editor. You can use the Find dialog to locate a component or parameter using its name or description. To access the Find dialog from the Components tab, type CTRL+F, or right-click and select Find. 5 VxWorks Kernel Programmer's Guide, 6.6 6 2 Kernel 2.1 Introduction 7 2.2 Kernel Architecture 9 2.3 System Startup 13 2.4 VxWorks Configuration 14 2.5 Power Management 40 2.6 Kernel Applications 51 2.7 Custom Kernel Libraries 67 2.8 Custom VxWorks Components and CDFs 67 2.9 Custom System Calls 100 2.10 Custom Scheduler 118 2.1 Introduction This chapter provides an overview of the VxWorks kernel architecture and detailed discussions of those features of interest to developers who work directly with kernel facilities. In general, kernel developers can modify and extend the VxWorks kernel in following ways: 7 VxWorks Kernel Programmer's Guide, 6.6 ■ By reconfiguring and rebuilding VxWorks with various standard components to suit the needs of their application development environment, as well as the needs of their deployed products. ■ By creating kernel applications that can either be interactively downloaded and run on a VxWorks target system, or configured to execute at boot time and linked with the operating system image. ■ By creating custom kernel libraries that can be built into the operating system. ■ By creating custom VxWorks components—such as file systems or networking protocols—that can be configured into VxWorks using the operating system configuration utilities. ■ By extending the kernel system-call interface with custom APIs that should be accessible to applications running in user space (as real-time process—RTP— applications). ■ By creating a custom scheduler for use in place of the traditional VxWorks scheduler or the POSIX thread scheduler. See 2.4 VxWorks Configuration, p.14; as well as other chapters throughout this book for information about VxWorks facilities and their use. Chapter 4. Multitasking, for example, includes discussion of features that are available only in the kernel (such as ISRs and watchdog timers). Section 2.6 Kernel Applications, p.51 provides information about creating kernel applications. For information about RTP applications, see the VxWorks Application Programmer’s Guide: Applications and Processes. Instructions for creating custom kernel libraries is provided in the VxWorks Command-Line Tools User’s Guide. Only brief mention of this topic is given in this book in 2.7 Custom Kernel Libraries, p.67. See 2.8 Custom VxWorks Components and CDFs, p.67, 2.9 Custom System Calls, p.100, and 2.10 Custom Scheduler, p.118 for information about extending the operating system. Developers can also write or port drivers and BSPs for VxWorks. These topics are covered by other books in the VxWorks documentation set; see the VxWorks Device Driver’s Guide and the VxWorks BSP Developer’s Guide. 8 2 Kernel 2.2 Kernel Architecture 2.2 Kernel Architecture Historically, the VxWorks operating system provided a single memory space with no segregation of the operating system from user applications. All tasks ran in supervisor mode. Although this model afforded performance and flexibility when developing applications, only skilled programming could ensure that kernel facilities and applications coexisted in the same memory space without interfering with one another.1 With the release of VxWorks 6.0, the operating system provides support for real-time processes (RTPs) that includes execution of applications in user mode and other features common to operating systems with a clear delineation between kernel and applications. This architecture is often referred to as the process model. VxWorks has adopted this model with a design specifically aimed to meet the requirements of determinism and speed that are required for hard real-time systems. (For information about VxWorks processes and developing applications to run in processes, see VxWorks Application Programmer’s Guide: Applications and Processes.) VxWorks 6.x provides full MMU-based protection of both kernel and user space. At the same time, VxWorks 6.x maintains a high level of backward compatibility with VxWorks 5.5. Applications developed for earlier versions of VxWorks, and designed to run in kernel space, can be migrated to VxWorks 6.x kernel space with minimal effort (in most cases, merely re-compilation). For more information on this topic, see the VxWorks Migration Guide. Naturally, new applications can be designed for kernel space as well, when other considerations outweigh the advantages of protection that executing applications as processes affords. These considerations might include: ■ Size. The overall size of a system is smaller without components that provided for processes and MMU support. ■ Speed. Depending on the number of system calls an application might make, or how much I/O it is doing when running as a process in user space, it might be faster running in the kernel. 1. The VxWorks 5.x optional product VxVMI provides write protection of text segments and the VxWorks exception vector table, as well as an architecture-independent interface to the CPU’s memory management unit (MMU). In addition, specialized variants of VxWorks such as VxWorks AE and VxWorks AE653 provide memory protection, but in a manner different from that provided in the current release. 9 2 VxWorks Kernel Programmer's Guide, 6.6 ■ Kernel-only features. Features such as watchdog timers, ISRs, and VxMP are available only in the kernel. In some cases, however, there are alternatives for process-based applications (POSIX timers, for example). ■ Hardware access. If the application requires direct access to hardware, it can only do so from within the kernel. VxWorks is flexible in terms of both the modularity of its features and its extensibility. The operating system can be configured as a minimal kernel that provides a task scheduler, interrupt handling, dynamic memory management, and little else. Or, it can be configured with components for executing applications as processes, file systems, networking, error detection and reporting, and so on. The operating system can also be extended by adding custom components or modules to the kernel itself (for example, for new file systems, networking protocols, or drivers). The system call interface can then be extended by adding custom APIs, which makes them available to process-based applications. 2.2.1 Operating System Facilities VxWorks provides a core set of facilities that are commonly provided by the kernel of a multitasking operating system: ■ Startup facilities for system initialization (see 2.3 System Startup, p.13). ■ Clocks and timers (see 4.19 Watchdog Timers, p.239 and 5.7 POSIX Asynchronous I/O, p.263). ■ Exception and interrupt handling (see Exception Task, p.12, 4.6 Task Exception Handling, p.187, 4.18 Signals, p.226, and 4.20 Interrupt Service Routines, p.241). ■ Task management (see 4.2 Tasks and Multitasking, p.160). ■ Process management (see the VxWorks Application Programmer’s Guide: Applications and Processes). ■ A system call interface for applications executing in processes (see VxWorks Application Programmer’s Guide: Applications and Processes and 2.9 Custom System Calls, p.100). ■ Intertask and interprocess communication (see 4.8 Intertask and Interprocess Communication, p.193. ■ Signals (see 4.18 Signals, p.226). ■ Resource reclamation (see VxWorks Application Programmer’s Guide: Applications and Processes). 10 2 Kernel 2.2 Kernel Architecture ■ Memory management (see 6. Memory Management). ■ I/O system (see 7. I/O System). ■ File systems (see 8. Local File Systems). ■ NFS (see 9. Network File System: NFS). 2 In addition, the VxWorks kernel also provides: ■ The WDB target agent, which is required for using the host development tools with VxWorks. It carries out requests transmitted from the tools (by way of the target server) and replies with the results (see 12.6 WDB Target Agent, p.626). ■ Facilities for error detection and reporting (see 11. Error Detection and Reporting). ■ A target-based shell for direct user interaction, with a command interpreter and a C-language interpreter (see 12.2 Kernel Shell, p.577). ■ A specialized facilities for multi-processor intertask communication through shared memory (see 16. Shared-Memory Objects: VxMP). For information about basic networking facilities, see the Wind River Network Stack for VxWorks 6 Programmer’s Guide. 2.2.2 System Tasks Depending on its configuration, VxWorks includes a variety of system tasks, which are always running. These are described below. Root Task The root task tRootTask is the first task executed by the kernel. The entry point of the root task is usrRoot( )initializes most VxWorks facilities. It spawns such tasks as the logging task, the exception task, the network task, and the tRlogind daemon. Normally, the root task terminates and is deleted after all initialization has completed. For more information tRootTask and usrRoot( ), see the VxWorks BSP Developer’s Guide. Logging Task The log task, tLogTask, is used by VxWorks modules to log system messages without having to perform I/O in the current task context. For more information, see 7.7 Asynchronous Input/Output, p.381 and the API reference entry for logLib. 11 VxWorks Kernel Programmer's Guide, 6.6 Exception Task The exception task, tExcTask, supports the VxWorks exception handling package by performing functions that cannot occur at interrupt level. It is also used for actions that cannot be performed in the current task’s context, such as task suicide. It must have the highest priority in the system. Do not suspend, delete, or change the priority of this task. For more information, see the reference entry for excLib. Network Task The tNet0 task is the default network daemon. It handles the task-level (as opposed to interrupt-level) processing required by the VxWorks network. For systems that have been configured with more than one network daemon, the task names are tNetn. The task is primarily used by network drivers. Configure VxWorks with the INCLUDE_NET_DAEMON component to spawn the tNet0 task. For more information on tNet0, see the Wind River Network Stack for VxWorks 6 Programmer’s Guide. WDB Target Agent Task The WDB target agent task, tWdbTask, is created if the target agent is set to run in task mode. It services requests from the host tools (by way of the target server); for information about this server, see the host development environment documentation. Configure VxWorks with the INCLUDE_WDB component to include the target agent. See 12.6 WDB Target Agent, p.626 for more information about WDB. Tasks for Optional Components The following VxWorks system tasks are created if their components are included in the operating system configuration. tShellnum If you have included the kernel shell in the VxWorks configuration, it is spawned as a task. Any routine or task that is invoked from the kernel shell, rather than spawned, runs in the tShellnum context. The task name for a shell on the console is tShell0. The kernel shell is re-entrant, and more than one shell task can run at a time (hence the number suffix). In addition, if a user logs in remotely (using rlogin or telnet) to a VxWorks target, the name reflects that fact as well. For example, tShellRem1. For more information, see 12.2 Kernel Shell, p.577. Configure VxWorks with the INCLUDE_SHELL component to include the kernel shell. 12 2 Kernel 2.3 System Startup tRlogind If you have included the kernel shell and the rlogin facility in the VxWorks configuration, this daemon allows remote users to log in to VxWorks. It accepts a remote login request from another VxWorks or host system and spawns tRlogInTask_hexNumber and tRlogOutTask_hexNumber (for example, tRlogInTask_5c4d0). These tasks exist as long as the remote user is logged on. Configure VxWorks with the INCLUDE_RLOGIN component to include the rlogin facility. tTelnetd If you have included the kernel shell and the telnet facility in the VxWorks configuration, this daemon allows remote users to log in to VxWorks with telnet. It accepts a remote login request from another VxWorks or host system and spawns the input task tTelnetInTask_hexNumber and output task tTelnetOutTask_hexNumber. These tasks exist as long as the remote user is logged on. Configure VxWorks with the INCLUDE_TELNET component to include the telnet facility. tPortmapd If you have included the RPC facility in the VxWorks configuration, this daemon is RPC server that acts as a central registrar for RPC services running on the same machine. RPC clients query the tPortmapd daemon to find out how to contact the various servers. Configure VxWorks with the INCLUDE_RPC component to include the portmap facility. tJobTask The tJobTask executes jobs—that is, function calls—on the behalf of tasks. (The tExcTask task executes jobs on the behalf of ISRs.) It runs at priority 0 while waiting for a request, and dynamically adjusts its priority to match that of the task that requests job execution. Configure VxWorks with the INCLUDE_JOB_TASK component to include the job facility. For more information see, 4.4.6 Task Deletion and Deletion Safety, p.180. 2.3 System Startup When a VxWorks system is powered on, the boot loader copies an operating system image into memory and directs the CPU to begin executing it. The boot loader is most often located in ROM (although it can also be stored on a disk). The VxWorks image can be stored on a host or network file system, as is usually the 13 2 VxWorks Kernel Programmer's Guide, 6.6 case during development—or stored in ROM with the boot loader, as is often the case with production units. The VxWorks boot loader is actually a scaled-down version of VxWorks itself, whose sole purpose is to load a system image and initiate its execution. (See 3. Boot Loader.) For more information about system startup, see the VxWorks BSP Developer's Guide: Overview of a BSP. 2.4 VxWorks Configuration VxWorks is a flexible, scalable operating system with numerous facilities that can included, excluded, variously configured, and extended with customized technologies, depending on the requirements of your applications and system, and the stage of the development cycle. VxWorks distributions include default system images for each supported BSP. Each system image is a binary module that can be booted and run on a target system. A system image consists of a set of components linked together into a single non-relocatable object module with no unresolved external references. The default system images are designed for the development environment. They contain the basic set of components that are necessary to interact with the system using host development tools. In most cases, you will find the supplied system image adequate for initial development (provided the default drivers are appropriate). Using a default VxWorks image, you can interactively download and run kernel applications. During the development cycle you may want to reconfigure and rebuild VxWorks with components specifically selected to support your applications and development requirements. If, for example, you configure VxWorks with the appropriate components and initialization settings, you can link kernel applications with VxWorks and start them automatically at boot time (see 2.6 Kernel Applications, p.51). You can also configure VxWorks with support for process-based applications, to store them as part of the system image in ROMFS, and to run them interactively and automatically (see VxWorks Application Programmer’s Guide: Applications and Processes). If the VxWorks components provided by Wind River do not provide all the facilities required for your system, you can create custom facilities, such as new file systems and networking protocols, and package them as components (see 2.8 Custom VxWorks Components and CDFs, p.67), add new system calls for 14 2 Kernel 2.4 VxWorks Configuration process-based applications (see 2.9 Custom System Calls, p.100), create your own scheduler (see 2.10 Custom Scheduler, p.118), and so on. Finally, for production systems, you will want to reconfigure VxWorks with only those components needed for deployed operation, and to build it as the appropriate type of system image (see 2.4.1 VxWorks Image Types, p.15). For production systems you will likely want to remove components required for host development support, such as the WDB target agent and debugging components (INCLUDE_WDB and INCLUDE_DEBUG), as well as to remove any other operating system components not required to support your application. Other considerations include reducing the memory requirements of the system, speeding up boot time, and security issues. For information about using the Workbench and command-line tools to configure and build VxWorks, see the Wind River Workbench User’s Guide and the VxWorks Command-Line Tools User’s Guide. 2.4.1 VxWorks Image Types Different types of VxWorks system images can be produced for a variety of storage, loading, and execution scenarios. Default versions of the following images are provided in the VxWorks installation. Customized versions with different components can also be created. Note that only one image type requires a boot loader, and that the others are self-booting. The various VxWorks image types, their use, and behavior are: vxWorks This VxWorks image type is intended for use during development and is often referred to as downloadable. It is also useful for production systems in which the boot loader and system image are stored on disk. In a development environment, the image is usually stored on the host system (or a server on the network), downloaded to the target system by the boot loader, and loaded into RAM. The symbol table is maintained on the host (in the file vxWorks.sym), where it is used by the host development tools. Leaving the symbol table on the host keeps the image size down and reduces boot time. If VxWorks is reconfigured with the INCLUDE_STANDALONE_SYM_TBL component, the symbol table is included in the VxWorks image. vxWorks_rom A VxWorks image that is stored in ROM on the target. It copies itself to RAM and then makes the processor switch execution to RAM. Because the image is not compressed, it is larger than the other ROM-based images and therefore 15 2 VxWorks Kernel Programmer's Guide, 6.6 has a slower startup time; but it has a faster execution time than vxWorks_romResident. vxWorks_romCompress A VxWorks image that is stored in ROM on the target. It is almost entirely compressed, but has small uncompressed portion executed by the processor immediately after power up/reboot. This small portion is responsible for decompressing the compressed section of the ROM image into RAM and for making the processor switch execution to RAM. The compression of the image allows it to be much smaller than other images. However the decompression operation increases the boot time. It takes longer to boot than vxWorks_rom but takes up less space than other ROM-based images. The run-time execution is the same speed as vxWorks_rom. vxWorks_romResident A VxWorks image that is stored in ROM on the target. It copies only the data segment to RAM on startup; the text segment stays in ROM. Thus it is described as being ROM-resident. It has the fastest startup time and uses the smallest amount of RAM, but it runs slower than the other image types because the ROM access required for fetching instructions is slower than fetching them from RAM. It is obviously useful for systems with constrained memory resources. The default VxWorks image files can be found in sub-directories under installDir/vxworks-6.x/target/proj/projName. For example: /home/moi/myInstallDir/vxworks-6.x/target/proj/wrSbc8260_diab/default_rom/vxWorks_rom For many production systems it is often necessary to store a kernel application module that is linked with VxWorks in ROM. VxWorks can be configured to execute the application automatically at boot time. The system image can also simply store the application module to allow for its being called by other programs, or for interactive use by end-users (for example, diagnostic programs). To produce a ROM-based system, you must link the module with VxWorks, and build an image type that is suitable for ROM. See 2.6.8 Linking Kernel Application Object Modules with VxWorks, p.64. If you wish to have the application start automatically at boot time, you must also configure VxWorks to do so (see 2.6.10 Configuring VxWorks to Run Applications Automatically, p.66). Also see 2.6.9 Image Size Considerations, p.65. Note that, during development, VxWorks must be configured with the WDB target agent communication interface that is required for the type of connection used between your host and target system (network, serial, and so on). By default, it is configured for an Enhanced Network Driver (END) connection. For more 16 2 Kernel 2.4 VxWorks Configuration information, see 12.6 WDB Target Agent, p.626. Also note that before you use the host development tools such as the shell and debugger, you must start a target server that is configured for the same mode of communication. For information about configuring VxWorks with different operating system facilities (components), see 2.4.3 Device Driver Selection, p.22. If you are going to store boot image in flash, and want to user TrueFFS as well, see 10.3.6 Reserving a Region in Flash for a Boot Image, p.554. 2.4.2 VxWorks Components A VxWorks component is the basic unit of functionality with which VxWorks can be configured. While some components are autonomous, others may have dependencies on other components, which must be included in the configuration of the operating system for run-time operation. The kernel shell is an example of a component with many dependencies. The symbol table is an example of a component upon which other components depend (the kernel shell and module loader; for more information, see 12. Target Tools). The names, descriptions, and configurable features of VxWorks can be displayed with the GUI configuration facilities in Workbench. Workbench provides facilities for configuring VxWorks with selected components, setting component parameters, as well as automated mechanisms for determining dependencies between components during the configuration and build process. The command-line operating system configuration tool—vxprj—uses the naming convention that originated with configuration macros to identify individual operating system components. The convention identifies components with names that begin with INCLUDE. For example, INCLUDE_MSG_Q is the message queue component. In addition to configuration facilities, the vxprj tool provides associated features for listing the components included in a project, and so on. For information about the Workbench and command-line facilities used for configuring and building VxWorks, see the Wind River Workbench User’s Guide and the VxWorks Command-Line Tools User’s Guide. Textual configuration files identify components with macro names that begin with INCLUDE, as well as with user-friendly descriptions. (For information about configuration files, see 2.8.4 Component Description Language, p.79.) In this book, components are identified by their macro name. The GUI configuration facilities provide a search facility for finding individual components in the GUI component tree based on the macro name. 17 2 VxWorks Kernel Programmer's Guide, 6.6 Some of the commonly used VxWorks components are described in Table 2-1. Names that end in XXX represent families of components, in which the XXX is replaced by a suffix for individual component names. For example, INCLUDE_CPLUS_XXX refers to a family of components that includes INCLUDE_CPLUS_MIN and others. Note that Table 2-1 does not include all components provided in the default configuration of VxWorks, and that the VxWorks simulator provides more components by default. Table 2-1 Key VxWorks Components Component INCLUDE_ANSI_XXX Default * Description Various ANSI C library options Parse boot device configuration information INCLUDE_BOOTLINE_INIT INCLUDE_BOOTP * BOOTP support INCLUDE_CACHE_SUPPORT * Cache support INCLUDE_CPLUS * Bundled C++ support INCLUDE_CPLUS_XXX Various C++ support options INCLUDE_DEBUG Kernel shell debugging facilities INCLUDE_EDR_XXX Error detection and reporting facilities. INCLUDE_DOSFS DOS-compatible file system INCLUDE_FLOATING_POINT * Floating-point I/O INCLUDE_FORMATTED_IO * Formatted I/O FTP server support INCLUDE_FTP_SERVER INCLUDE_IO_SYSTEM 18 * I/O system and associated interfaces. Directory and path manipulation APIs (for more information, see 7.2 Configuring VxWorks With I/O Facilities, p.362) 2 Kernel 2.4 VxWorks Configuration Table 2-1 Key VxWorks Components (cont’d) Component Default Description 2 Target-resident kernel object module loader package INCLUDE_LOADER INCLUDE_LOGGING * Logging facility INCLUDE_MEM_MGR_BASIC * Core partition memory manager INCLUDE_MEM_MGR_FULL * Full-featured memory manager INCLUDE_MIB2_XXX Various MIB-2 options INCLUDE_MMU_BASIC * Bundled MMU support INCLUDE_MSG_Q * Message queue support INCLUDE_NETWORK * Network subsystem code INCLUDE_NFS Network File System (NFS) INCLUDE_NFS_SERVER NFS server INCLUDE_PIPES * Pipe driver INCLUDE_POSIX_XXX Various POSIX options INCLUDE_PROTECT_TEXT Text segment write protection INCLUDE_PROTECT_VEC_TABLE Vector table write protection INCLUDE_PROXY_CLIENT * Proxy ARP client support INCLUDE_PROXY_SERVER Proxy ARP server support INCLUDE_RAWFS Raw file system INCLUDE_RLOGIN Remote login with rlogin INCLUDE_ROMFS ROMFS file system INCLUDE_RTP Real-time process support. INCLUDE_SCSI SCSI support INCLUDE_SCSI2 SCSI-2 extensions 19 VxWorks Kernel Programmer's Guide, 6.6 Table 2-1 Key VxWorks Components (cont’d) Component Default Description INCLUDE_SECURITY Remote login security package INCLUDE_SELECT Select facility INCLUDE_SEM_BINARY * Binary semaphore support INCLUDE_SEM_COUNTING * Counting semaphore support INCLUDE_SEM_MUTEX * Mutual exclusion semaphore support INCLUDE_SHELL Kernel (target) shell INCLUDE_XXX_SHOW Various system object show facilities INCLUDE_SIGNALS * Software signal facilities INCLUDE_SM_OBJ Shared memory object support (requires VxMP) INCLUDE_SNMPD SNMP agent INCLUDE_SPY Task activity monitor INCLUDE_STDIO * Standard buffered I/O package INCLUDE_SW_FP Software floating point emulation package INCLUDE_SYM_TBL Target-resident symbol table support INCLUDE_TASK_HOOKS * Kernel call-out support INCLUDE_TASK_VARS * Task variable support Remote login with telnet INCLUDE_TELNET INCLUDE_TFTP_CLIENT INCLUDE_TFTP_SERVER 20 * TFTP client support TFTP server support 2 Kernel 2.4 VxWorks Configuration Table 2-1 Key VxWorks Components (cont’d) Component INCLUDE_TIMEX Default * Description 2 Function execution timer INCLUDE_TRIGGERING Function execution timer INCLUDE_UNLOADER Target-resident kernel object module unloader package INCLUDE_VXEVENTS VxWorks events support. INCLUDE_WATCHDOGS * Watchdog support INCLUDE_WDB * WDB target agent (see 12.6 WDB Target Agent, p.626) INCLUDE_WDB_TSFS * Target server file system INCLUDE_WINDVIEW System Viewer command server (see the Wind River System Viewer User’s Guide) By default, VxWorks includes both libc and GNU libgcc, which are provided with the INCLUDE_ALL_INTRINSICS component. If you wish to exclude one or the other library, you can do so by reconfiguring the kernel with either INCLUDE_DIAB_INTRINSICS or INCLUDE_GNU_INTRINSICS, respectively. Note that these libraries are available in the kernel to enable dynamically downloading and running kernel object modules. 21 VxWorks Kernel Programmer's Guide, 6.6 2.4.3 Device Driver Selection Device drivers are provided as VxWorks components that can be added to or removed from a system using Workbench and vxprj. Some drivers are VxBus-compliant, and others (legacy drivers) are not. NOTE: Only VxBus-compatible drivers can be used with the symmetric multiprocessing (SMP) configuration of VxWorks. For general information about VxWorks SMP and about migration, see 15. VxWorks SMP and 15.15 Migrating Code to VxWorks SMP, p.702. Note that the component names for VxBus drivers do not have the leading INCLUDE_ element (for example, DRV_SIO_NS16550), whereas the names for non-VxBus drivers do (for example, INCLUDE_ELT_3C509_END). For information about the VxBus facility, see the VxWorks Device Driver Developer’s Guide. 2.4.4 VxWorks Configuration Profiles In addition to components and component bundles, configuration profiles can be used to configure a VxWorks system. Profiles provide a convenient way of providing a base line of operating system functionality that is different from the default configuration available with the VxWorks product installation. The following profiles are available: PROFILE_MINIMAL_KERNEL—Minimal VxWorks Kernel Profile Provides the lowest level of services at which a VxWorks system can operate. It consists of the micro-kernel, and basic CPU and BSP support. This profile is meant to provide a very small VxWorks system that can support multitasking and interrupt management at a very minimum, but semaphores and watchdogs are also supported by default. (See 2.4.5 Small VxWorks Configuration Profiles, p.24.) PROFILE_BASIC_KERNEL—Basic VxWorks Kernel Profile Builds on the minimal kernel profile, adding support for message queues, task hooks, memory allocation and de-allocation, and basic I/O facilities. Applications based on this profile can be more dynamic and feature rich than the minimal kernel. (See 2.4.5 Small VxWorks Configuration Profiles, p.24.) 22 2 Kernel 2.4 VxWorks Configuration PROFILE_BASIC_OS—Basic VxWorks OS Profile Provides a small operating system on which higher level constructs and facilities can be built. It supports a full I/O system, file descriptors, and related ANSI routines. It also supports task and environment variables, signals, pipes, coprocessor management, and a ROMFS file system. (See 2.4.5 Small VxWorks Configuration Profiles, p.24.) PROFILE_COMPATIBLE—VxWorks 5.5 Compatible Profile Provides the minimal configuration that is compatible with VxWorks 5.5. PROFILE_DEVELOPMENT—VxWorks Kernel Development Profile Provides a VxWorks kernel that includes development and debugging components. PROFILE_ENHANCED_NET—VxWorks Enhanced Network Profile Adds components appropriate for typical managed network client host devices to the default profile. The primary components added are the DHCP client and DNS resolver, the Telnet server (shell not included), and several command-line-style configuration utilities. PROFILE_CERT—VxWorks DO-178 Certification Profile Provides a DO-178B Level A-certifiable API subset of the VxWorks operating system. PROFILE_BOOTAPP—VxWorks Boot Loader Profile Provides a VxWorks boot loader. For more information, see 3.7 Customizing and Building Boot Loaders, p.146. 23 2 VxWorks Kernel Programmer's Guide, 6.6 2.4.5 Small VxWorks Configuration Profiles VxWorks can be scaled below the size of the default operating system using special configuration profiles (sometimes referred to as source-scalable or scalable profiles). They provide three levels of operating system functionality, starting with a minimal kernel through a basic operating system. These profiles do not support networking facilities. The small configuration profiles are as follows: ■ PROFILE_MINIMAL_KERNEL—The minimal kernel profile provides the lowest level of services at which a VxWorks system can operate. It consists of the microkernel, and basic CPU and BSP support. This profile creates a very small VxWorks systems that can support multitasking and interrupt management. It does not provide support for dynamic memory allocation; all objects must be statically instantiated. For more information see Minimal Kernel Profile, p.28. ■ PROFILE_BASIC_KERNEL—The basic kernel profile builds on the minimal kernel profile, adding support for message queues, task hooks, dynamic memory allocation and de-allocation, and a basic I/O system. For more information, see Basic Kernel Profile, p.33. ■ PROFILE_BASIC_OS—The basic OS profile provides a small operating system. It supports a full I/O system, file descriptors, and related ANSI routines. It also supports task and environment variables, signals, pipes, coprocessor management, and the ROMFS file system. This profile is close to a VxWorks 5.5 configuration, but without the network stack and debugging assistance tools. It can also be viewed as a lightweight version of the default VxWorks 6.x configuration, but without memory protection, the network stack, System Viewer instrumentation, and debugging assistance support (the WDB target agent). For more information, see Basic OS Profile, p.35. Each of the small VxWorks profiles produce an operating system that is smaller than the current default VxWorks 6.x configuration. The smallest configuration can build an image of 100 KB or less. The profiles are not monolithic. Each can be used as a base upon which additional functionality can be added with other VxWorks components, using standard configuration facilities (Workbench and vxprj). Custom facilities and applications can also be added, as with VxWorks configurations based on components and other profiles. And, additional measures—such as static instantiation of objects—can be used to keep the system as lean and efficient as possible. Figure 2-1 illustrates the relationship between the three profiles and the functionality they provide. 24 2 Kernel 2.4 VxWorks Configuration NOTE: The small VxWorks profiles are built from source code, so you must install VxWorks source to use them. For this release they can only be built with the Wind River compiler. NOTE: For this release, the small VxWorks profiles are not available for all BSPs. They are provided for wrSbcPowerQuiccII (for PowerPC) and integrator1136jfs (for ARM). How Small Configuration Profiles Create Smaller Systems The PROFILE_MINIMAL_KERNEL, PROFILE_BASIC_KERNEL, and PROFILE_BASIC_OS profiles all produce systems that are smaller than those that can be created from standard VxWorks components. They can do so because they are build from conditionally-compiled source code, which selectively eliminates code from individual components that is not strictly required for the level of functionality that each profile provides (as, for example, is done with taskLib). Standard VxWorks components on the other hand, are provided as pre-compiled libraries, which are linked into a system by way of symbolic references. This method is convenient, and provides for quick builds, but it means that components tend to somewhat larger and more general purpose than suits the needs of systems with very tight requirements for size and functionary. Small configuration profiles allow for building systems that are scaled down to smaller sizes in a simple, predetermined manner. Each provides a subset of the features—and in some cases elements of standard features—that are provided in in the default VxWorks configuration. The small configuration profiles also provide improved system performance, because they only include code that is carefully tailored to the requirements of the system. 25 2 VxWorks Kernel Programmer's Guide, 6.6 Figure 2-1 Small VxWorks Configuration Profiles Basic OS Full I/O system select( ) support Full-formatted I/O ANSI stdio ANSI stdlib ANSI time TTY driver Full-featured drivers Full-featured memory allocator Coprocessor support Floating-point support Signals Pipes Basic Kernel Basic I/O system Dynamic memory allocation/deallocation Dynamic object creation/deletion Message queues Exception task Task hooks Task restart capability Minimal Kernel Interrupts System clock Simple drivers Cache support ANSI ctype, string Static allocation of system resources 26 Multitasking Watchdogs Semaphores Exception handling Events 2 Kernel 2.4 VxWorks Configuration Configuring and Building Small VxWorks Configurations The small VxWorks profiles are built from source code, so you must install VxWorks source to use them. You must also create a project using the appropriate configuration profile and select the option for building from source. For the vxprj command-line tool, use the -source option; for Workbench, select the source build option during project creation. Each small VxWorks profile has a predefined set of components that belong to it. If you choose to change the default configuration of a profile, you should be aware of the following guidelines and behavior: ! ■ If components are not needed, they can be removed. ■ If a component that is used in a higher-level profile is added, the profile is automatically elevated to the next level that uses the component. For example, if you add a message queue component to the PROFILE_MINIMAL_KERNEL profile the project is automatically expanded to the PROFILE_BASIC_KERNEL profile, with all the components provided by that profile. ■ If you add components that are intended to be used with any of the (source) small profiles—such as networking components—the project defaults to using the standard binary components. In effect, the advantage of using a small VxWorks profile is lost. CAUTION: In order to maintain a small VxWorks configuration profile for a project, you must be careful with adding other components. Adding components that are not part of one of these profiles causes the project to use the default binary components, and produces a larger system with different functionality (even on a per-component basis) than the profile you started with. Optimization of Small VxWorks Profile Systems Systems produced with small VxWorks profiles can be further optimized when code is developed using the following methods: ■ Static instantiation of kernel objects—which is required for PROFILE_MINIMAL_KERNEL applications—can be useful with the other profiles as well. For information in this regard, see 2.6.4 Static Instantiation of Kernel Objects, p.56. 27 2 VxWorks Kernel Programmer's Guide, 6.6 ■ Using the VX_GLOBAL_NO_STACK_FILL configuration parameter disables stack filling on all tasks in the system (for information about the parameter, see Filling Task Stacks, p.175). Minimal Kernel Profile The minimal kernel profile (PROFILE_MINIMAL_KERNEL) provides the most basic level at which a VxWorks system can operate. This profile consists of the micro-kernel and basic support code for the CPU and BSP. The profile provides multitasking and interrupt management at a very minimum. Support for semaphores (binary, counting, and mutexes) and watchdogs is also present, but is optional (that is, it can be removed). A subset of the ANSI C library is available in the minimal kernel profile. These include support for ctype, string manipulation, and routines converting numbers to strings and vice versa. The minimal kernel profile does not provide an I/O system or mechanisms for dynamic memory allocation. The profile provides the foundation for small statically-resourced kernel applications, such as small fixed-function controller types of systems that are traditionally implemented using micro-controllers. Statically-resourced systems are systems in which all application and kernel entities are pre-allocated by the compiler at system build time. There are no memory allocations done at run-time. Therefore minimal kernel systems spend less time initializing themselves, and have no chance of resource unavailability. There is a much higher level of determinism in these systems because resources are guaranteed to be available as soon as the system boots. All the application need do is to initialize the storage appropriately before it is ready for business. Static instantiation of kernel objects are explained in detail in 2.6.4 Static Instantiation of Kernel Objects, p.56. Static instantiation of system resources does have its own shortcomings. It is not suitable for systems that are inherently dynamic in nature, that is, ones that have widely differing amounts of loads, or those that must instantiate and destroy objects on demand. Statically-resourced systems therefore are not suitable for all types of applications. Static Memory Allocation A unique characteristic of the minimal kernel profile is that it requires static memory allocation; that is, all memory allocation must occur at compile time. There is no support for dynamic memory allocation (that is, malloc( ), free( ), and 28 2 Kernel 2.4 VxWorks Configuration related routines are not supported). Both system and application components are expected to declare storage for all objects at compile time (that is, statically). The absence of dynamic allocation in this profile also implies that the kernel cannot dynamically instantiate objects like tasks, semaphores and watchdogs. APIs such as taskSpawn( ), taskDelete( ), semXCreate( ), semDelete( ), and so on, are not available. However the same kind of objects can be instantiated statically. Unsupported Facilities The minimal kernel profile is a very small, limited environment that is suitable only for small, fixed-function systems. Consequently, it is also a very limited programming environment. Significant capabilities that are absent from a minimal kernel, which would otherwise be present in more feature rich configurations of VxWorks. These features are as follows: ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ Dynamic memory allocation and de-allocation. The ability to destroy or terminate kernel objects. Memory protection (that is, detection of null pointer and other invalid memory accesses). Support for task hooks (that is, taskHookLib). Floating point and other coprocessor support. I/O system. Signals. Processes (RTPs). ISR Objects (that is, isrLib). WDB target agent. Networking. C++ support. System Viewer logging. Device Drivers for Minimal Kernel Systems Since there is no I/O system in this profile, there is no support for traditional device access APIs like open( ), close( ), read( ), write( ), and so on. Device drivers written for such systems must be standalone programs that manage devices directly. DMA-safe buffers (if needed) must be allocated at compile time. Since there is no support for malloc( ) or free( ), there is correspondingly no support for cacheDmaMalloc( ) or cacheDmaFree( ) either. Formatted Character String Output The INCLUDE_FORMATTED_OUT_BASIC component supplies capability for formatted output with routines like printf( ), sprintf( ), snprintf( ), printfExc( ), and so on. In the minimal and basic kernel profiles, these routines are limited to 29 2 VxWorks Kernel Programmer's Guide, 6.6 outputting only integer values and strings. The supported formats are %d, %s, %c, %x, %X, %u, and %o only. Floating point, 64-bit, or vector type formats are not supported with this profile. Because there is no I/O system in the minimal kernel profile, there are no file descriptors, and the assumption that printf( ) output is sent to file descriptor 1 is not true for this profile. The printf( ) routine works for the formats described above, but its output is sent to the console device through a dedicated function. Do not attempt to make use of file descriptors, standard output, or standard error with this profile, because they do not operate in the standard manner. Minimal Kernel Profile Components and Libraries The components and libraries that make up the VxWorks minimal kernel profile are listed in Table 2-2. . Table 2-2 Minimal Kernel Profile Components Component Library Error detection and reporting stub. INCLUDE_EDR_STUB INCLUDE_ANSI_CTYPE Description ansiCtype ANSI ctype routines like isalpha( ), iscntrl( ), isdigit( ), and so on. ANSI bsearch( ) routine INCLUDE_ANSI_BSEARCH INCLUDE_ANSI_STDLIB_NUMBERS ansiStdlib ANSI stdlib string-number conversion routines. INCLUDE_ANSI_STRING ansiString Full set of ANSI string routines. ANSI abs( ) routine. INCLUDE_ANSI_ABS INCLUDE_ANSI_MEMCHR ansiString ANSI memchr( ) routine. INCLUDE_ANSI_MEMCPY ansiString ANSI memcpy( ) routine. INCLUDE_ANSI_MEMSET ansiString ANSI memset( ) routine. INCLUDE_ANSI_MEMCMP ansiString ANSI memcmp( ) routine. INCLUDE_ANSI_MEMMOVE ansiString ANSI memmove( ) routine. INCLUDE_ANSI_STRCAT ansiString ANSI strcat( ) routine. INCLUDE_ANSI_STRNCAT ansiString ANSI strncat( ) routine. 30 2 Kernel 2.4 VxWorks Configuration Table 2-2 Minimal Kernel Profile Components Component Library Description INCLUDE_ANSI_STRCMP ansiString ANSI strcmp( ) routine. INCLUDE_ANSI_STRNCMP ansiString ANSI strncmp( ) routine. INCLUDE_ANSI_STRCPY ansiString ANSI strcpy( ) routine. INCLUDE_ANSI_STRNCPY ansiString ANSI strncpy( ) routine. INCLUDE_ANSI_STRLEN ansiString ANSI strlen( ) routine. INCLUDE_REBOOT_HOOKS rebootLib Support for reboot hooks; that is rebootHookAdd( ). INCLUDE_VXEVENTS eventLib, semEvLib, msgQEvLib VxWorks events support. INCLUDE_SEM_BINARY semBLib Support for binary semaphores. INCLUDE_SEM_MUTEX semMLib Support for mutex semaphores. INCLUDE_SEM_COUNTING semCLib Support for counting semaphores. INCLUDE_TASK_UTIL taskUtilLib Programmatic interface for modifying task information. INCLUDE_WATCHDOGS wdLib Support for watchdog timers. INCLUDE_HOOKS hookLib Hook routine table support. VxWorks traditional scheduler (priority-based preemptive scheduling). INCLUDE_VX_TRADITIONAL_SCHEDULER INCLUDE_FORMATTED_OUT_BASIC 2 fioLib Support for printf( ), sprintf( ), snprintf( ), oprintf( ), and printErr( ) only. No support for scanf( ) and its variants. No support for vprintf( ) or its variants. No support for floating point or vector formats. 31 VxWorks Kernel Programmer's Guide, 6.6 Table 2-2 Minimal Kernel Profile Components Component Library INCLUDE_BOOT_LINE_INIT bootParseLib Parse boot device configuration information 32 Description 2 Kernel 2.4 VxWorks Configuration Basic Kernel Profile The level above the minimal kernel is provided by the basic kernel profile (PROFILE_BASIC_KERNEL). The basic kernel profile produces small VxWorks systems that build on the minimal kernel to provide support for moderately complex applications. Systems based on the basic kernel profile are still not much more than a kernel But in addition to the a minimal kernel system, the basic kernel profile offers support for the following facilities: ■ ■ ■ ■ ■ ■ Basic I/O system Inter-task communication using message queues. Support for task hooks. Memory allocation and free (using memPartLib). Ability to dynamically create and delete kernel objects such as tasks, semaphores, watchdogs and message queues (enabled by memPartLib). Support for ANSI string routine strdup( ), which relies on malloc( ). The most notable additions to this profile are support for basic I/O facilities, support for message queues and task hooks, and support for memory allocation and de-allocation. This allows applications based on this profile to be more dynamic and feature-rich than the minimal kernel. What this profile provides, however, is still a kernel and not an operating system. It has a full complement of intertask communications mechanisms and other kernel features, but does not have operating system capabilities such as memory protection, file system support, or higher-level constructs such as pipes and so on. Device Drivers for Basic Kernel Systems Like the minimal kernel profile, there is no I/O system present in the basic kernel profile. Hence device drivers for such systems must be standalone programs, managing devices directly. Since malloc( ) and free( ) are supported, cacheDmaMalloc( ) and cacheDmaFree( ) are available starting with this profile. Formatted Character String Output The very same limitations on formatted output apply to the basic kernel profile, as are present for the minimal kernel profile. See Formatted Character String Output, p.29. Basic Kernel Profile Components and Libraries In addition to the components and libraries provided by the minimal kernel profile (listed in Table 2-2), the basic kernel profile provides those listed in Table 2-3. 33 2 VxWorks Kernel Programmer's Guide, 6.6 Table 2-3 Basic Kernel Profile Components—in Addition to Minimal Kernel Profile Component Library Description INCLUDE_ANSI_STRDUP ansiString ANSI strdup( ) routine. INCLUDE_TASK_CREATE_DELETE taskLib Support for taskSpawn( ), taskCreate( ), taskDelete( ) and exit( ). INCLUDE_TASK_RESTART taskLib Support for taskRestart( ). INCLUDE_EXC_TASK excLib Support for excJobAdd( ). INCLUDE_ISR_OBJECTS isrLib Interrupt service routine objects library. INCLUDE_MSG_Q msgQLib Message queue support with msgQInitialize( ), msgQReceive( ), msgQSend( ) and so on. INCLUDE_MSG_Q_CREATE_DELETE msgQLib Message queue creation and deletion support with msgQCreate( ) and msgQDelete( ). Support for msgQInfoGet( ). INCLUDE_MSG_Q_INFO INCLUDE_SEM_DELETE semLib Support for semaphore deletion with semDelete( ). INCLUDE_SEM_BINARY_CREATE semBLib Support for semBCreate( ). INCLUDE_SEM_COUNTING_CREATE semCLib Support for semCCreate( ). INCLUDE_SEM_MUTEX_CREATE semMLib Support for semMCreate( ). INCLUDE_SEM_INFO Support for semInfo( ). INCLUDE_TASK_INFO Support for taskInfoGet( ). INCLUDE_TASK_HOOKS taskHookLib Support for adding/removing hook routines at task creation, deletion and task switches. INCLUDE_WATCHDOGS_CREATE_DELETE wdLib 34 Support for wdCreate( ) and wdDelete( ). 2 Kernel 2.4 VxWorks Configuration Table 2-3 Basic Kernel Profile Components—in Addition to Minimal Kernel Profile Component Library INCLUDE_MEM_MGR_BASIC memPartLib Memory partition manager; malloc( ), free( ) realloc( ). INCLUDE_HASH hashLib Hash table management library. INCLUDE_LSTLIB lstLib Doubly linked list subroutine library. INCLUDE_RNG_BUF rngLib Ring buffer management library. INCLUDE_POOL poolLib Memory pool management library. INCLUDE_IO_BASIC Description 2 Basic I/O functionality. Basic OS Profile The basic OS profile (PROFILE_BASIC_OS) builds upon the basic kernel profile to offer a relatively simple real-time operating system. It does not, for example, provide support for networking or real-time processes (RTPs). This configuration is similar to a VxWorks 5.5 configuration, but without the network stack and debugging assistance tools (the WDB target agent). The profile provides an operating system instead of simply a kernel. The new capabilities added in this profile are the following: ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ Full I/O system, which includes file system and POSIX support. Standard I/O file descriptors and associated API support. APIs for directory and path manipulations, and disk utilities. Support for select( ). TTY and pipe driver support. Support for logging (logLib). Support for task and environment variables (envLib, taskVarLib). Support for coprocessor management (coprocLib) and floating point. Full-featured memory partition manager (memLib). Full ANSI library support. Adds support for assert( ), setjmp( ) and longjmp( ), stdio, stdlib, and time library routines. Device Drivers for Basic OS Systems Device drivers for the basic OS can now use additional IO system features, associated capabilities like select( ), and so on. File descriptor based I/O and 35 VxWorks Kernel Programmer's Guide, 6.6 associated APIs are available. Another major addition is coprocessor support, which typically provides support for hardware floating point operations. Vector operations (for some PowerPC BSPs) are also available with the coprocessor support infrastructure (coprocLib). More advanced ANSI routines are available, that use the standard I/O system, ANSI time facilities and mathematical routines. Formatted Character String Output Full ANSI formatted I/O routines are available starting with the basic OS profile. Formatted output routines like printf( ), sprintf( ), and so on can handle floating point or vector types if applicable. Formatted input routines such as scanf( ) and so on are also available. These routines send their output to the standard I/O file descriptors as expected. These capabilities are available with the INCLUDE_FORMATTED_IO component. Basic OS Profile Components and Libraries In addition to the components and libraries provided by the minimal kernel profile and basic kernel profile (listed in Table 2-2 and Table 2-3), the basic OS profile provides those listed in Table 2-4. 36 2 Kernel 2.4 VxWorks Configuration Table 2-4 Basic OS Profile Components—in Addition to the Minimal and Basic Kernel Profiles 2 Component Library Description INCLUDE_ANSI_ASSERT ansiAssert ANSI assert( ) routine. INCLUDE_ANSI_LOCALE ansiLocale ANSI locale routines localeconv( ) and setlocale( ). INCLUDE_ANSI_LONGJMP ansiSetjmp ANSI setjmp( ) and longjmp( ) routines. INCLUDE_ANSI_MATH ansiMath ANSI math routines. INCLUDE_ANSI_STDIO ansiStdio ANSI stdio routines. INCLUDE_ANSI_STDLIB ansiStdlib ANSI stdlib routines. INCLUDE_ANSI_ABORT ansiStdlib ANSI abort( ) routine. INCLUDE_ANSI_TIME ansiTime ANSI time routines INCLUDE_ANSI_STRERROR ansiStdio ANSI strerror( ) routine. INCLUDE_POSIX_CLOCKS clockLib POSIX clock library support for clock_getres( ), clock_setres( ), clock_gettime( ) and clock_settime( ). INCLUDE_ENV_VARS envLib Environment variable library; getenv( ), setenv( ) and so on. INCLUDE_TASK_VARS taskVarLib Task variables support library; taskVarAdd( ), taskVarDelete( ), taskVarGet( ), taskVarSet( ) and so on. INCLUDE_SIGNALS sigLib Software signal library; support for signal( ), kill( ) and so on. Error detection and reporting persistent memory region manager. INCLUDE_EDR_PM INCLUDE_TTY_DEV ttyLib TTY device driver. INCLUDE_FLOATING_POINT floatLib Floating point scanning and formatting library. INCLUDE_FORMATTED_IO fioLib Full formatted I/O support; printf( ), scanf( ), and variants. 37 VxWorks Kernel Programmer's Guide, 6.6 Table 2-4 Basic OS Profile Components—in Addition to the Minimal and Basic Kernel Profiles Component Library Description INCLUDE_POSIX_FS fsPxLib POSIX APIs for file systems. INCLUDE_IO_SYSTEM ioLib, iosLib dirLib, pathLib I/O system and associated interfaces. Directory and path manipulation API’s. For more information, see 7.2 Configuring VxWorks With I/O Facilities, p.362). INCLUDE_LOGGING logLib Message logging support; logMsg( ), logFdSet( ) and so on. INCLUDE_MEM_MGR_FULL memLib Support for calloc( ), valloc( ), realloc( ) and so on. INCLUDE_PIPES pipeDrv Pipe device support. INCLUDE_TYLIB tyLib TTY driver support library. ROMFS (read-only memory based file system ). INCLUDE_ROMFS INCLUDE_SELECT selectLib Support for select( ) and associated API’s. INCLUDE_STDIO stdioLib Support for stdioFp( ). 38 2 Kernel 2.4 VxWorks Configuration 2.4.6 Customizing VxWorks Code VxWorks operating system code can itself be customized. This section introduces customization of usrClock( ), hardware initialization, and more general features of the operating system. System Clock Modification During system initialization at boot time, the system clock ISR—usrClock( )—is attached to the system clock timer interrupt. For every system clock interrupt, usrClock( ) is called to update the system tick counter and to run the scheduler. You can add application-specific processing to usrClock( ). However, you should keep in mind that this is executed in interrupt context, so only limited functions can be safely called. See 4.20.5 Special Limitations of ISRs, p.245 for a list of routines that can be safely used in interrupt context. Long power management, if used, allows the processor to sleep for multiple ticks. See 2.5 Power Management, p.40. The usrClock( ) routine, and therefore tickAnnounce( ), is not called while the processor is sleeping. Instead, usrClock( ) is called only once, after the processor wakes, if at least one tick has expired. Application code in usrClock( ) must verify the tick counter each time it is called, to avoid losing time due to setting the processor into sleep mode. Hardware Initialization Customization When the application requires custom hardware, or when the application requires custom initialization of the existing hardware, the BSP must be modified to perform the initialization as required. What BSP modifications are required depend on the type of hardware and the type of initialization that must be performed. For information about adding or customizing device drivers, the VxWorks Device Driver Developer’s Guide, specifically the introductory sections. For information about custom modifications to BSP code, see the VxWorks BSP Developer’s Guide. Other Customization The directory installDir/vxworks-6.x/target/src/usr contains the source code for certain portions of VxWorks that you may wish to customize. For example, 39 2 VxWorks Kernel Programmer's Guide, 6.6 usrLib.c is a common place to add target-resident routines that provide application-specific development aids. If you modify one of these files, an extra step is necessary before rebuilding your VxWorks image: you must replace the modified object code in the appropriate VxWorks archive. The makefile in installDir/vxworks-6.x/target/src/usr automates the details. This directory is not specific to a single architecture, however, so you must specify the value of the CPU variable with make on the command line, as follows: c:\installDir\vxworks-6.x\target\src\usr> make CPU=cputype TOOL=tool This step recompiles all modified files in the directory, and replaces the corresponding object code in the appropriate architecture-dependent directory. After that, the next time you rebuild VxWorks, the resulting system image includes your modified code. The following example illustrates replacing usrLib with a modified version, rebuilding the archives, and then rebuilding the VxWorks system image. For the sake of conciseness, the make output is not shown. The example assumes the pcPentium BSP; replace the BSP directory name and CPU value as appropriate for your environment. c:\> cd installDir\vxworks-6.1\target\src\usr c:\installDir\vxworks-6.1\target\src\usr> copy usrLib.c usrLib.c.orig c:\installDir\vxworks-6.1\target\src\usr> copy develDir\usrLib.c usrLib.c c:\installDir\vxworks-6.1\target\src\usr> make CPU=PENTIUM TOOL=diab ... c:\installDir\vxworks-6.1\target\src\usr> cd nstallDir\vxworks-6.1\target\config\pcPentium c:\installDir\vxworks-6.1\target\config\pcPentium2> make ... 2.5 Power Management Starting with the VxWorks 6.2 release, enhanced power management facilities are provided for the Intel Architecture (IA). Facilities provided in earlier releases for other architectures remain the same. The new facilities will be provided for the other architectures in future releases. See 2.5.1 Power Management for IA Architecture, p.41 and 2.5.2 Power Management for Other Architectures, p.49. 40 2 Kernel 2.5 Power Management 2.5.1 Power Management for IA Architecture VxWorks power management facilities provide for managing the power and performance states of the CPU. These facilities can be used to control CPU power use based on the following: ■ ■ ■ CPU utilization CPU temperature thresholds task and ISR-specific performance states The VxWorks power management facilities utilize key concepts of the Advanced Configuration and Power Interface (ACPI) Specification, version 3.0. The ACPI specification has not been implemented for VxWorks because of its unsuitability for hard real-time systems and for all the architectures supported by VxWorks. However, the ACPI specification provides useful definitions of power states and power-state transitions, as well as of thermal management, and these definitions have been incorporated into the design of the VxWorks power management facilities. ACPI Processor Power and Performance States The ACPI 3.0 specification defines processor power states as well as the transitions that take the processor from one state to the other. Essentially it defines the processor power state machine. This aspect of the specification enables the mapping of the power management features of a CPU to one of the defined states, whether the CPU is ACPI compliant or not. For example, ACPI defines that in power state C1, the processor does not execute instructions but the contents of the caches remain valid (bus snooping still takes place). Many CPUs support such a power state, but manufacturers often use different names to identify that state. In addition to defining processor power states, ACPI defines performance states where the CPU executes instructions, but not necessarily at its maximum throughput. These states correspond to voltage and or frequency scaling capabilities present on some CPUs, and provide a power management scheme with which power can be managed even if the system is not idle. Figure 2-2 illustrates the ACPI-defined power states that apply to the CPU power management for VxWorks. 41 2 VxWorks Kernel Programmer's Guide, 6.6 Figure 2-2 Fig 2-2: ACPI Power States G0 Global System State C0 Processor Power State Increased Latency, Increased Power Savings P0 Processor Performance State C1 Processor Power State Decreased Performance, Increased Power Savings P1 Processor Performance State Cn Processor Power State Pn Processor Performance State The G0 global system state is also known as the working state. ACPI requires that all processor power states reside under the G0 state, which is why other G states are not deemed relevant to this feature. The C0 to Cn states are processor power states. Key features of these processor power are as follows: ■ In the C0 state the processor is fetching and executing instructions ■ In the C1 to Cn states the processor is not executing instructions. ■ The higher the power state number, the greater the power saving, but at the cost greater latency in reaction to external events. ■ State transitions occur to and from the C0 state. For example, after going from the C0 state to the C1 state the processor must transition back to the C0 state before going to the C2 state. This is because transitions are triggered by software and only the C0 state is allowed to execute instructions. Under the C0 power state reside the processor performance states. In each of these states the CPU is executing instructions but the performance and power savings in each P-state vary. The higher the performance state number, the greater the power saving, but the slower the rate of instruction execution. Taking the Speedstep technology of the Pentium processor as an example, it defines various voltage-frequency power settings that are mapped to the ACPI-defined P-states. Note that unlike the C-state transitions, P-state transitions can occur between any two states. 42 2 Kernel 2.5 Power Management See the VxWorks Architecture Supplement for information about which states are supported 2 ACPI Thermal Management Much like the processor power management concepts, the thermal management concepts defined in ACPI 3.0 are applicable to non ACPI-compliant hardware. Some of these concepts are: ■ Differentiation between active cooling and passive cooling. Actively cooling a system consists of activating a cooling device such as a fan. Passive cooling is achieved by reducing the power consumed by a device. In this case device includes processors and therefore this is relevant to this feature. ■ Critical Shut Down. It is the temperature threshold at which a device or system is shut down so as to protect it from heat induced damages. ■ Notification of temperature changes. This allows a power management entity to actively or passively manage the temperature of a system or device without the need to poll the devices to obtain their operating temperature. ■ Processor Throttling. This is the link between thermal management and the processor power states. ACPI equations define how to manage the performance states of a processor so as to attempt to keep it inside a temperature zone. VxWorks Power Management Facilities The architecture of the VxWorks power management facilities is composed of two basic elements: a power management framework and a power manager. The power management framework is effectively a layer between the power manager and the CPU. It transfers status information from the CPU to the power manager, and executes control of the CPU based on instructions from the power manager. Figure 2-3 illustrates this relationship. 43 VxWorks Kernel Programmer's Guide, 6.6 Figure 2-3 Fig 2-3: Power Management Architecture Power Manager events status control Power Management Framework events status control CPU The power management framework is designed to accommodate two use cases for controlling power consumption: one minimizes the power level of the CPU based on how much work it has to do (and its temperature); the other runs tasks and ISRs at different performance states based on their priority. Wind River provides the power management framework and a two power managers—only one of which can be used at a time (see Wind River Power Managers, p.47). You can develop your own power manager for either of the two use cases supported by the power management framework (see Power Management Framework and Use Cases, p.44). The APIs provided by the power management framework give you the control mechanisms for a power manager (see Power Management Framework API, p.48). Power Management Framework and Use Cases The VxWorks power management framework is designed to serve two use cases: one bases the control of power consumption on how much work must be done; and the other bases the control of power consumption on task-specific performance states. One use case involves controlling the power consumed by the CPU based on how much work the CPU has to do. The idea is to keep the power level of the CPU as low as possible while preventing the system from going into overload. That is, prevent running at 100% CPU utilization for a user-defined period of time. It is 44 2 Kernel 2.5 Power Management quite clear that the writers of the ACPI specification had this use case in mind while writing the document. The second use case is based on the premise that power can be controlled by having tasks and ISRs execute at different performance states (P-states). For example, a task that performs work queued up by interrupts may need to run at the P0 performance state (highest performance) while a maintenance task with no hard deadlines can afford to run at the lowest performance state. The first use case is more global in nature in that the entire system is running in a certain power state. It is also a scenario in which the power consumption is dynamically adapted to the work that is required of the processor. One of the drawback of the approach however is that it makes it difficult to guarantee deadlines can be met, as a piece of code is not guaranteed to run in the same performance state on every invocation. The second use case provides a finer granularity of control and can be more deterministic, since each task can be set to run in the same performance state at all times. This comes at the price of increased context switching and interrupt handling times. NOTE: While the power management framework allows for various power management methods to be used, the power manager itself must be designed to ensure that it uses the capacities of the framework in a coherent manner. For example, the framework cannot prevent contention for the CPU if both of the use cases described above are implemented at the same time. For the same reason, only one power manager should be included in the configuration of VxWorks (the two power managers provided by Wind River are mutually exclusive of one another). CPU Utilization Based Power Management A CPU utilization based power manager is one that uses CPU utilization and CPU temperature to control the power consumption of the CPU. There are really two aspects to this approach. One is to transition the CPU from the C0 power state (executing state) to one of the other C-states (non-executing states) when the VxWorks kernel becomes idle. The other aspect is to control the performance state (P-state) of the CPU so as to keep it inside a specified range of CPU utilization and, optionally, inside a temperature range. In order to support a power manager using this approach, the power management framework has the following features: ■ The framework notifies the power manager when the VxWorks kernel goes idle. ■ The framework notifies the power manager when the VxWorks kernel comes out of idle state. 45 2 VxWorks Kernel Programmer's Guide, 6.6 ■ The framework allows the power manager to transition the CPU from the C0 state to any of the non-executing power states: C1, C2, ...Cn. Note that the transition back to the C0 state occurs when an external event takes place (that is, an interrupt) and therefore this is not a state transition the framework can allow the power manager to perform/control. ■ The framework allows the power manager to transition the CPU between performance states (P-states) based on the CPU utilization over a user-defined time interval. This is achieved by the framework keeping track of CPU utilization and reporting that figure to the power manager. ■ The framework computes the CPU utilization over two user-specified time intervals. Having two intervals makes it easier for the power manager to implement a quick ramp up, slow ramp down policy through the performance states. The sampling intervals can be modified dynamically. ■ The framework notifies the power manager when a CPU-utilization interval has elapsed and provides the CPU utilization figure to the power manager at that time. ■ The framework allows the power manager to specify a high and a low temperature threshold for the purpose of being notified whenever the temperature of the CPU crosses either threshold. These thresholds can be modified dynamically. The purpose for these is to allow the power manager to implement a cooling policy such as reducing the CPU performance state to lower power consumption, hence lowering temperature. The full-featured CPU utilization power manager provided by Wind River is an example of this type of power management. See Wind River Power Managers, p.47. Task Performance-Based Power Management The per-task performance power manager is based on the premise that power can be controlled by having tasks execute at different performance states (P-states). For example, a task that performs work queued up by interrupts may need to run at the P0 performance state (highest performance) while a maintenance task with no hard deadlines can afford to run at the lowest performance state. In order to support a power manager using this approach, the power management framework has the following features: ■ The framework allows a performance state (P-state) to be assigned to each task and allows that state to be set during context switches. ■ The framework allows a single performance state to be assigned for all interrupts in the system so that execution of ISRs can be performed in a performance state other than the one of the interrupted task. 46 2 Kernel 2.5 Power Management Wind River Power Managers Wind River provides two power managers that implement CPU-utilization-based power management: ■ A full-featured CPU-utilization-based power manager. It manages the C-state of the CPU when VxWorks goes idle, as well as managing the P-state of the CPU based on CPU utilization. See CPU Utilization Based Power Management, p.45. ■ A light version of a CPU-utilization-based power manager, which simply manages the C-state of the CPU when VxWorks goes idle. It implements the same power management algorithm that was provided for VxWorks 6.0 and 6.1; and is included in the default configuration of VxWorks configuration so that the power management behavior of the operating system is the same as in versions prior to 6.2. See 2.5.2 Power Management for Other Architectures, p.49 for more information about its features. The components used to configure VxWorks with these power managers are listed in Configuring VxWorks With Power Management Facilities, p.49. 47 2 VxWorks Kernel Programmer's Guide, 6.6 Power Management Framework API Table 2-5 describes the API provided by the power management framework. Power managers use this API to plug into the framework. The routines are available only in the kernel. Table 2-5 Power Management Framework API Routine Description cpuPwrCStateSet( ) Sets the CPU in a specified power state (C-state). cpuPwrPStateSet( ) Sets the CPU in a specified performance state (P-state). cpuPwrPStateGet( ) Returns the performance (P-state) state of the CPU. cpuPwrTaskPStateSet( ) Sets the performance state (P-state) of a task. cpuPwrTaskPStateGet( ) Gets the performance state (P-state) of a task. cpuPwrTempThreshSet( ) Sets the CPU temperature thresholds for the CPU (high and low). cpuPwrTempThreshGet( ) Returns the temperature thresholds for the CPU. cpuPwrUtilPeriodSet( ) Sets the two time intervals over which CPU utilization is computed. cpuPwrEventHandlersSet( ) Registers a set of handlers for the various power management events. For more information about the routines and the power states supported with VxWorks, see the API reference for cpuPwrLib. Also see the VxWorks Architecture Supplement for the mappings between the ACPI specification C-states and P-states and the power modes supported by the CPU in question. 48 2 Kernel 2.5 Power Management Configuring VxWorks With Power Management Facilities Configure VxWorks with the INCLUDE_CPU_PWR_MGMT component for the power management framework. Use one of the power manager components provided by Wind River: ■ ■ INCLUDE_CPU_UTIL_PWR_MGR, which is full-featured CPU-utilization-based power manager. INCLUDE_CPU_LIGHT_PWR_MGR, which is a light version of a CPU-utilization-based power manager. For full descriptions of these power managers, see Wind River Power Managers, p.47. A custom power manager can be used in place of a Wind River power manager. It can be included as an application module or a custom component. For more information, see 2.6.8 Linking Kernel Application Object Modules with VxWorks, p.64 and 2.8 Custom VxWorks Components and CDFs, p.67. Power Management and System Performance Performance is a concern for the CPU power management framework because it interfaces to the interrupt handling and scheduling sub-systems in a way that affects the interrupt latency and the task context switch time. 2.5.2 Power Management for Other Architectures NOTE: For this release, the power management facilities available for architectures other than IA are the same as provided for VxWorks 6.0 and 6.1. These facilities are described in this section. The features described in 2.5.1 Power Management for IA Architecture, p.41 will be available for other architectures in future releases. Power management allows the processor to conserve power by entering a low power state. While in this mode, processor register values and memory contents are retained. This feature is implemented by putting the CPU in a non-executing state while the kernel is idle. This has no impact on the operation of peripheral devices except for the system timer when long sleep mode (described below) is selected. The VxWorks power management facilities provide two modes of operation: 49 2 VxWorks Kernel Programmer's Guide, 6.6 ■ Short Sleep Mode In short sleep mode, the CPU is put in a low power state until the next interrupt occurs, including the system clock interrupt. The maximum amount of time the CPU can sleep is therefore the interval in between system clock interrupts. The short sleep mode does not require special BSP support. It is provided at the architecture level. See the VxWorks Architecture Supplement to determine if this mode is supported for your CPU. ■ Long Sleep Mode In long sleep mode, the CPU is put in a low power state until the next interrupt occurs, excluding the system clock interrupt. This allows the CPU to sleep until the next system event is scheduled to occur; such as a task that times out on a semaphore take operation or a watchdog that fires. This mode requires BSP support because the system clock interrupt source must be turned off, and a mechanism must schedule the CPU to wake after a specified amount of time. To provide power management support for your system, configure VxWorks with the INCLUDE_POWER_MGMT_BSP_SUPPORT component. For more information, see the VxWorks BSP Developer’s Guide. Also see System Clock Modification, p.39. 50 2 Kernel 2.6 Kernel Applications 2.6 Kernel Applications VxWorks applications that execute in the kernel are created as relocatable object modules. They can be referred to most specifically as kernel-based application modules, but it is often convenient to refer to them simply as kernel application modules or kernel applications. In any case, they should not be confused with process-based (RTP) applications. When a kernel-based application module is built, user code is linked to the required VxWorks libraries, and an ELF binary is produced. Kernel applications use VxWorks facilities by including header files that define operating system interfaces and data structures. Kernel application modules can be either: ■ Downloaded and dynamically linked to the operating system by the object module loader. ■ Statically linked to the operating system, making them part of the system image. Downloading kernel modules is useful for rapid development and debugging, as the operating system image does not need to be rebuilt for each iteration of the application. This method can also be used for diagnostic facilities with production systems. Various development tools, including the debugger and the shell (host or kernel), can be used to download and manage modules. Modules can be downloaded to a target from any host file system for which the kernel has support (NFS, ftp, and so on). Kernel application modules can also be stored on the target itself in flash or ROM, in the ROMFS file system, or on disk. Once they have been loaded into the target, kernel application modules can be started interactively from the shell or Workbench. Application modules that are statically linked to the operating system can be run interactively from the shell or Workbench. VxWorks can also be configured to start them automatically at boot time. Static linking and automatic startup are obviously suitable for production systems. An application that runs in kernel space is not executed as a process; it is simply another set of tasks running in kernel space. The kernel is not protected from any misbehavior that a kernel application might engage in—and the applications are similarly not protected from each other—kernel applications and the kernel run in the same address space in supervisor mode. 51 2 VxWorks Kernel Programmer's Guide, 6.6 Note that VxWorks can also be configured with support for applications that execute in user space as processes. See VxWorks Application Programmer’s Guide: Applications and Processes. ! WARNING: If you wish to port a kernel application to a user-mode application that executes as a real-time process (RTP), you must ensure that it meets the code requirements of an RTP application and is compiled as such. You must also ensure that VxWorks is configured with support for RTPs. For more information, see the VxWorks Application Programmer's Guide: Applications and Processes, and the VxWorks Migration Guide. 2.6.1 C and C++ Libraries Both VxWorks native C libraries, and Dinkum C and C++ libraries, are provided for VxWorks application development. As shown in Table 2-6, VxWorks native libraries are used for C kernel application development, and Dinkum libraries are used in all other cases. Table 2-6 C and C++ Libraries Type of Application C Language C++ Language Kernel-mode application VxWorks native libraries Dinkum C++ and embedded (abridged) C++ libraries User-mode RTP application Dinkum C libraries Dinkum C++ and embedded (abridged) C++ libraries The VxWorks native C libraries provide routines outside the ANSI specification. Note that they provide no support for wide or multi-byte characters. For more information about these libraries, see the VxWorks and Dinkum API references. For more information about C++ facilities, see 13. C++ Development. 2.6.2 Application Structure Kernel application code is similar to common C or C++ applications, with the exception that it does not require a traditional main( ) routine (unlike a VxWorks 52 2 Kernel 2.6 Kernel Applications process-based application). It simply requires an entry point routine that starts all the tasks required to get the application running. 2 NOTE: If your kernel application includes a main( ) routine, do not assume that it will start automatically. Kernel application modules that are downloaded or simply stored in the system image must be started interactively (or be started by another application that is already running). The operating system can also be configured to start applications automatically at boot time (see a2.6.10 Configuring VxWorks to Run Applications Automatically, p.66). The entry-point routine performs any data initialization that is required, and starts all the tasks that the running application uses. For example, a kernel application might have a routine named like myAppStartUp( ), which could look something like this: void myAppStartUp (void) { runFoo(); tidThis = taskSpawn("tThis", 200, 0, STACK_SIZE, (FUNCPTR) thisRoutine,0,0,0,0,0,0,0,0,0,0); tidThat = taskSpawn("tThat", 220, 0, STACK_SIZE, (FUNCPTR) thatRoutine,0,0,0,0,0,0,0,0,0,0); tidAnother = taskSpawn("tAnother", 230, 0, STACK_SIZE, (FUNCPTR) anotherRoutine,0,0,0,0,0,0,0,0,0,0); return (OK); } For information about VxWorks tasks and multitasking, see 4. Multitasking. For information about working with C++ see 13. C++ Development. 2.6.3 VxWorks Header Files Many kernel applications make use of VxWorks operating system facilities or utility libraries. This usually requires that the source module refer to VxWorks header files. The following sections discuss the use of VxWorks header files. VxWorks header files supply ANSI C function prototype declarations for all global VxWorks routines. VxWorks provides all header files specified by the ANSI X3.159-1989 standard. VxWorks system header files are in the directory installDir/vxworks-6.x/target/h and its subdirectories. 53 VxWorks Kernel Programmer's Guide, 6.6 VxWorks Header File: vxWorks.h The header file vxWorks.h must be included first by every kernel application module that uses VxWorks facilities. It contains many basic definitions and types that are used extensively by other VxWorks modules. Many other VxWorks header files require these definitions. Include vxWorks.h with the following line: #includeOther VxWorks Header Files Kernel applications can include other VxWorks header files, as needed, to access VxWorks facilities. For example, a module that uses the VxWorks linked-list subroutine library must include the lstLib.h file with the following line: #include The API reference entry for each library lists all header files necessary to use that library. ANSI Header Files All ANSI-specified header files are included in VxWorks. Those that are compiler-independent or more VxWorks-specific are provided in installDir/vxworks-6.x/target/h while a few that are compiler-dependent (for example stddef.h and stdarg.h) are provided by the compiler installation. Each toolchain knows how to find its own internal headers; no special compile flags are needed. ANSI C++ Header Files Each compiler has its own C++ libraries and C++ headers (such as iostream and new). The C++ headers are located in the compiler installation directory rather than in installDir/vxworks-6.x/target/h. No special flags are required to enable the compilers to find these headers. For more information about C++ development, see 13. C++ Development. NOTE: In releases prior to VxWorks 5.5, Wind River recommended the use of the flag -nostdinc. This flag should not be used with the current release since it prevents the compilers from finding headers such as stddef.h. The -I Compiler Flag By default, the compiler searches for header files first in the directory of the source module and then in its internal subdirectories. In general, installDir/vxworks-6.x/target/h should always be searched before the compilers’ 54 2 Kernel 2.6 Kernel Applications other internal subdirectories; to ensure this, always use the following flag for compiling under VxWorks: 2 -I %WIND_BASE%/target/h %WIND_BASE%/target/h/wrn/coreip Some header files are located in subdirectories. To refer to header files in these subdirectories, be sure to specify the subdirectory name in the include statement, so that the files can be located with a single -I specifier. For example: #include #include VxWorks Nested Header Files Some VxWorks facilities make use of other, lower-level VxWorks facilities. For example, the tty management facility uses the ring buffer subroutine library. The tty header file tyLib.h uses definitions that are supplied by the ring buffer header file rngLib.h. It would be inconvenient to require you to be aware of such include-file interdependencies and ordering. Instead, all VxWorks header files explicitly include all prerequisite header files. Thus, tyLib.h itself contains an include of rngLib.h. (The one exception is the basic VxWorks header file vxWorks.h, which all other header files assume is already included.) Generally, explicit inclusion of prerequisite header files can pose a problem: a header file could get included more than once and generate fatal compilation errors (because the C preprocessor regards duplicate definitions as potential sources of conflict). However, all VxWorks header files contain conditional compilation statements and definitions that ensure that their text is included only once, no matter how many times they are specified by include statements. Thus, a kernel application module can include just those header files it needs directly, without regard to interdependencies or ordering, and no conflicts will arise. VxWorks Private Header Files Some elements of VxWorks are internal details that may change and so should not be referenced in a kernel application. The only supported uses of a module’s facilities are through the public definitions in the header file, and through the module’s subroutine interfaces. Your adherence ensures that your application code is not affected by internal changes in the implementation of a VxWorks module. Some header files mark internal details using HIDDEN comments: /* HIDDEN */ ... /* END HIDDEN */ 55 VxWorks Kernel Programmer's Guide, 6.6 Internal details are also hidden with private header files: files that are stored in the directory installDir/vxworks-6.x/target/h/private. The naming conventions for these files parallel those in installDir/vxworks-6.x/target/h with the library name followed by P.h. For example, the private header file for semLib is installDir/vxworks-6.x/target/h/private/semLibP.h. 2.6.4 Static Instantiation of Kernel Objects The VxWorks APIs have a long established convention for the creation and deletion of kernel entities. Objects such as tasks, semaphores, message queues and watchdogs are instantiated using their respective creation APIs (for example, taskSpawn( ), semXCreate( ), and so on) and deleted using their respective delete APIs (for example, msgQDelete( ), wdDelete( ), and so on.). Object creation is a two-step process: first the memory for the object is allocated from the system, which is then initialized appropriately before the object is considered usable. Object deletion involves invalidation of the object, followed by freeing its memory back to the system. Thus, object creation and deletion are dependent on dynamic memory allocation, usually through the malloc( ) and free( ) routines. Dynamic creation and deletion of objects at run-time is a convenient programming paradigm, though it has certain disadvantages for some real-time critical applications. First, the allocation of memory from the system cannot always be guaranteed. Should the system run out of memory the application cannot create the resources it must have function. The application must then resort to a suitable error recovery process if any exists, or abort in some fashion. Second, dynamic allocation of memory is a relatively slow operation that may potentially block the calling task. This makes dynamic allocation non-deterministic in performance. Static instantiation of objects is a faster, more deterministic alternative to dynamic creation. In static instantiation, the object is declared as a compile time variable. Thus the compiler allocates storage for the object in the program being compiled. No more allocation need be done. At run-time the objects memory is available immediately at startup for the initialization step. Initialization of pre-allocated memory is much more deterministic and faster than dynamic creation. Such static declaration of objects cannot fail, unless the program itself is too large to fit in the systems memory. Many applications are suited to exploit static instantiation of objects in varying degrees. Most applications require some resources to be created, that last for the lifetime of the application. These resources are never deleted. In lieu of the latter, objects that last for the lifetime of the application are ideally suited for static (that is, compile time) allocation. To the extent that they are instantiated statically 56 2 Kernel 2.6 Kernel Applications (which we shall see below), the application is that much more fail safe and fast to launch. See 2.4.5 Small VxWorks Configuration Profiles, p.24 for information about operating system profiles of particular relevance for static instantiation. Dynamic Instantiation of an Object struct my_object * pMyObj; ... pMyObj = (struct my_object *) malloc (sizeof (struct my_object)); if (pMyObj != NULL) { objectInit (pMyOjb); return (OK); } else { /* failure path */ return (ERROR); } Static Instantiation of an Object struct my_object myObj; ... objectInit (&myOjb); /* myObj now ready for use */ Static instantiation of objects has the following advantages: ■ The application logic is made simpler by not having to consider the case when dynamic allocation fails. ■ Compile time declaration of objects does not take up space in the executable file or flash memory. If an object is merely declared at compile time but not initialized, it is placed by the compiler in the un-initialized data section (also known as the bss section). Un-initialized data is required by the ANSI C standard to be of value zero. Hence the un-initialized data section (the bss section) of a program does not occupy any space in an executable file or in VxWorks ROM images. Un-initialized data does contribute to the programs run-time footprint in memory, but so does dynamic allocation. The program will not consume any more memory footprint than it did with dynamic allocation of objects. Using static instantiation whenever possible is more robust, deterministic and fast. Static instantiation of objects is therefore much better suited for real-time applications. On the other hand some applications are inherently dynamic in nature. For these, dynamic creation and deletion is always available. 57 2 VxWorks Kernel Programmer's Guide, 6.6 Static Instantiation of Objects Kernel objects such as tasks, semaphores, message queues and watchdogs can be instantiated statically using the same principles outlined above. Normally these objects are created using the appropriate create routines for that type of object, and deleted using the appropriate delete routine. As mentioned before, creation and deletion involve dynamic memory allocation and free respectively. Static instantiation of objects is a two-step process. First the object to be created is declared, usually at global scope. Next the declared object is initialized using an initialization routine, which makes it ready for use. In contrast, dynamic creation with create routines is a one-step process. Static instantiation of objects is thus a little less convenient, but more deterministic. Users can choose the style that suits their purpose. NOTE: Static instantiation should only be used for objects that are kernel-resident. It is not meant to be used to create objects in a process (RTP). The following sections describe an alternative static instantiation method for each of these entities. Scope Of Static Declarations The macros declaring kernel objects (that is VX_BINARY_SEMAPHORE, VX_TASK, and so on) are usually declared as global variables. Since all these kernel objects are used for inter-task communication and synchronization, their IDs are the means by which other tasks use these objects. Hence global objects and global IDs are the common method by which these objects are accessed and used. However it is not always necessary that they be global. An object declaration can also be done at function scope provided the object stays in a valid scope for the duration of its use. Static Instantiation of Tasks The taskSpawn( ) routine has been the standard method for instantiating tasks. This API relies on dynamic allocations. In order to instantiate tasks statically several macros have been provided to emulate the dynamic instantiation capability provided by taskSpawn( ) and related routines. The VX_TASK macro declares a task object at compilation time. It takes two arguments: the task name and its stack size. When calling taskSpawn( ) the name may be a NULL pointer, but when using the VX_TASK macro, a name is 58 2 Kernel 2.6 Kernel Applications mandatory. The stack size must evaluate to a non-zero integer value and must be a compile-time constant. The VX_TASK_INSTANTIATE macro is the static equivalent of the taskSpawn( ) routine. It initializes and schedules the task, making it run according to its priority. VX_TASK_INSTANTIATE evaluates to the task ID of the spawned task if it was successful, or ERROR if not. The following example illustrate spawning tasks statically: #include #include VX_TASK(myTask,4096); int myTaskId; STATUS initializeFunction (void) { myTaskId = VX_TASK_INSTANTIATE(myTask, 100, 0, 4096, pEntry, \ 0,1,2,3,4,5,6,7,8,9); if (myTaskId != ERROR) return (OK); else return (ERROR); } /* instantiation succeeded */ Sometimes users may prefer to initialize a task, but keep it suspended until needed later. This can be achieved by using the VX_TASK_INITIALIZE macro, as illustrated below. Since the task is left suspended, users are responsible for calling taskActivate( ) in order to run the task. #include #include VX_TASK(myTask,4096); int myTaskId; STATUS initializeFunction (void) { myTaskId = VX_TASK_INITIALIZE(myTask, 100, 0, 4096, pEntry, \ 0,1,2,3,4,5,6,7,8,9); if (myTaskId != NULL) { taskActivate (myTaskId); return (OK); } else return (ERROR); } 59 2 VxWorks Kernel Programmer's Guide, 6.6 It is the programmer’s responsibility to pass the same name to VX_TASK_INSTANTIATE as was used in the VX_TASK declaration, which is myTask in this case. The arguments to VX_TASK_INSTANTIATE and their meaning are the same as those passed to taskSpawn( ). This makes the usage of VX_TASK_INSTANTIATE consistent with taskSpawn( ). Please note the backslash that continues the argument list on the succeeding line. This backslash character is crucial if the arguments span more than one line. This is to ensure correct macro expansion. For more information, see the API reference for taskLib. Static Instantiation Of Semaphores The macros VX_BINARY_SEMAPHORE, VX_COUNTING_SEMAPHORE and VX_MUTEX_SEMAPHORE are used to declare a semaphore of type binary, counting, and mutex respectively. These macros take the semaphore name as an argument. The declared semaphores are initialized by calling routines semBInitialize( ), semCInitialize( ) and semMInitialize( ) respectively. The three semXInitialize( ) routines are the equivalents of their respective semXCreate( ) routines, the only difference being that the semaphore same name used in the associated VX_XXX_SEMAPHORE be passed to the semXInitialize( ) routines. The return value from the semXInitialize( ) routines is a semaphore ID that is then used to perform all operations on the semaphores. The following example illustrates static instantiation of a binary semaphore: #include #include VX_BINARY_SEMAPHORE(mySemB); SEM_ID mySemBId; /* declare the semaphore */ /* semaphore ID for further operations */ STATUS initializeFunction (void) { if ((mySemBId = semBInitialize (mysemB, options, 0)) == NULL) return (ERROR); /* initialization failed */ else return (OK); } For more information, see the API reference for semLib. Static Instantiation of Message Queues The macro VX_MSG_Q is used to declare a message queue at compile time. It takes three parameters: the name, the maximum number of messages in the message queue, and the maximum size of each message. 60 2 Kernel 2.6 Kernel Applications After this declaration, the msgQInitialize( ) routine is used to initialize the message queue and make it ready for use. The following example illustrates static instantiation of a message queue: #include #include VX_MSG_Q(myMsgQ,100,16); MSG_Q_ID myMsgQId; /* declare the msgQ */ /* MsgQ ID to send/receive messages */ STATUS initializeFunction (void) { if ((myMsgQId = msgQInitialize (myMsgQ, 100, 16, options)) == NULL) return (ERROR); /* initialization failed */ else return (OK); } As with other static instantiation macros it is crucial to pass exactly the same name used in the VX_MSG_Q declaration to the msgQInitialize( ) routine, or else compilation errors will result. Also it is crucial to pass exactly the same values for the message size and maximum number of messages as was passed to the VX_MSG_Q macro. For more information, see the API reference for msgQLib. Static Instantiation of Watchdogs The macro VX_WDOG is used to declare a watchdog at compile time. It takes one parameter, the name of the watchdog. After this declaration, the routine wdInitialize( ) is used to initialize the watchdog and make it ready for use. #include #include VX_WDOG(myWdog); WDOG_ID myWdogId; /* declare the watchdog */ /* watchdog ID for further operations */ STATUS initializeFunction (void) { if ((myWdogId = wdInitialize (myWdog)) == NULL) return (ERROR); /* initialization failed */ else return (OK); } As with other static instantiation macros it is crucial to pass exactly the same name used in the VX_WDOG declaration to the wdInitialize( ) routine, or else compilation errors will result. For more information, see the API reference for wdLib. 61 2 VxWorks Kernel Programmer's Guide, 6.6 2.6.5 Applications and VxWorks Kernel Component Requirements VxWorks is a highly configurable operating system. When kernel application modules are built independently of the operating system (see 2.6.6 Building Kernel Application Modules, p.62), the build process cannot determine if the instance of VxWorks on which the application will eventually run has been configured with all of the components that the application requires (for example, networking and file systems). It is, therefore, useful for application code to check for errors indicating that kernel facilities are not available (that is, check the return values of API calls) and to respond appropriately. When kernel application modules are linked with the operating system, the build system generates errors with regard to missing components. Both Workbench and the vxprj command-line tool also provide a mechanisms for checking dependencies and for reconfiguring VxWorks accordingly. 2.6.6 Building Kernel Application Modules The VxWorks environment provides simple mechanisms for building kernel application modules, including a useful set of default makefile rules. Both the IDE and command line can be used to build applications. For command-line use, the wrenv utility program can be used to open a command shell with the appropriate host environment variables set. See VxWorks Command-Line Tools User's Guide: Creating a Development Shell with wrenv and the VxWorks Command-Line Tools User’s Guide. Using Makefile Include Files for Kernel Application Modules You can make use of the VxWorks makefile structure to put together your own application makefiles quickly and efficiently. If you build your application directly in a BSP directory (or in a copy of one), you can use the makefile in that BSP, by specifying variable definitions that include the components of your application. You can specify values for these variables either from the make command line, or from your own makefiles (when you take advantage of the predefined VxWorks make include files). ADDED_CFLAGS Application-specific compiler options for C programs. ADDED_C++FLAGS Application-specific compiler options for C++ programs. 62 2 Kernel 2.6 Kernel Applications Additional variables can be used to link kernel application modules with the VxWorks image; see 2.6.8 Linking Kernel Application Object Modules with VxWorks, p.64. For more information about makefiles, see the VxWorks Command-Line Tools User’s Guide. You can also take advantage of the makefile structure if you develop kernel application modules in separate directories. Example 2-1 illustrates the general scheme. Include the makefile headers that specify variables, and list the object modules you want built as dependencies of a target. This simple scheme is usually sufficient, because the makefile variables are carefully designed to fit into the default rules that make knows about.2 Example 2-1 Skeleton Makefile for Kernel Applications # # # # # # Makefile - makefile for ... Copyright ... DESCRIPTION This file specifies how to build ... ## It is often convenient to override the following with "make CPU=..." CPU = cputype TOOL = diab include $(WIND_BASE)/target/h/make/defs.bsp ## Only redefine make definitions below this point, or your definitions ## will be overwritten by the makefile stubs above. exe : myApp.o For information about build options, see the VxWorks Architecture Supplement for the target architecture in question. For information about using makefiles to build applications, see the VxWorks Command-Line Tools User’s Guide. Statically Linking Kernel Application Modules In general, kernel application modules do not need to be linked before being downloaded to the target. However, when several modules cross reference each other they should be linked to form a single module. With C++ code, this linking should be done before the munch step. (See 13.5.2 Munching a C++ Application Module, p.650.) 2. However, if you are working with C++, it may be also convenient to copy the .cpp.out rule from installDir/vxworks-6.x/target/h/make/rules.bsp into your application’s makefile. 63 2 VxWorks Kernel Programmer's Guide, 6.6 The following example is a command to link several modules, using the Wind River linker for the PowerPC family of processors: c:\> dld -o applic.o -r applic1.o applic2.o applic3.o Similarly, this example uses the GNU linker: c:\> ldppc -o applic.o -r applic1.o applic2.o applic3.o In either case, the command creates the object module applic.o from the object modules applic1.o, applic2.o, and applic3.o. The -r option is required, because the object-module output must be left in relocatable form so that it can be downloaded and linked to the target VxWorks image. Any VxWorks facilities called by the kernel application modules are reported by the linker as unresolved externals. These are resolved by the loader when the module is loaded into VxWorks memory. ! WARNING: Do not link each kernel application module with the VxWorks libraries. Doing this defeats the load-time linking feature of the loader, and wastes space by writing multiple copies of VxWorks system modules on the target. 2.6.7 Downloading Kernel Application Object Modules to a Target Kernel application object modules can be downloaded from Workbench or from the kernel shell. Once a module has been loaded into target memory, any subroutine in the module can be invoked, tasks can be spawned, debugging facilities employed with the modules, and so on. It is often useful to make use of a startup routine to run the application (see 2.6.2 Application Structure, p.52). For information about using the kernel shell and module loader, see 12.2 Kernel Shell, p.577 and 12.3 Kernel Object-Module Loader, p.603. For information about using theWorkbench, see the Wind River Workbench User’s Guide. 2.6.8 Linking Kernel Application Object Modules with VxWorks In order to produce complete systems that include kernel application modules, the modules must be statically linked with the VxWorks image. The makefile EXTRA_MODULES variable can be used to do so. It can be used from the command line as follows: % make EXTRA_MODULES="foo.o" 64 2 Kernel 2.6 Kernel Applications For more information about using makefile variables, see 2.6.6 Building Kernel Application Modules, p.62. To include your kernel application modules in the system image using a makefile, identify the names of the application object modules (with the .o suffix) with EXTRA_MODULES. For example, to link the module myMod.o with the operating system, add a line like the following: EXTRA_MODULES = myMod.o Building the system image with the module linked in is the final part of this step. In the project directory, execute the following command: c:\myVxProj\osProj> make vxWorks For information about how to have kernel applications start automatically at boot time, see 2.6.10 Configuring VxWorks to Run Applications Automatically, p.66. 2.6.9 Image Size Considerations The size of the system image is often an important consideration, particularly when kernel application modules are linked with the operating system. This is true whether the image is loaded by a boot loader or is self-booting (see 2.4.1 VxWorks Image Types, p.15). ! CAUTION: For ROM-based images, ensure that ROM_SIZE configuration parameter reflects the capacity of the ROMs used. Boot Loader and Downloadable Image Generally, VxWorks boot loader code is copied to a start address in RAM above the constant RAM_HIGH_ADRS, and the boot loader in turn copies the downloaded system image starting at RAM_LOW_ADRS. The values of these constants are architecture dependent, but in any case the system image must not exceed the space between the two. Otherwise the system image will overwrite the boot loader code while downloading, potentially killing the booting process. To help avoid this, the last command executed when you build a new VxWorks image is vxsize, which shows the size of the new executable image and how much space (if any) is left in the area below the space used for boot ROM code: vxsize 386 -v 00100000 00020000 vxWorks vxWorks: 612328(t) + 69456(d) + 34736(b) = 716520 (235720 bytes left) (In this output, t stands for text segment, d for data segment, and b for bss.) 65 2 VxWorks Kernel Programmer's Guide, 6.6 Make sure that RAM_HIGH_ADRS is less than LOCAL_MEM_SIZE. If your new image is too large, vxsize issues a warning. In this case, you can reconfigure the boot loader to copy the boot ROM code to a sufficiently high memory address by increasing the value of RAM_HIGH_ADRS in config.h and in the BSP’s makefile (both values must agree). Then rebuild the boot loader. For more information, see Persistent Memory Region, p.150. Self-Booting Image For self-booting images, the data segment of a ROM-resident VxWorks system is loaded at RAM_LOW_ADRS (defined in the makefile) to minimize fragmentation. For a CPU board with limited memory (under 1 MB of RAM), make sure that RAM_HIGH_ADRS is less than LOCAL_MEM_SIZE by a margin sufficient to accommodate the data segment. Note that RAM_HIGH_ADRS is defined in both the BSP makefile and config.h (both values must agree). 2.6.10 Configuring VxWorks to Run Applications Automatically VxWorks can be configured to start kernel applications automatically at boot time. To do so, perform the following steps: 1. Configure VxWorks with the INCLUDE_USER_APPL component. 2. Add a call to the application’s entry-point routine in the usrAppInit( ) routine stub, which is in installDir/vxworks-6.x/target/proj/projDir/usrAppInit.c. Assuming, for example, that the application entry point routine myAppStartUp( ) starts all the required application tasks, you would add a call to that routine in the usrAppInit( ) stub as follows: void usrAppInit (void) { #ifdef USER_APPL_INIT USER_APPL_INIT; #endif /* for backwards compatibility */ myAppStartUp(); } 3. 66 Link the kernel-base application object modules with the kernel image (see 2.6.8 Linking Kernel Application Object Modules with VxWorks, p.64). 2 Kernel 2.7 Custom Kernel Libraries 2.7 Custom Kernel Libraries For information about creating custom kernel libraries, see the VxWorks Command-Line Tools User’s Guide. 2.8 Custom VxWorks Components and CDFs A VxWorks component is the basic unit of functionality with which VxWorks can be configured. VxWorks kernel components are described in Component Description Files (CDFs), using the Component Description Language (CDL). (For introductory information about the components provided with VxWorks, see 2.4.2 VxWorks Components, p.17.) Wind River recommends using CDFs for developing extensions to the VxWorks operating system. If you wish to develop components that make APIs available to RTP applications (which run in user mode as real-time processes), also see 2.9 Custom System Calls, p.100. NOTE: Functionality can be added to VxWorks in the form of kernel modules that do not have to be defined as VxWorks components (see 2.6 Kernel Applications, p.51). However, in order to make use of either Workbench or the vxprj command-line configuration facilities, to define dependencies between components, and so on, extensions to the operating system should be developed using CDFs. A CDF identifies the binary and source code elements that make up the component, its configuration parameters, relationship to other components, and so on. CDFs also define information about how components are displayed in the Workbench kernel configuration facility, and they can be used to group components into predefined sets to facilitate VxWorks configuration. While some components are autonomous, some have dependencies on other components, which must be included in the configuration of the operating system for run-time operation. Both Workbench and the vxprj command-line facility use CDFs for configuring the operating system with selected components, for setting component parameter values, and so on. Workbench also uses information in CDFs to display the names and descriptions of components, and to provide links to online help. For 67 2 VxWorks Kernel Programmer's Guide, 6.6 information about Workbench and the command-line facilities used for configuring and building VxWorks, see the Wind River Workbench User’s Guide and the VxWorks Command-Line Tools User’s Guide. The first of the sections that follow provide procedural instructions for creating, installing, and testing a CDF; then additional sections provide reference information about CDL and its constituent elements. 2.8.1 Creating and Modifying Components This section provides an instructional example of how to create a component or to modify an existing one. The example is generally useful in its illustration of the process, but does not make exhaustive use of CDL objects and properties. You must follow the CDL conventions when creating a CDF. For detailed information, see the sections referenced below in the instructions, as well as 2.8.13 CDF Template, p.96. After creating a CDF, you must place the file in the proper path to ensure that the configuration facility reads the information and includes the component in the hierarchy of components. For information in this regard, see 2.8.2 CDF Precedence and CDF Installation, p.75 and Adding New CDFs to the VxWorks Installation Tree, p.77. Information about testing a component is provided in 2.8.3 Testing New Components, p.78. Defining a Component This section describes the process of defining your own component. To allow for the greatest flexibility, there is no convention governing the order in which properties describe a component or the sequence in which CDL objects are entered into a component description file. The following steps taken to create the component INCLUDE_FOO are a suggested order only; the sequence is not mandatory. Nor is there meant to be any suggestion that you use all of the properties and object classes described. The naming conventions for CDL are described in 2.8.5 CDF Naming Conventions, p.80. Note that CDF files must have a .cdf suffix. 68 2 Kernel 2.8 Custom VxWorks Components and CDFs Step 1: Name and Provide a Synopsis To create your new component, first name it and provide a synopsis of its utility. Component NAME SYNOPSIS ... INCLUDE_FOO { foo component this is just an example component In the component INCLUDE_FOO, the NAME property is foo component. The SYNOPSIS property instructively informs the user that this is just an example component. NAME and SYNOPSIS properties affect user presentation only; they have no bearing on initialization sequence or dependencies. For information about the properties of the component object (NAME and so on), see 2.8.6 Component CDF Object, p.81. Step 2: Describe the Code-Related Elements Next, describe your component’s code portions by defining any modules and source configlettes that should be configured in during the build. If the component INCLUDE_FOO has an object module associated with it—and not source code—use the MODULES property to specify it. You can specify any number of modules this way. In the following example, fooLib.o and fooShow.o are listed: ... MODULES HDR_FILES ARCHIVE CONFIGLETTES ... fooLib.o fooShow.o foo.h fooLib.a fooConfig.c The configuration facilities (Workbench and vxprj) automatically analyze object module dependencies in order to calculate component dependencies. (Workbench also offers visibility into component dependencies by graphically presenting component relationships.) For example, if fooLib.o has an unresolved global for logMsg( ), an automatic dependency upon the component INCLUDE_LOGGING is detected. For components not shipped in object module format, CDL supports the explicit listing of component dependencies. If the source portion contains a call to logMsg( ), the configuration facility does not detect the dependency; instead, an explicit dependency upon INCLUDE_LOGGING should be declared using the REQUIRES property. See Step 6. 69 2 VxWorks Kernel Programmer's Guide, 6.6 If your module is not located in the standard path, use the ARCHIVE property to specify the archive name, for example, /somePath/fooLib.a. (For additional instructions concerning the use of ARCHIVE, see Step 10.) NOTE: Developers should create their own archives for custom components. Do not modify Wind River archives. Use the HDR_FILES property to specify any .h files associated with the component, like foo.h. These files are emitted in prjConfig.c, providing the initialization routine with a declaration. If there is source code that should be compiled as part of the component, put it in a .c file and specify the file name in the CONFIGLETTES property, for example, fooConfig.c. Component parameters should be referenced in the configlette or in the initialization routine; otherwise they have no effect. For detailed information about the properties of the component object (MODULES and so on), see 2.8.6 Component CDF Object, p.81. Step 3: Set Up Initialization If the component must be initialized, use the INIT_RTN property of the component object class to specify the initialization routine and its arguments to be called, as in fooInit(arg1, arg2). If your component needs more than a single line of initialization, create or add the initialization code to a .c file and use the CONFIGLETTES property instead. By associating a configlette with an initialization routine, you are securing the configlette’s place in the initialization sequence. ... INIT_RTN ... fooInit(arg1, arg2); If you are not using the MODULES property of the component object, use the LINK_SYMS property to include your object module from a linked archive. The system generates an unresolved reference to the symbol (fooRtn1 in this example), causing the linker to resolve it by extracting your module from the archive. ... LINK_SYMS ... fooRtn1 For more information about the INIT_RTN property of the component object, see and 2.8.6 Component CDF Object, p.81. 70 2 Kernel 2.8 Custom VxWorks Components and CDFs Step 4: Establish the Initialization Sequence Initialization order is important. You can control when in the initialization sequence your component is initialized with the _INIT_ORDER property. A component (or initialization group) that is bound to an existing initialization group using the _INIT_ORDER property is, by default, initialized last within that group. This is typically the desired effect; however, you can override this behavior by explicitly using the INIT_BEFORE property. ... _INIT_ORDER INIT_BEFORE ... usrRoot INCLUDE_USER_APPL In the example, INCLUDE_FOO is declared a member of the usrRoot initialization group. INIT_BEFORE has been used for fine control, and INCLUDE_FOO is initialized before INCLUDE_USER_APPL. For more information about the _INIT_ORDER and INIT_BEFORE properties of the component object, see and 2.8.6 Component CDF Object, p.81. Alternatively, you can create a new initialization group and declare INCLUDE_FOO a member; however, you would have to declare the new initialization group a member of an existing initialization group. For information on initialization groups, see 2.8.8 Initialization Group CDF Object, p.88. NOTE: INIT_BEFORE only affects ordering within the initialization group. Do not reference a component that is not in the initialization group; this has no effect. NOTE: The INIT_AFTER property has no effect in this release. Step 5: Link Helpful Documentation Specify related reference entries (in HTML format) with the HELP property. ... HELP ... fooMan By default, a build automatically includes reference entries related to values declared by the MODULES and INIT_RTN properties. In the case of INCLUDE_FOO, in addition to fooMan.html, which is specified by HELP, the build associates the fooLib and fooShow libraries and the fooInit( ) routine. For more information about the HELP property of the component object, see and 2.8.6 Component CDF Object, p.81. 71 2 VxWorks Kernel Programmer's Guide, 6.6 Step 6: Define Dependencies Use the REQUIRES and INCLUDE_WHEN properties to explicitly declare dependencies among components. (See Step 2 to learn how the configuration facility automatically configures object module-related dependencies.) The configuration facility does not detect implicit dependencies when a component is not shipped in object module format. Likewise, no dependencies are detected when symbols are referenced by pointers at run-time. Both circumstances require you to declare dependencies explicitly. ... REQUIRES INCLUDE_WHEN ... INCLUDE_LOGGING INCLUDE_POSIX_AIO INCLUDE_POSIX_MQ In the example, REQUIRES declares that INCLUDE_LOGGING must be configured along with INCLUDE_FOO. INCLUDE_WHEN tells the system that whenever the components INCLUDE_POSIX_AIO and INCLUDE_POSIX_MQ are included, then INCLUDE_FOO must also be included. For information about properties of the component object (including REQUIRES and so on), see 2.8.6 Component CDF Object, p.81. NOTE: In general, the configuration facility is designed to increase flexibility when selecting components, that is, to increase scalability; specifying a REQUIRES relationship reduces flexibility. Be sure that using REQUIRES is the best course of action in your situation before implementing it. Step 7: List Associated Parameters In the component object, use the CFG_PARAMS property to declare all associated parameters, for example, FOO_MAX_COUNT. ... CFG_PARAMS ... FOO_MAX_COUNT For information about properties of the component object (including CFG_PARAMS), see 2.8.6 Component CDF Object, p.81. Step 8: Define Parameters For each parameter declared by CFG_PARAMS, create a parameter object to describe it. Provide a name using the NAME property. Use the TYPE property to specify the data type, either int, uint, bool, string, exists, or untyped. 72 2 Kernel 2.8 Custom VxWorks Components and CDFs Use the DEFAULT property to specify a default value for each parameter. Parameter NAME TYPE DEFAULT } FOO_MAX_COUNT Foo maximum uint 50 { 2 For information about the parameter object and its properties, see 2.8.7 Parameter CDF Object, p.87. ! CAUTION: A component is considered mis-configured if it contains a parameter without an assigned value. Be sure to assign default values, unless there is no reasonable default and you want to force the user to set it explicitly. (Other CDF files with higher precedence, may of course be used to set the parameter value; see CDF File Naming and Precedence, p.75.) Step 9: Define Group Membership A component must be associated with either a folder or selection, otherwise it is not visible in Workbench. Assign a component to a folder because of its logical inclusion in the group defined by the folder, based on similar or shared functionality, for example. By including a component in a folder, you make it possible for the user to load it simultaneously with other components in its group by declaring them as default values for the folder, using the folder object’s DEFAULTS property. ... _CHILDREN ... FOLDER_ROOT The _CHILDREN property declares that INCLUDE_FOO is a child component of folder FOLDER_ROOT. The prepended underscore (“_”) serves to reverse the relationship declared by the property CHILDREN, which means that _CHILDREN identifies the parent. You can also use _DEFAULTS in conjunction with _CHILDREN to specify a component as a default component of a folder. If you think a component is becoming too complex, you can divide it into a set of components assigned to a folder or selection object. In the following example, INCLUDE_FOO has been specified as part of a selection. You can add or remove the group from your configuration as a unit rather than by its individual components. For folders, the DEFAULTS property specifies the base set of components that are included if the group is configured without any overrides. For selections, the DEFAULTS property specifies the components that are included to satisfy the count (declared by the COUNT property), if you provide no alternative values. 73 VxWorks Kernel Programmer's Guide, 6.6 In a selection group, the COUNT property specifies the minimum and maximum number of included components. If the user exceeds these limits the system flags the selection as mis-configured. Selection NAME SYNOPSIS COUNT CHILDREN DEFAULTS SELECT_FOO { Foo type Select the type of desired FOO support 0-1 INCLUDE_FOO_TYPE1 \ INCLUDE_FOO_TYPE2 \ INCLUDE_FOO_TYPE3 INCLUDE_FOO_TYPE1 } For information about the folder and section objects and its properties, see 2.8.11 Folder CDF Object, p.92 and 2.8.12 Selection CDF Object, p.94. Step 10: Create a Dummy Component The configuration facility analyzes archives only when they are associated with included components. This creates a chicken and egg problem: in order to know about a particular archive, the configuration facility would need to analyze components before they are actually added. In other words, if you add a component declared with an ARCHIVE property, the configuration analysis is done without knowing what the value of ARCHIVE is. So, if your component includes an archive with several object modules, you should create a dummy component that is always included, making it possible for the configuration facility to know that a new archive should be read. Call such a component INSTALL_FOO. It should contain only NAME, SYNOPSIS, and ARCHIVE properties. The user cannot add other components from the same archive until INSTALL_FOO is added. For information about properties of the component object (including ARCHIVE), see 2.8.6 Component CDF Object, p.81. ! CAUTION: Do not alter Wind River-supplied CDFs directly. Use the naming convention to create a file whose higher precedence overrides the default properties of Wind River-supplied components. Modifying a Component Do not modify any Wind River CDF. However, you can effectively modify the properties of existing components by re-specifying them in another, higher priority CDF file. Third-party CDF files are 74 2 Kernel 2.8 Custom VxWorks Components and CDFs by convention read last and therefore have the highest priority. Use the naming convention to create a high-precedence CDF file that overrides the default properties of Wind River components. For detailed information, see 2.8.2 CDF Precedence and CDF Installation, p.75. In the following example, the default number of open file descriptors (NUM_FILES) in the standard Wind River component INCLUDE_IO_SYSTEM has been modified. The normal default value is 50. Parameter NUM_FILES { DEFAULT 75 } By adding these example lines of code to a third-party CDF file, by removing and adding the component if it is already in the configuration, and by re-building the project, the value of NUM_FILES is changed to 75. The original Wind River CDF file, 00vxWorks.cdf, is not changed; the default property value is changed because the third-party file has higher precedence. Other property values remain the same unless specifically redefined. ! CAUTION: Do not alter the Wind River-supplied source configlette files in installDir/vxworks-6.x/target/config/comps/src. ! CAUTION: Do not alter Wind River-supplied CDFs directly. Use the naming convention to create a file whose higher precedence overrides the default properties of Wind River-supplied components. 2.8.2 CDF Precedence and CDF Installation More than one CDF may define a given component and its properties. The precedence of multiple definitions is determined by a numbering scheme used with the CDF naming convention and by the order in which directories containing CDFs are read by the configuration facility. CDF File Naming and Precedence Wind River reserves the first 50 numbers, that is 00fileName.cdf through 49fileName.cdf. The remaining numbers, 50 through 99, may be used by third parties for their components. Higher number files have greater precedence than lower number files (when the remainder of the name is the same); for example, the definition of the INCLUDE_FOO component in 66comp_foo.cdf override those in 55comp_foo.cdf. 75 2 VxWorks Kernel Programmer's Guide, 6.6 This method of setting precedence allows project, BSP, and CPU architecture-specific overrides of generic components or parameters. For example, if a BSP provider wanted to change the maximum number of files that can be open (NUM_FILES) to 75 from the default value of 50, it can be done in a BSP-specific CDF file with a higher file number that has the following entry in it: Parameter NUM_FILES { DEFAULT 75 } CDF Directories and Precedence The component description files are read at two points by the configuration facility: ■ When a project is created. ■ After component description files are changed and the project build occurs. The order in which CDFs are read is significant. If more than one file describes the same property of the same component, the one read last overrides all earlier ones. The intent is to allow component description files to have some precedence level. Files read later have higher precedence than those read earlier. Precedence is established in two complementary ways: ■ CDF files reside in certain directories, and those directories are read in a specified order. ■ Within one of these directories, CDFs are read in alphanumeric order. The configuration facility sources all .cdf files in any of the following directories. These directories are read in the order in which they are presented: 1. installDir/vxworks-6.x/target/config/comps/vxWorks Contains all generic VxWorks components. 2. installDir/vxworks-6.x/target/config/comps/vxWorks/arch/arch Contains all architecture-specific VxWorks components (or component overrides). 3. installDir/vxworks-6.x/target/config/bspName Contains all BSP-specific components. 4. the project directory Contains all other components. 76 2 Kernel 2.8 Custom VxWorks Components and CDFs Within a directory, to control alphanumeric order, a two digit number is prepended to each .cdf file to determine the order of precedence within a given directory. See 2.8.5 CDF Naming Conventions, p.80. Elements of Components in a VxWorks Installation Tree Wind River delivers the parts of its components in the following locations: ■ Source code modules are usually found in the installDir/vxworks-6.x/target/src or target/config directories. ■ Headers are found in installDir/vxworks-6.x/target/h; object modules are delivered in installDir/vxworks-6.x/target/lib/objARCH. ■ Component description files are in installDir/vxworks-6.x/target/config/comps/vxWorks. ■ Component configlettes (source fragments) are in installDir/vxworks-6.x/target/config/comps/src. Third parties are not limited to this arrangement, and the location of component elements can be fully described in the component description file. Adding New CDFs to the VxWorks Installation Tree If you have created a new CDF, you must place it in the appropriate path, based on the nature of the contents and the desired level of precedence. Your choices of paths (as described in CDF Directories and Precedence, p.76) are as follows: ■ installDir/vxworks-6.x/target/config/comps/vxWorks for generic VxWorks component descriptions only ■ installDir/vxworks-6.x/target/config/comps/vxWorks/arch/arch for architecture-specific VxWorks component descriptions ■ installDir/vxworks-6.x/target/config/config/bspName for board-specific component descriptions ■ the project directory for all other files Wind River recommends that third parties place their component source code and object elements in a directory, such as installDir/vxworks-6.x/target/config/vendorName. The location of the component description file (CDF) depends on where in the system the components should be integrated. To be able to integrate a new general-purpose VxWorks component into the system, the CDF must be located in 77 2 VxWorks Kernel Programmer's Guide, 6.6 installDir/vxworks-6.x/target/config/comps/vxWorks. If it is a BSP-specific component, the file should be located in the BSP directory. If it is specific to a single project, it should be located in the project directory (installDir/vxworks-6.x/target/proj/projectName). Be sure to follow the proper naming and numbering conventions, which are described in 2.8.5 CDF Naming Conventions, p.80. 2.8.3 Testing New Components There are several tests that can run to verify that components have been written correctly: ■ Check Syntax and Semantics This vxprj command provides the most basic test: vxprj component check [projectFile] [component ... ] For example: % vxprj component check MyProject.wpj If no project file is specified, vxprj looks for a .wpj file in the current directory. If no component is specified, vxprj checks every component in the project. This command invokes the cmpTest routine, which tests for syntactical and semantic errors Based on test output, make any required modifications. Keep running the script until you have removed the errors. ■ Check Component Dependencies You can test for scalability bugs in your component by running a second vxprj command, which has the following syntax: vxprj component dependencies [projectFile] component [component ... ] For example, the following command displays a list of components required by INCLUDE_OBJ_LIB, as well as those that require the component: % vxprj component dependencies INCLUDE_OBJ_LIB If no project file is specified, vxprj looks for a .wpj file in the current directory. ■ Check the Component Hierarchy in Workbench Verify that selections, folders, and new components you have added are properly included by making a visual check of the Workbench component hierarchy. 78 2 Kernel 2.8 Custom VxWorks Components and CDFs Look at how your new elements appear in the folder tree. Check the parameters associated with a component and their parameter default values. If you have added a folder containing components, and have included that folder in your configuration, the Workbench component hierarchy should display in boldface all components listed as defaults for that folder (that is, values for the DEFAULTS property). ■ Build and Boot the System Verify that the resulting image builds and boots. 2.8.4 Component Description Language The component description language (CDL) is used in component description files (CDFs) to describe software components. Each CDF has the suffix .cdf. A single file can define more than one component. The Component Descriptor Language has several classes of objects, each of which has various properties. Three of the object classes are used to define a software component, its configuration options, and its initialization routine. These objects are discussed in the following sections: ■ 2.8.6 Component CDF Object, p.81 ■ 2.8.7 Parameter CDF Object, p.87 ■ 2.8.8 Initialization Group CDF Object, p.88 Two classes of objects are used to group components into a single unit for ease of configuration. It is described in the following section: ■ 2.8.9 Bundle CDF Object, p.90 ■ 2.8.10 Profile CDF Object, p.91 Two additional classes of objects are used to control the display of components in the Workbench kernel configuration facility. They are described in the following sections: ■ 2.8.11 Folder CDF Object, p.92 ■ 2.8.12 Selection CDF Object, p.94 For information about naming conventions, see 2.8.5 CDF Naming Conventions, p.80. 79 2 VxWorks Kernel Programmer's Guide, 6.6 Based on the operating system components selected by the user, the configuration facilities (Workbench or vxprj) create the system configuration files prjComps.h, prjParams.h, and prjConfig.c, which are used in building the specified system. For information about how the configuration and code generation facilities work, see the Wind River Workbench User’s Guide and the VxWorks Command-Line Tools User’s Guide. 2.8.5 CDF Naming Conventions Follow these conventions when creating CDFs, where FOO (or Foo) is the variable element of the naming convention: ■ All bundles names are of the form BUNDLE_FOO. ■ All component names are of the form INCLUDE_FOO. ■ All VxBus driver component names are of the form INCLUDE_driverType_driverName (for example, DRV_SIO_NS16550). ■ All folders names are of the form FOLDER_FOO. ■ All selection names are of the form SELECT_FOO. ■ Parameter names should not match the format of any other object type, but are otherwise unrestricted. For example, you can use FOO_XXX, but not INCLUDE_FOO. ■ All initialization group names should be of the form initFoo. However, Wind River initialization groups use the form usrFoo for backwards compatibility reasons. ■ All component description files have a .cdf suffix. ■ All .cdf file names begin with two decimal digits; for example, 00comp_foo.cdf. These first two digits control the order in which .cdf files are read within a directory. See 2.8.2 CDF Precedence and CDF Installation, p.75 for more information. Note that more than one component can be defined in a single CDF. New component description files should be independent of existing files, with two exceptions: ■ 80 New component objects should be bound into an existing folder or selection for GUI display purposes. 2 Kernel 2.8 Custom VxWorks Components and CDFs ■ New component object initialization routines must be associated with an existing initialization group. A new component object can be bound to an existing folder or selection, and to an existing initialization group, without modifying the existing elements. By prepending an underscore (“_”) to certain component properties, you can reverse the meaning of the property. For example, if there is already a folder FOLDER_EXISTING and an initialization group initExisting, you can bind a new component (which is defined in a different file) to it as follows: Component INCLUDE_FOO ... _CHILDREN FOLDER_EXISTING _INIT_ORDER initExisting } The property _CHILDREN has the opposite relationship to FOLDER_EXISTING as CHILDREN; that is, _CHILDREN identifies the parent. In other words, it produces the same effect as FOLDER_EXISTING having the component INCLUDE_FOO on its list of children—without any modifications being made to the CDF containing the FOLDER_EXISTING object. Note that INIT_BEFORE can be used _INIT_ORDER to define exactly where in the initialization group the component should be placed. 2.8.6 Component CDF Object Components are the basic units of configurable software. They are the smallest, scalable unit in a system. With either Workbench or the command-line vxprj facility, a user can reconfigure VxWorks by including or excluding a component, as well as modifying some of its characteristics. The properties of a component include: ■ Identification of the object code (modules) and source code (configlettes) used in the build of a project. ■ Identification of configuration parameters, which are typically preprocessor macros used within a component’s configuration code. ■ Integration information that controls how a component is integrated into an executable system image (for example, an initialization routine). For information about how to group components in to a bundle of components, see 2.8.9 Bundle CDF Object, p.90. 81 2 VxWorks Kernel Programmer's Guide, 6.6 For information about displaying information about components in the Workbench kernel configuration facility, see 2.8.11 Folder CDF Object, p.92 and 2.8.12 Selection CDF Object, p.94. Component Properties The component object class defines the source and object code associated with a component, much of the integration information, and any associated parameters. Dependencies among components can be detected and the related components can be automatically added by the configuration facility (GUI or CLI). It does so by analyzing the global symbols in each object module that belongs to the component, and then determining which other components provide the functionality. As an example, a message logging component could be defined in CDL as follows: Component NAME SYNOPSIS MODULES INIT_RTN CFG_PARAMS HDR_FILES } INCLUDE_LOGGING { message logging Provides logMsg support logLib.o logInit (consoleFd, MAX_LOG_MSGS); MAX_LOG_MSGS logLib.h For illustrative purposes, in another configuration system using #ifdef/#endif statements, the definition of the logging component might look like this: #ifdef INCLUDE_LOGGING logInit (consoleFd, MAX_LOG_MSGS); #endif /* INCLUDE_LOGGING */ The component object includes the greatest number of properties. The more commonly used properties are described below. NAME The name that appears next to the component icon in the component tree of the Workbench kernel configuration facility. SYNOPSIS A brief description of the component’s functionality, which is used in Workbench. The next four properties are all related to the configuring of code in a project: 82 2 Kernel 2.8 Custom VxWorks Components and CDFs MODULES The names of the object files that constitute the component’s code (along with any source file configlettes). For example, semShow.o is identified in the MODULES property of the INCLUDE_SEM_SHOW component. ! CAUTION: An object file must only be associated with one component, and its name must be globally unique (across the entire system). CONFIGLETTES Configlettes are source file fragments used in conjunction with parameters (see CFG_PARAMS, p.83 and 2.8.7 Parameter CDF Object, p.87). They are typically used for parameter switches (for example, to specify a number, a binary setting to true or false, and so on). Configlette definitions may include the use of macros. For example: CONFIGLETTES $(MY_PARAM)\myFile.c Where MY_PARAM may either be a build macro, or an environment variable. The default directory for configlettes is installDir/vxworks-6.x/target/config/comps/src. HDR_FILES Header files associated with your configlette code or initialization routine. These are header files that must be included in order for your configlette or initialization routine to compile. ARCHIVE The archive file in which to find object modules stored other than in the standard location. The following property provides configuration information: CFG_PARAMS A list of configuration parameters associated with the component, typically a list of preprocessor macros. Each must be described separately by its own parameter object. Also see CONFIGLETTES, p.83 and 2.8.7 Parameter CDF Object, p.87. The next group of properties control integration of the component into the system image, including initialization and dependency information. INIT_RTN A one-line initialization routine. Also see INIT_BEFORE, p.84, _INIT_ORDER, p.84, and 2.8.8 Initialization Group CDF Object, p.88. 83 2 VxWorks Kernel Programmer's Guide, 6.6 LINK_SYMS A list of symbols to look up in order to include components from an archive. REQUIRES A list of component(s) that do not otherwise have structural dependencies and must be included if this component is included. List only those components that cannot be detected from MODULES; that is, by their associated object files. For example, components with configlettes only or those that reference other components through function pointers. In this latter case, REQUIRES can specify a selection. INCLUDE_WHEN Sets a dependency to automatically include the specified component(s) when this component is included (that is, it handles nested includes). INIT_BEFORE Call the initialization routine of this component before the one specified by this property. This property is effective only in conjunction with _INIT_ORDER. Also see INIT_RTN, p.83, _INIT_ORDER, p.84, and 2.8.8 Initialization Group CDF Object, p.88. _INIT_ORDER The component belongs to the specified initialization group. This property places the specified component at the end of the INIT_ORDER property list of the initialization group object. Also see INIT_RTN, p.83, INIT_BEFORE, p.84, and 2.8.8 Initialization Group CDF Object, p.88. Like NAME and SYNOPSIS before them, the following properties also affect user presentation in Workbench: HELP List reference pages associated with the component. _CHILDREN This component is a child component of the specified folder (or selection). Also see CHILDREN, p.93. _DEFAULTS This component is a default component of the specified folder (or selection). This property must be used in conjunction with _CHILDREN. Normally, the component would be listed in the container (folder or selection) as CHILDREN & DEFAULT. The usage of the complement allows adding components to an existing container without modifying the container's CDF. 84 2 Kernel 2.8 Custom VxWorks Components and CDFs Component Template Component NAME component { // required for all components name // readable name (e.g., "foo manager"). // should be in all lower case. SYNOPSIS desc // one-line description MODULES m1 m2 .. // // // // // // // // // // // object modules making up the service. used to generate dependency information. it is important to keep this list small,since the tool’s dependency engine assumes that the component is included if *any* of the modules are dragged in by dependency. It may make sense to split a large number of modules into several distinct components. CONFIGLETTES 1 s2 .. // // // // // source files in the component that are #included in the master configuration file. file paths are assumed to be relative to $(WIND_BASE)/target/config/comps/src HDR_FILES h1 h1 .. // // // // header files that need to be included to use this component. Typically contains prototypes for the initialization routine. CFG_PARAMS p1 p2 .. // // // // configuration parameters, typically macros defined in config[All].h, that can change the way a component works. see Parameters, below, for more info. INIT_RTN init(..) // one-line initialization routine. // if it needs to be more than one line, // put the code in a CONFIGLETTE. LINK_SYMS s1 s2 .. // // // // // reference these symbols in order to drag in the component from the archive. this tells the code generator how to drag in components that don’t need to be initialized. REQUIRES r1 r2 .. // // // // // // // // other components required. Note: dependencies are automatically calculated based on a components MODULES and LINK_SYMS. For example, because nfsLib.o calls rpcLib.o, the tool is able to figure out that INCLUDE_NFS requires INCLUDE_RPC. One only needs to list requirements that cannot be detected from 85 2 VxWorks Kernel Programmer's Guide, 6.6 HELP 86 h1 h2 .. // // // // MODULE dependencies. Typically only needed for components that don’t have associated MODULES (e.g., ones with just configlettes). // // // // // // // // // // // reference pages associated with the component. The default is the MODULES and INIT_RTN of the component. For example, if the component has MODULE fooLib.o, then the manual page for fooLib is automatically associated with the component (if the manual page exists). Similary for the components INIT_RTN. If there are any other relevant manual pages, they can be specified here. ARCHIVE a1 // // // // // // // // // // // // // // // // // // // // // // // // archive in which to find the MODULES. default is lib$(CPU)$(TOOL)vx.a. file path is assumed to be relative to $(WIND_BASE)/target/lib. any archive listed here is automatically added to the VxWorks link-line when the component is included. Note: the tool only analyzes archives associated with included components. This creates a chicken-and-egg problem, because the tool analyzes components before they are actually added. So if you add a component with an ARCHIVE, analysis will be done without the ARCHIVE. As a work-around, if a separate archive is used, create a dummy component that lets the tool know that a new archive should be read. Such a component should be called INSTALL_something. It should contain only NAME, SYNOPSIS, and ARCHIVE attributes. Only after the user adds it can he or she add other components from the archive. INCLUDE_WHEN c1 c2 .. // // // // // // // // // automatically include this component when some other components are included. All listed components must be included to activate the INCLUDE_WHEN (AND relationship). This allows, for example, msgQShow to be included whenever msgQ and show are included. Similarly, WDB fpp support can be included when WDB and fpp are included. INIT_BEFORE c1 // if component c1 is present, our init // routine must be called before c1. // Only needed for component releases. 2 Kernel 2.8 Custom VxWorks Components and CDFs _CHILDREN _INIT_ORDER fname // Component is a child of folder or // selection fname. gname // // // // Component is a member of init group gname and is added to the end of the initialization sequence by default (see INIT_BEFORE). } ! WARNING: The _INIT_ORDER and _CHILDREN elements should refer to elements that have already been defined. If a component is a _CHILDREN element of a folder that does not exist, it will not be displayed in the IDE. 2.8.7 Parameter CDF Object Parameters are one of the primary means of configuring a component. Typically, one or more parameters control a component’s features. Also see CONFIGLETTES, p.83 and CFG_PARAMS, p.83. For example, the following parameter defines the maximum number of log messages in the logging queue: Parameter NAME TYPE DEFAULT } MAX_LOG_MSGS { max # queued messages uint 50 This is comparable to the C code macro assignment: #define MAX_LOG_MSGS 50 Parameter Properties The following properties describe a parameter: NAME The name that appears in the Workbench. TYPE The type of parameter, which can be defined as int, uint, bool, string, exists, or untyped. When a configuration parameter is defined as type of exists the prjParams.h file that is automatically generated as part of creating a project will contain either an #define or #undef statement for the parameter. 87 2 VxWorks Kernel Programmer's Guide, 6.6 For example, the kernel configuration parameter INCLUDE_CONSTANT_RDY_Q has a type of exists. Thus, if it's value is set to TRUE (which is the default), the following will appear in the auto-generated prjParams.h file: #define INCLUDE_CONSTANT_RDY_Q If the value is set to FALSE, the following will appear: #undef INCLUDE_CONSTANT_RDY_Q DEFAULT The default value of the parameter. Parameter Template parameter name { // readable name (e.g., "max open files") SYNOPSIS desc // one-line description. STORAGE storage // MACRO, REGISTRY, ... Default is MACRO. TYPE type // // // // type of parameter: int, uint, bool, string, exists. Default is untyped. more types will be added later. DEFAULT value // // // // // // default value of the parameter. default is none - in which case the user must define a value to use the component. for parameters of type "exists," the value is TRUE if the macro should be defined, or FALSE if undefined. Parameter NAME } 2.8.8 Initialization Group CDF Object A component must include information that controls how it is integrated into an executable system image. This means that an initialization routine must be identified, as well as the point in the initialization sequence that the routine should be called. Initialization groups assemble related components for initialization and, thus, define the system startup sequence. The definition of the initialization group hierarchy is related only to run-time behavior, and has no impact on GUI presentation. Also see INIT_RTN, p.83, INIT_BEFORE, p.84, and _INIT_ORDER, p.84. 88 2 Kernel 2.8 Custom VxWorks Components and CDFs An initialization group is a routine from which components and other initialization groups are called. The code in the routine is determined by the included components and their initialization code fragments. For example: InitGroup INIT_RTN SYNOPSIS INIT_ORDER usrIosExtraInit { usrIosExtraInit(); extended I/O system INCLUDE_EXC_TASK \ INCLUDE_LOGGING \ INCLUDE_PIPES \ ... } In this example, the components INCLUDE_EXC_TASK, INCLUDE_LOGGING, and INCLUDE_PIPES are part of the initialization group usrIosExtraInit. If those components are included, then their initialization routines are called in the order specified as part of this initialization group. The code in an initialization group is synthesized by the configuration facility into the file prjConfig.c, which always part of every BSP project. To see a system’s initialization sequence, build the project and examine the generated code in prjConfig.c. Initialization Group Properties The following properties describe an initialization group: NAME The NAME property can be used to provide a short name for the initialization group; however, it does not appear anywhere in this release of the GUI. SYNOPSIS The SYNOPSIS property is used to provide a brief, readable definition of the initialization group. INIT_RTN The initialization routine that initializes an associated component(s). INIT_ORDER Components and initialization groups belonging to this initialization group listed in the order in which they are to be initialized. 89 2 VxWorks Kernel Programmer's Guide, 6.6 Initialization Group Template group rtn(..) { // initialization routine definition INIT_ORDER i1 i2 .. // ordered list of init groups and // components that belong to this init group INIT_AFTER i2 i2 .. // Only needed for component releases. InitGroup INIT_RTN } 2.8.9 Bundle CDF Object Bundle object can be used to associate components that are often used together, which facilitates configuration of the operating system with generic sets of facilities. For example, the network kernel shell (BUNDLE_NET_SHELL) includes all the components are required to use the kernel shell with a network symbol table: Bundle BUNDLE_NET_SHELL { NAME network kernel shell SYNOPSIS Kernel shell tool with networking symbol table HELP shell windsh tgtsvr COMPONENTS INCLUDE_SHELL \ INCLUDE_LOADER \ INCLUDE_DISK_UTIL \ INCLUDE_SHOW_ROUTINES \ INCLUDE_STAT_SYM_TBL \ INCLUDE_DEBUG \ INCLUDE_UNLOADER \ INCLUDE_MEM_SHOW \ INCLUDE_SYM_TBL_SHOW \ INCLUDE_CPLUS \ INCLUDE_NET_SYM_TBL _CHILDREN FOLDER_BUNDLES } For information about components, see 2.8.6 Component CDF Object, p.81. Bundle Properties NAME The name of the bundle as it should appear in Workbench. SYNOPSIS A description of the bundle’s functionality, as it should appear in Workbench. 90 2 Kernel 2.8 Custom VxWorks Components and CDFs HELP HTML help topics that the bundle is related to. 2 COMPONENTS A list of components to add to the kernel configuration when this bundle is added. _CHILDREN This bundle is a child of the specified folder. 2.8.10 Profile CDF Object A profile defines a set of components to be used as a starting point to create a project. The profile can only be used at creation time. When used, the profile replace any default configuration. Components defined by the profile are added to the project as if they were added by the user. Therefore, after creation of the project, there is no trace of the profile in the project. A profile, as such, cannot be removed. Profiles can be based on other profiles and add to them. There is a special base profile defined as BSP_DEFAULT that represents the default set of components defined by each BSP. If BSP_DEFAULT is not listed in PROFILES, then none of the BSP default components will be included in the project and the profile will replace the default configuration. Profile Properties NAME The name of the profile as it should appear in Workbench. SYNOPSIS A brief description of the profiles functionality, which is used in Workbench. PROFILES A list of base profiles. COMPONENTS A list of components to add to the kernel configuration when this profile is added. Profile Template Profile NAME profileName { nameForGui 91 VxWorks Kernel Programmer's Guide, 6.6 SYNOPSIS PROFILES COMPONENTS description p1 p2 p3... comp1 comp2 comp3... } 2.8.11 Folder CDF Object A folder is used to control the display of components in the Workbench kernel configuration facility. The Workbench component hierarchy uses folders to group components logically. Instead of presenting all components in a flat list, it presents them hierarchically. For example, top-level folders might organize components under headings such as network, drivers, OS, and so on. Folder objects provide a directory-type hierarchy for grouping components that are logically related. Folders allows for the graphical presentation of useful information about each component, such as: ■ any hierarchical grouping it has with related components ■ its associated dependencies on other components ■ its configurable properties ■ its integration into an existing system (for component releases) Folder information only affects user presentation. It is not related to initialization group hierarchy, and thereby the startup sequence, which depend solely on a component’s initialization group. Folders can contain one or more components, selections, and other folders; they do not have parameter or initialization group objects associated with them. Folders can contain more than one component. For example, the ANSI functionality contained in a folder might be described as follows: 92 2 Kernel 2.8 Custom VxWorks Components and CDFs Folder FOLDER_ANSI { NAME SYNOPSIS CHILDREN DEFAULTS ANSI C components (libc) ANSI libraries INCLUDE_ANSI_ASSERT \ INCLUDE_ANSI_CTYPE \ INCLUDE_ANSI_LOCALE \ INCLUDE_ANSI_MATH \ INCLUDE_ANSI_STDIO \ INCLUDE_ANSI_STDLIB \ INCLUDE_ANSI_STRING \ INCLUDE_ANSI_TIME \ INCLUDE_ANSI_STDIO_EXTRA INCLUDE_ANSI_ASSERT INCLUDE_ANSI_CTYPE \ INCLUDE_ANSI_MATH INCLUDE_ANSI_STDIO \ INCLUDE_ANSI_STDLIB INCLUDE_ANSI_STRING \ INCLUDE_ANSI_TIME } Folders offer great flexibility in grouping components. They allow groups to include more than just a default set of components that are included together. Components can be added and removed from the configuration individually (as defined by the CHILDREN property of the folder object). Folder Properties The following properties describe a folder: NAME The name that appears next to the folder icon in the Workbench component hierarchy. SYNOPSIS A brief description of the folder. CHILDREN Components, folders, and selections belonging to this folder are called children. Also see _CHILDREN, p.84. DEFAULTS The default component(s) that would be included if the folder were added without any overrides. Folder groupings can affect configuration when a folder is added, because components specified by a folder’s DEFAULTS property are added all at once. 93 2 VxWorks Kernel Programmer's Guide, 6.6 NOTE: Use folder objects only when creating a new grouping of components (new or existing). Do not modify existing folders in order to include new components. CDL accommodates that by prepending an underscore to a property name, for example, _CHILDREN. Folder Template folder name { // readable name (e.g., "foo libraries"). SYNOPSIS desc // one-line description CHILDREN i1 i2 .. // containers and components // that belong to this container. DEFAULTS i1 i2 .. // // // // // // // // // Folder NAME default CHILDREN. if the folder represents a complex subsystem (such as the WDB agent), this is used to suggest to the user which components in the folder are considered "default." That way the user can add the whole subsystem at once, and a reasonable set of subcomponents will be chosen. } 2.8.12 Selection CDF Object A selection is used to display alternative options in the Workbench kernel configuration facility. They are similar to folders, but they are components that implement a common interface, for example, serial drivers, the timestamp mechanism, and the WDB communication interface. These components provide alternatives for the same service, and one or more can be selected for configuration in a single project. The selections CDL class is comparable to #ifdef/#else constructs in other configuration systems. Selection information, like that for folders, is for user presentation only. It is not related to initialization group hierarchy, and thereby the startup sequence. Selections contain one or more components only. Selections behave like folders, except they add a count for a range of available components; for example, a selection containing three components might tell the user only one can be configured at a time, or perhaps two of three. Because of the 94 2 Kernel 2.8 Custom VxWorks Components and CDFs count, selections do not contain folders or other selections; nor do they have parameter or initialization group objects associated with them. 2 Selection Properties The following properties describe a selection: NAME A readable name, the one that appears next to the selection icon in the Workbench component hierarchy. SYNOPSIS A brief description of the selection. COUNT Set a minimum and maximum count from available options. CHILDREN Components from which to select. DEFAULTS The default component(s), depending on the count. For example, the following example provides for selection from a set of timestamp drivers, for use with the timestamp component: Selection NAME COUNT CHILDREN DEFAULTS SELECT_TIMESTAMP { select timestamping 1-1 INCLUDE_SYS_TIMESTAMP \ INCLUDE_USER_TIMESTAMP \ INCLUDE_SEQ_TIMESTAMP INCLUDE_SEQ_TIMESTAMP } There are three timestamp drivers available, as indicated by the three values for the CHILDREN property. The COUNT permits a choice of one, that is, a minimum and a maximum of 1. Selection Template Selection NAME SYNOPSIS selection name { // readable name (for example , "foo // communication path") desc // one-line description 95 VxWorks Kernel Programmer's Guide, 6.6 COUNT min-max // range of allowed subcomponents. // 1-1 means exactly one. // 1- means one or more. CHILDREN i1 i2 .. // components from which to select DEFAULTS i1 i2 .. // default CHILDREN. // this is not used for anything except to // to suggest to the user which components // in the selection we consider "default." } 2.8.13 CDF Template This template includes all objects and properties that can be used in a CDF. Generally, CDFs use only a portion of them. Bundle MY_BUNDLE { COMPONENTS : HELP : NAME : SYNOPSIS : _CHILDREN : } Component MY_COMPONENT { ARCHIVE : CFG_PARAMS : CONFIGLETTES : ENTRY_POINTS : EXCLUDE_WHEN : HDR_FILES : HELP : HIDE_UNLESS : INCLUDE_WHEN : INIT_AFTER : INIT_BEFORE : INIT_RTN : LINK_DATASYMS : LINK_SYMS : MODULES : NAME : PREF_DOMAIN : PROJECT : PROTOTYPE : REQUIRES : SHUTDOWN_RTN : SYNOPSIS : TERM_RTN : USES : _CHILDREN : 96 2 Kernel 2.8 Custom VxWorks Components and CDFs _COMPONENTS : _DEFAULTS : _EXCLUDE_WHEN : _HIDE_UNLESS : _INCLUDE_WHEN : _INIT_AFTER : _INIT_BEFORE : _INIT_ORDER : _LINK_DATASYMS : _LINK_SYMS : _REQUIRES : _USES : } 2 EntryPoint MY_ENTRYPOINT { NAME : PRIVILEGED : SYNOPSIS : TYPE : _ENTRY_POINTS : } EntryPointType MY_ENTRYPOINTTYPE { SYNOPSIS : _TYPE : } Folder MY_FOLDER { CHILDREN : DEFAULTS : HELP : NAME : SYNOPSIS : _CHILDREN : _DEFAULTS : } InitGroup MY_INITGROUP { HELP : INIT_AFTER : INIT_BEFORE : INIT_ORDER : INIT_RTN : NAME : PROTOTYPE : SHUTDOWN_RTN : SYNOPSIS : TERM_RTN : _INIT_AFTER : _INIT_BEFORE : _INIT_ORDER : } 97 VxWorks Kernel Programmer's Guide, 6.6 Module MY_MODULE { ENTRY_POINTS : NAME : SRC_PATH_NAME : _MODULES : } Parameter MY_PARAMETER { DEFAULT : HELP : NAME : STORAGE : SYNOPSIS : TYPE : VALUE : _CFG_PARAMS : } Profile MY_PROFILE { COMPONENTS : HELP : NAME : SYNOPSIS : _CHILDREN : } Selection MY_SELECTION { ARCHIVE : CFG_PARAMS : CHILDREN : CONFIGLETTES : COUNT : DEFAULTS : HDR_FILES : HELP : HIDE_UNLESS : INIT_AFTER : INIT_BEFORE : INIT_RTN : LINK_DATASYMS : LINK_SYMS : MODULES : NAME : PROTOTYPE : REQUIRES : SHUTDOWN_RTN : SYNOPSIS : USES : _CHILDREN : _DEFAULTS : _HIDE_UNLESS : 98 2 Kernel 2.8 Custom VxWorks Components and CDFs _INIT_AFTER : _INIT_BEFORE : _INIT_ORDER : _LINK_DATASYMS : _LINK_SYMS : _REQUIRES : _USES : } 2 Symbol MY_SYMBOL { _LINK_DATASYMS : _LINK_SYMS : } 99 VxWorks Kernel Programmer's Guide, 6.6 2.9 Custom System Calls The VxWorks system call interface provides kernel services for applications that are executed as processes in user space. The interface can be easily extended developers who wish to add custom system calls to the operating system to support special needs of their applications. (See the VxWorks Application Programmer’s Guide: Applications and Processes for information about user-space applications.) Initially, the developer’s main tasks in extending the system call interface are designing the custom system call in accordance with the naming, numbering, and argument guidelines, and then writing the system call handler to support that design. See 2.9.2 System Call Requirements, p.101 and 2.9.3 System Call Handler Requirements, p.105. The system call interface can then be extended either statically and dynamically. Static extension involves the use of configuration files and build system facilities to create a VxWorks system image that includes the new system call functionality. Dynamic extension involves using the host or kernel shell, and kernel object module loader, to download a development version of the system call handler to the kernel. See 2.9.4 Adding System Calls, p.107 and 2.9.5 Monitoring And Debugging System Calls, p.114. 2.9.1 How System Calls Work System calls are C-callable routines. They are implemented as short pieces of assembly code called system call stubs. The stubs execute a trap instruction, which switches execution mode from user mode to kernel mode. All stubs are identical to each other except for the unique system call number that they pass to the kernel to identify the system call. In kernel mode, a trap handler copies any system call arguments from the user stack to the kernel stack, and then calls the system call handler. Each system call handler is given only one argument—the address of its argument array. Handler routines interpret the argument area as a structure whose members are the arguments. System call handlers may call other routines in the kernel to service the system call request. They must validate the parameters of the system call, and return errors if necessary. 100 2 Kernel 2.9 Custom System Calls The architecture of the system call dispatcher allows system call handlers to be installed at either compile time or run-time. 2 2.9.2 System Call Requirements In order to be able to generate system calls automatically, as well as to ensure proper run-time operation, system calls must adhere strictly to naming, numbering, argument, and return value rules. System Call Naming Rules The names of various elements associated with a system call must derive their names from that of the system call itself. It is important to adhere to this convention in order to avoid compilation errors when using the automated mechanisms provided for adding system calls. See Table 2-7. Table 2-7 System Call Naming Conventions Element Name Convention system call sysCallName( ) system call stub SYSCALL_STUB_sysCallName.s system call handler routine sysCallNameSc( ) system call argument structure sysCallNameScArgs The system call name is used by developer in system call definition files. The system call stub is generated automatically from the information in the definition files. The developer must write the system call handler routine, which includes the system call argument structure. For example, if the name of the system call is foo( ), then: ■ The system call stub is named SYSCALL_STUB_foo.s. The stub implements the routine foo( ) in user mode. ■ The system call handler routine for system call foo must be named fooSc( ). Routine fooSc( ) is called when an application makes a call to foo( ) in user space. Writing a routine with this name is the kernel developer’s 101 VxWorks Kernel Programmer's Guide, 6.6 responsibility. Unless fooSc( ) exists, an error will be generated when the kernel is rebuilt. ■ If the foo system call takes at least one argument, the argument structure for foo must be declared as struct fooScArgs in the system call handler. For information about system call handler requirements, see 2.9.3 System Call Handler Requirements, p.105. For information about adding system calls to the operating system—both statically and dynamically—see 2.9.4 Adding System Calls, p.107. System Call Numbering Rules Each system call must have a unique system call number. The system call number is passed by the system call stub to the kernel, which then uses it to identify and execute the appropriate system call handler. A system call number is a concatenation of two numbers: ■ the system call group number ■ the routine number within the system call group The group number is implemented as a ten-bit field, and the routine number as a six-bit field. This allows for up to 1024 system call groups, each with 64 routines in it. The total system-call number-space can therefore accommodate 65,536 system calls. Six system call groups—numbers 2 through 7—are reserved for customer use. (Customers may request a formal system call group allocation from Wind River.) All other system call groups are reserved for Wind River use. ! WARNING: Do not use any system call group numbers other than those reserved for customer use. Doing so may conflict with Wind River or Wind River partner implementations of system calls. Wind River system call group numbers and system call routine numbers are defined in the syscallNum.def file. It should not be modified by customers. Customer system calls group numbers and system call routine numbers are defined in the syscallUsrNum.def file. The Wind River system call number definition file, and a template for the customer system call definition file are located in installDir/vxworks-6.x/target/share/h. 102 2 Kernel 2.9 Custom System Calls A given system call group is simply a collection of related system calls offering complementary functionality. For example, the VxWorks SCG_STANDARD group includes system calls that are commonly found in UNIX-like (POSIX) systems, and the SCG_VXWORKS group includes system calls that are unique to VxWorks or that are otherwise dissimilar to UNIX-like system calls. For information about using the system call definition files to generate system calls, see Adding System Calls Statically, p.107. System Call Argument Rules System calls may only take up to eight arguments. Special consideration must be given to 64-bit arguments on 32-bit systems. Floating point and vector-type arguments are not permitted. Wind River system calls are defined in the syscallApi.def file. It should not be modified by customers. Customer system calls are defined in the syscallUsrApi.def file. See Adding System Calls Statically, p.107 for information about editing this file. Number of Arguments System calls can take up to a maximum of eight arguments (the maximum that the trap handler can accommodate). Each argument is expected to be one native-word in size. The size of a native-word is 32 bits for a 32-bit architecture and 64 bits for 64-bit architectures. For the great majority of system calls (which use 32 bits), therefore, the number of words in the argument list is equal to the number of parameters the routine takes. In cases where more than eight arguments are required the arguments should be packed into a structure whose address is the parameter to the system call. 64-Bit Argument Issues 64-bit arguments are permitted, but they may only be of the type long long. For 32-bit architectures, a 64-bit argument takes up two native-words on the argument list, although it is still only one parameter to the routine. There are other complications associated with 64-bit arguments to routines. Some architectures require 64-bit arguments to be aligned to either even or odd numbered registers, while some architectures have no restrictions. It is important for system call developers to take into account the subtleties of 64-bit argument passing on 32-bit systems. The definition of a system call for 103 2 VxWorks Kernel Programmer's Guide, 6.6 VxWorks requires identification of how many words are in the argument list, so that the trap handler can transfer the right amount of data from the user-stack to the kernel-stack. Alignment issues may make this less than straightforward. Consider for example, the following routine prototypes: int foo (int a, int b, long long c, int d); int bar (int p, long long q, int r); The ARM and Intel x86 architectures have no alignment constraints for 64-bit arguments, so the size of the argument list for foo( ) would be five words, while the size of the argument for bar( ) would be four words. PowerPC requires long long arguments to be aligned on eight-byte boundaries. Parameter c to routine foo( ) is already at an eight-byte offset with respect to the start of the argument list and is hence aligned. So for PowerPC, the argument list size for foo( ) is five words. However, in the case of bar( ) the long long argument q is at offset four from the first argument, and is therefore not aligned. When passing arguments to bar, the compiler will skip one argument register and place q at offset eight so that it is aligned. This alignment pad is ignored by the called routine, though it still occupies space in the argument list. Hence for PowerPC, the argument list for bar is five words long. When describing a system call such as bar( ), it is thus advised that the argument list size be set to five for it to work correctly on all architectures. Consult the architecture ABI documentation for more information. There are only a few routines that take 64-bit arguments. System Call Return Value Rules System calls may return only a native word as a return value (that is, integer values or pointers, and so on). 64-bit return values are not permitted directly, though they may be emulated by using private routines. To do so, a system call must have a name prefixed by an underscore, and it must a pointer to the return value as one of the parameters. For example the routine: long long get64BitValue (void) must have a companion routine: void _get64BitValue (long long *pReturnValue) 104 2 Kernel 2.9 Custom System Calls Routine _get64BitValue( ) is the actual system call that should be defined in the syscallUsrNum.def and syscallUsrApi.def files. The routine get64BitValue( ) can then be written as follows: long long get64BitValue (void) { long long value; _get64BitValue (&value); return value; } (The get64BitValue( ) routine would be written by the user and placed in a user mode library, and the _get64BitValue( ) routine would be generated automatically; see 2.9.4 Adding System Calls, p.107.) The value -1 (ERROR) is the only permitted error return value from a system call. No system call should treat -1 as a valid return value. When a return value of -1 is generated, the operating system transfers the errno value correctly across the trap boundary so that the user-mode code has access to it. If NULL must be the error return value, then the system call itself must be implemented by another routine that returns -1 as an error return. The -1 value from the system call can then be translated to NULL by another routine in user mode. 2.9.3 System Call Handler Requirements System call handlers must adhere to naming conventions, and to organizational requirements for the system call argument structure. They should validate arguments. If an error is encountered, they set errno and return ERROR. A system call handler typically calls one or more kernel routines that provide the functionality required. In some cases, the code will call the public kernel API directly; in other cases, it may do otherwise to skip the kernel level validation, and call the underlying functionality directly. ! CAUTION: In order to enforce isolation between kernel and user space, not all kernel APIs may be called from a system call handler. In particular, APIs cannot be called if their operation involves passing a user-side task ID or an RTP ID. APIs also cannot be called to create objects in the kernel if those APIs are already directly accessible in user space by way of the standard system call interface. Examples include taskSpawn( ), taskCreate( ), msgQCreate( ), pthread_create( ), the various semaphore creation routines, and so on. 105 2 VxWorks Kernel Programmer's Guide, 6.6 System Call Handler Naming Rules System call handlers must be named in accordance with the system call naming conventions, which means that they must use the same name as the system call, but with an Sc appended. For example, the foo( ) system call must be serviced by the fooSc( ) system call handler. All system call handlers take a single parameter, which is a pointer to their argument structure. The argument structure must also be named in accordance with the system call naming conventions, which means that they must use the same name as the system call handler, but with Args appended. For example, the argument structure for fooSc must be declared as struct fooScArgs. For example, the write( ) system call is declared as: int write (int fd, char * buf, int nbytes) The system call handler routine for write is therefore named writeSc( ), and it is declared as: int writeSc (struct writeScArgs * pArgs) And the argument structure is writeScArgs, which is declared as: struct writeScArgs { int fd; char * buf; int nbytes; }; See System Call Naming Rules, p.101. System Call Handler Argument Validation A system call handler should validate all arguments. In particular, it should: ■ Bounds-check numerical values. ■ Validate any memory addresses to ensure they are accessible within the current memory context (that is memory within the process, and not within the kernel). See the scMemValidate( ) API reference entry for information on pointer validation across system calls. 106 2 Kernel 2.9 Custom System Calls System Call Handler Error Reporting At the end of the system call, in the case of failure, the system call handler should ensure errno is set appropriately, and then return -1 (ERROR). If the return value is -1 (ERROR) the kernel errno value is then copied into the calling process’ errno. If there is no error, simply return a value that will be copied to user mode. If the handlers set their errno before returning ERROR, user mode code sees the same errno value. 2.9.4 Adding System Calls System calls can be added both statically and dynamically. This means that they can be either configured and built into the VxWorks operating system image, or they can be added interactively to the operating system while it is running on a target. Dynamic addition is useful for rapid prototyping and debugging of system calls. Static configuration is useful for more stable development efforts, and production systems. Adding System Calls Statically The process of adding system calls statically is based on the use of the syscallUsrNum.def and syscallUsrApi.def system call definition files. The files define the system call names and numbers, their prototypes, the system call groups to which they belong, and (optionally) the components with which they should be associated. The scgen utility program uses these files—along with comparable files for standard VxWorks system calls—to generate the system call apparatus required to work with the system call handler written by the developer. The scgen program is integrated into the build system, and is run automatically when the build system detects that changes have been made to syscallUsrNum.def and syscallUsrApi.def. The template files syscallUsrNum.def.template and syscallUsrApi.def.template are in installDir/vxworks-6.x/target/share/h. Make copies of files in the same directory without the .template extension, and create the appropriate entries in them, as described below. After you have written a system call handler, the basic steps required to add a new system call to VxWorks are: 107 2 VxWorks Kernel Programmer's Guide, 6.6 1. If you are creating a new system call group, add an entry for the group to syscallUsrNum.def. See Defining a New System Call Group, p.109. Remember that only groups 2 through 7 are available to developers; do not use any other group numbers. (Contact Wind River if you need to have a group formally added to VxWorks.) 2. Add an entry to syscallUsrNum.def to assign the system call to a system call group, and to associate the system call name with a system call number. See Defining a New System Call, p.110. 3. Add an entry to syscallUsrApi.def to define the system call name and its arguments. See Defining a New System Call, p.110. 4. Write the system call handler routine. See 2.9.3 System Call Handler Requirements, p.105. 5. Rebuild the kernel-mode and user-mode source code trees installDir/vxworks-6.x/target/src and installDir/vxworks-6.x/target/usr/src. Use the following command in each directory: make CPU=cpuType TOOL=toolType This command automatically detects changes in syscallUsrNum.def and syscallUsrApi.def, invokes the scgen utility, and then rebuilds the source trees. What scgen Does Using the system call definitions in the both Wind River and the customer system call definition files scgen generates the following: 1. The files installDir/vxworks-6.x/target/h/syscall.h and installDir/vxworks-6.x/target/usr/h/syscall.h. The contents of both files are identical. They define all system call numbers and group numbers in the system. These files provide information shared between kernel and user space code. 2. One system call assembly stub file for each system call. The stubs are placed into the appropriate architecture directory under installDir/vxworks-6.x/target/usr/src/arch for compilation into libvx.a or libc.so. 3. A file containing argument structures for all system calls in the system. This file is architecture/ABI specific, and is used by the system call handlers located in the kernel. This file is named syscallArgsArchAbi.h under installDir/vxworks-6.x/target/h/arch/archName (for example, installDir/vxworks-6.x/target/h/arch/ppc/syscallArgsppc.h). 108 2 Kernel 2.9 Custom System Calls 4. A file containing a pre-initialized system call group table for all system call groups known at compile-time. This file is installDir/vxworks-6.x/target/h/syscallTbl.h. All of this output is then used by the build system automatically; no user intervention is required to build the appropriated system call infrastructure into the system. The scgen utility can also be run from the command line for debugging purposes. Defining a New System Call Group If you need to define a new system call group, add it to syscallUsrNum.def using the following syntax: SYSCALL_GROUP SCG_sgcGroupName groupNum componentNames Six system call groups—numbers 2 through 7—are reserved for customer use. All other system call groups are reserved for Wind River use. (See System Call Numbering Rules, p.102.) Group names must be unique. ! WARNING: Do not use any system call group numbers other than those reserved for customer use. Doing so may conflict with Wind River or Wind River partner implementations of system calls. Identification of component names is optional, and provides the means of associating a system call group (all its calls) with specific operating system components for inclusion in a VxWorks configuration. It works as follows: ■ If a component name is not defined, the system call group is always included in the system. ■ If a component is defined, the system call group will either be included in the system or left out of it—depending on the presence or absence of the component. That is, if the component is included in a VxWorks configuration by the user, then the system call group is included automatically. But if the component is not included in the configuration, the group is likewise not included. The fields must be separated by one or more space characters. For example, a new group called SCG_MY_NEW_GROUP could be defined with the following entry (where N is the group number selected for use): SYSCALL_GROUP SCG_MY_NEW_GROUP N INCLUDE_FOO 109 2 VxWorks Kernel Programmer's Guide, 6.6 The system calls that are part of the system call group are identified below the SYSCALL_GROUP definition line. Up to 64 system calls can be identified within each group. See Defining a New System Call, p.110. Defining a New System Call To define a new system call, you must create entries in two different files: ■ One entry in syscallUsrNum.def, which assigns it to a system call group and associates the system call name and number. ■ One entry in syscallUsrApi.def, which defines the system call name and its arguments. System Call Definition Syntax To add a system call to a call group, add an entry to syscallUsrApi.def under the appropriate system call group name, using the following syntax: sysCallNum sysCallName Note that it is important to add system calls to the end of a system call group; do use numbers that have already been assigned. Reusing an existing number will break binary compatibility with existing binaries; and all existing applications must be recompiled. System call numbers need not be strictly sequential (that is there can be gaps in the series for future use). To define a system call itself, add an entry to syscallUsrApi.def using the following syntax: sysCallName numArgs [ argType arg1; argType arg2; argType angN; ] \ CompName INCLUDE headerFileName.h System call definition lines can be split over multiple lines by using the backslash character as a connector. The name of the system call used in syscallUsrApi.def must match the name used in syscallUsrNum.def. When defining the number of arguments, take into consideration any 64-bit arguments and adjust the number accordingly (for issues related to 64-bit arguments, see System Call Argument Rules, p.103). The arguments to the system call are described in the bracket-enclosed list. The opening bracket must be followed by a space; and the closing bracket preceded by one. Each argument must be followed by a semicolon and then at least one space. If the system call does not take any arguments, nothing should be listed—not even the bracket pair. 110 2 Kernel 2.9 Custom System Calls More than one component name can be listed. If any of the components is included in the operating system configuration, the system call will be included when the system is built. (For information about custom components, see 2.8 Custom VxWorks Components and CDFs, p.67.) The following mistakes are commonly made when editing syscallUsrApi.def and syscallUsrNum.def, and can confuse the scgen utility: ■ No space after the opening bracket of an argument list. ■ No space before the closing bracket of an argument list. ■ No backslash at the end of a line (if the argument list continues onto the next line). ■ An empty pair of brackets that encloses no arguments at all. This will cause the generated temporary C file to have a compile error. Bear in mind that there can be no more than 64 routines in any system call group. If the system call includes the definition of a new type in a header file, the header file must be identified with the INCLUDE statement. The scgen utility must resolve all types before generating the argument structures, and this is the mechanism by which it is informed of custom definitions. For examples of how this syntax is used, see System Call Definition Example, p.111. Also consult the Wind River system call definitions files (syscallNum.def and syscallApi.def), but do not modify these files. System Call Definition Example Assume that we want to add the custom system call myNewSyscall( ) to a new system call group SCG_USGR0 (which is defined in syscallNum.def). First, create syscallUsrNum.def file by copying syscallUsrNum.def.template. Then edit the file syscallUsrNum.def, adding a system call group entry for the appropriate group, and the system call number and name under it. System call groups 2 through 7 are reserved for customer use; do not use any other group numbers. For example: SYSCALL_GROUP 1 myNewSyscall SCG_USER0 2 Then we must edit syscallUsrApi.def to define the system call itself. The C prototype for myNewSyscall( ) is: int myNewSyscall (MY_NEW_TYPE a, int b, char *c); 111 2 VxWorks Kernel Programmer's Guide, 6.6 The call has three arguments, and a type defined in a custom header file. Assume that we also want to implement the system call conditionally, depending on whether or not the component INCLUDE_FOO is configured into the operating system. The entry in syscallUsrApi.def would therefore look like this: INCLUDE myNewSyscall 3 [ MY_NEW_TYPE a; int b; char *c; ] INCLUDE_FOO Adding System Calls Dynamically You can dynamically extend the system call interface on a target by downloading a kernel object module that includes code for installing system call handlers as well as the system call handler routines themselves. You do not need to modify the system call definition files, to run scgen, or to rebuild the kernel. This approach is useful for rapid prototyping. It would rarely be useful or advisable with a deployed system. System Call Installation Code The code required to install your system call handlers in the kernel consists of: ■ an initialized table for the system call handler routines ■ a call to a system call registration routine This code should be included in the same module with the system call handlers. You must identify a system call group for the system calls, and it should be a group that is otherwise unused in the target system. Routine Table The system call handler routine table is used to register the system call handler routines with the system call infrastructure when the module is downloaded. For example, if the system handler routines are testFunc0( ), testFunc1( ), testFunc2( ), and testFunc3( ),the table should be declared as follows: _WRS_DATA_ALIGN_BYTES(16) SYSCALL_RTN_TBL_ENTRY testScRtnTbl [] = { {(FUNCPTR) testFunc0, 1, "testFunc0", 0}, /* routine {(FUNCPTR) testFunc1, 2, "testFunc0", 1}, /* routine {(FUNCPTR) testFunc2, 3, "testFunc0", 2}, /* routine {(FUNCPTR) testFunc3, 4, "testFunc0", 3} /* routine } 112 0 1 2 3 */ */ */ */ 2 Kernel 2.9 Custom System Calls The _WRS_DATA_ALIGN_BYTES(16) directive instructs the compiler/linker to align the table on a 16-byte boundary. This directive is optional, but is likely to improve performance as it increases the chance of locating the table data on a cache line boundary. Building the Object Module Build the object module containing the system call handlers and registration code as you would any module. See 2.6.6 Building Kernel Application Modules, p.62. Downloading the Module and Registering the System Calls After you have built the module, download it, register it, and check that registration has been successful: 1. Download it to the target system with the debugger, host shell, or kernel shell. From the shell (using the C interpreter) the module foo.o could be loaded as follows: -> ld < foo.o 2. Register the new handlers with the system call infrastructure before any system calls are routed to your new handlers. This is done by calling syscallGroupRegister( ). For example: -> syscallGroupRegister (2, "testGroup", 4, &testScRtnTbl, 0) The first argument is a variable holding the group number (an integer); the second is the group name; the second is the group name; the third is the number of system handler routines, as defined in the table; the fourth is the name of the table; and the last is set to that the registration does not forcibly overwrite an existing entry. (Note that you use the ampersand address operator with the third argument when you execute the call from the shell— which you would not do when executing it from a program.) It is important to check the return value from syscallGroupRegister( ) and print an error message if an error was returned. See the API reference for syscallGroupRegister( ) for more information. 3. Verify that the group is registered by running syscallShow( ) from the shell (host or kernel). The system call infrastructure is now ready to route system calls to the newly installed handlers. 113 2 VxWorks Kernel Programmer's Guide, 6.6 Making System Calls from a Process The quickest method of testing a new system call is to create and run a simple RTP application First, calculate the system call numbers for your new system calls. In order to do so, use the SYSCALL_NUMBER( ) utility macro (defined in syscall.h). For example, if you used group number 2 for your test group and the routine number for testFunc0( ) is 0 (as described above), then the system call number for this routine is the value returned by the following call: SYSCALL_NUMBER (2, 0) The system call number for testFunc1( ) is the value returned by this call: SYSCALL_NUMBER (2, 1) And so on. To make the actual system calls, the application calls the syscall( ) routine. The first eight arguments (all integers) are the arguments passed to your system call, and the ninth argument is the system call number. For example, to have your user-mode applications to call testFunc0( ) from process, you should implement testFunc0( ) like this: int testFunc0 ( int arg1, int arg2, int arg3, int arg4, int arg5 ) { return syscall (arg1, arg2, arg3, arg4, arg5, 0, 0, 0, SYSCALL_NUMBER(2,0)); } Note that you must use nine arguments with syscall( ). The last argument is the system call number, and the preceding eight are for the system call arguments. If your routine takes less than eight arguments, you must use zeros as placeholders for the remainder. 2.9.5 Monitoring And Debugging System Calls This section discusses using show routines, syscallmonitor( ), and hooks for obtaining information about, and debugging, system calls. 114 2 Kernel 2.9 Custom System Calls If show routines are included in your VxWorks configuration (with the component INCLUDE_SHOW_ROUTINES), the set of system calls currently available can be displayed with the syscallShow( ) shell command with the shell’s C interpreter: -> syscallShow Group Name GroupNo -------------------------TEMPGroup 7 STANDARDGroup 8 VXWORKSGroup 9 value = 55 = 0x37 = '7' NumRtns ------6 48 31 Rtn Tbl Addr -----------0x001dea50 0x001deab0 0x001dedb0 -> syscallShow 9,1 System Call Group name: VXWORKSGroup Group Number : 9 Routines provided : Rtn# Name ------------------------0 (null) 1 (null) 2 (null) 3 msgQSend 4 msgQReceive 5 _msgQOpen 6 objDelete 7 objInfoGet 8 _semTake 9 _semGive 10 _semOpen 11 semCtl 12 _taskOpen 13 taskCtl 14 taskDelay 15 rtpSpawn 16 rtpInfoGet 17 taskKill 18 taskSigqueue 19 _timer_open 20 timerCtl 21 pxOpen 22 pxClose 23 pxUnlink 24 pxCtl 25 pxMqReceive 26 pxMqSend 27 pxSemWait 28 pxSemPost 29 pipeDevCreate 30 pipeDevDelete value = 50 = 0x32 = '2' -> Address ---------0x00000000 0x00000000 0x00000000 0x001d9464 0x001d94ec 0x001d9540 0x001d95b8 0x001d9bf8 0x001d9684 0x001d96d0 0x001d970c 0x001d9768 0x001d98b8 0x001d99dc 0x001d99d4 0x001a2e14 0x001a2e60 0x001a2ec8 0x001a2f00 0x0018a860 0x0018a8c0 0x0018a960 0x0018acf4 0x0018ae44 0x0018b334 0x0018aea0 0x0018afcc 0x0018b1fc 0x0018b0f8 0x001971a8 0x001971c4 # Arguments ----------0 0 0 5 4 5 2 4 2 1 5 4 1 4 1 6 2 2 3 4 4 4 1 2 4 6 6 3 1 3 2 115 2 VxWorks Kernel Programmer's Guide, 6.6 The syscallMonitor( ) routine allows truss style monitoring of system calls from kernel mode, on a global, or per-process basis. It lists (on the console) every system call made, and their arguments. The routine synopsis is: syscallMonitor(level, RTP_ID) If the level argument is set to 1, the system call monitor is turned on; if it is set to 0, it is turned off. If the RTP_ID is set to an RTP_ID, it will monitor only the system calls made from that process; if it is set to 0, it will monitor all system calls. The sysCallHookLib library provides routines for adding extensions to the VxWorks system call library with hook routines. Hook routines can be added without modifying kernel code. The kernel provides call-outs whenever system call groups are registered, and on entry and exit from system calls. Each hook type is represented as an array of function pointers. For each hook type, hook functions are called in the order they were added. For more information, see the syscallHookLib API reference. 2.9.6 Documenting Custom System Calls Since system calls are not functions written in C, the apigen documentation generation utility cannot be used to generate API references from source code comments. You can, however, create a function header in a C file that can be read by apigen. The function header for system calls is no different from that for other C functions. 116 2 Kernel 2.9 Custom System Calls Here is a function header for getpid( ): /*********************************************************************** * * getpid - Get the process identifier for the calling process. * * SYNOPSIS * \cs * int getpid * ( * void * ) * \ce * * DESCRIPTION * * This routine gets the process identifier for the calling process. * The ID is guaranteed to be unique and is useful for constructing * uniquely named entities such as temporary files etc. * * RETURNS: Process identifier for the calling process. * * ERRNO: N/A. * * SEE ALSO: * .pG "Multitasking" * */ No code or C declaration should follow the header. The compiler treats it as a comment block, but apigen uses it to generate API documentation. All fields in the header above (SYNOPSIS, DESCRIPTION, RETURNS, and so on) must to be present in the code. You have two choices for the location of the comments: ■ You may add system call function headers to an existing C source file (one that has code for other functions). Be sure that this source file is part of the DOC_FILES list in the makefile for that directory. The apigen utility will not process it otherwise. ■ You may create a C file that contains only function headers and no C code. Such files must be part of the DOC_FILES list in the makefile, but not part of the OBJS list (because there is no code to compile). For more information about the coding conventions that are required for API documentation generation, and the apigen tool, see the VxWorks BSP Developer’s Guide and the apigen entry in the Wind River Host Utilities API reference. 117 2 VxWorks Kernel Programmer's Guide, 6.6 2.10 Custom Scheduler VxWorks provides a scheduler framework that can be used to implement a custom scheduler. This section describes the requirements for creating a custom scheduler for VxWorks, and for configuring the operating system for its use. It also describes key features of the traditional VxWorks scheduler that provide a useful reference for designing a custom scheduler. Before you consider implementing a custom scheduler, however, you should be familiar with the schedulers provided by Wind River. They are the following: ! ■ The traditional VxWorks scheduler, which provides for priority-based preemptive scheduling, plus a round-robin extension. The traditional scheduler is included in VxWorks by default. For information, see 4.3.3 VxWorks Traditional Scheduler, p.168. ■ The VxWorks POSIX thread scheduler, which provides additional features for pthreads running in processes. For information, see 5.12 POSIX and VxWorks Scheduling, p.277. WARNING: The scheduler is fundamental to an operating system's behavior. VxWorks is not guaranteed to function as expected if a custom scheduler is used. You should ensure that all VxWorks components behave appropriately when a custom scheduler is used in place of a Wind River scheduler. NOTE: The scheduler framework is not supported for the symmetric multiprocess- ing (SMP) configuration of VxWorks. For general information about VxWorks SMP and about migration, see 15. VxWorks SMP and 15.15 Migrating Code to VxWorks SMP, p.702. 2.10.1 Requirements for a Custom Scheduler The VxWorks scheduler framework allows you to implement a custom kernel scheduler for VxWorks. This section describes the code and configuration requirements for custom schedulers. Code Requirements A custom scheduler must manage the set of tasks that are in the READY state; that is, the tasks that are eligible for execution. At a minimum, a custom scheduler must 118 2 Kernel 2.10 Custom Scheduler define a ready queue structure for all ready tasks or a hook-routine that is executed at every clock tick. A custom scheduler may also specify other class-specific structures, manage data in the task control block, and so on. Q_HEAD and Q_NODE Structures A user-specified ready queue class must define class-specific Q_NODE and Q_HEAD structures. The size of these structures together must not be more than 16 bytes. For more information, see Multi-way Queue Structure, p.124. Q_CLASS Structure and Associated Routines Users must define a ready-queue class for all READY tasks. A set of routines required by the Q_CLASS structure must be implemented. For more information about the Q_CLASS structure, see Multi-way Queue Structure, p.124. Task Control Block Data For a custom scheduler that must store user specific information in tasks, the pSchedInfo member of the task control block (TCB) may be used. The pSchedInfo member of the TCB is a void pointer. There are two ways to access pSchedInfo, as follows: ■ If the qNode is given, the TASK_QNODE_TO_PSCHEDINFO( ) macro may be used to get the address of pSchedInfo. The file installDir/vxworks-6.x/target/h/taskLib.h provides the definition of this macro. The macro is typically used in the user-defined queue management functions. For example: void customQPut ( CUSTOM_Q_HEAD *pQHead, /* head of readyQ */ CUSTOM_NODE *pQNode, /* mode of insert */ ULONG key /* key for insert */ ) { void **ppSchedInfo; /* get the address to the pSchedInFo */ ppSchedInfo = (void **) TASK_QNODE_TO_PSCHEDINFO (pQNode); } ■ If the task ID tid is given, the TASK_SCHED_INFO_SET( ) macro can be used to set the pSchedInfo field in the TCB. The macro TASK_SCHED_INFO_GET( ) 119 2 VxWorks Kernel Programmer's Guide, 6.6 can be used for getting the value of pSchedInfo. Both macros are defined in installDir/vxworks-6.x/target/h/taskUtilLib.h. The custom scheduler may use pSchedInfo as the pointer to the user-specific data structure for tasks. If so, it must allocate memory for the data structure using a task hook routine that calls malloc( ) or memalign( ). This approach, however, makes the task creation process less deterministic. The memory can also be statically allocated (using global variables) for user-specified storage, and then used it during task initialization. Tick Hook Routine If a custom scheduler performs operations at each tick interrupt, the tickAnnounceHookAdd( ) routine can be used to register a hook routine that is called at each tick interrupt. The hook routine must obey the same rules as ISRs, because it runs in interrupt context. Any VxWorks kernel service that should not be called in an interrupt context should not be called in this hook. For information about restrictions on ISRs, see 4.20 Interrupt Service Routines, p.241. The following pseudo-code example illustrates hook use: void usrTickHook ( int tid /* task ID */ ) { update the statistics information if needed; update interrupted task's time slice if needed; resort the interrupted task location in the ready queue if needed. } Custom Round-Robin Scheduling VxWorks provides a round-robin scheduling policy based on a task hook routine. A custom scheduler may use the VxWorks round-robin scheme by incorporating the kernelRoundRobinHook( ) routine in the user-specific tick hook routine. The kernelRoundRobinHook( ) routine places a task at the tail of the task list for its priority in the ready queue, and resets its time slice, if all of the following are true: 1. The interrupted task has not locked preemption. 2. The interrupted task is still in the READY state. 3. The interrupted task has consumed its allowed time slice. 120 2 Kernel 2.10 Custom Scheduler To take advantage of the VxWorks's implementation of round-robin scheduling, the kernelRoundRobinInstall( ) routine should be called in the usrCustomSchedulerInit( ) routine to install the kernelRoundRobinHook( ) call. For more information see Modify usrCustomSchedulerInit( ) Routine, p.122. The routine _func_kernelRoundRobinHook( ) can then be called within the user defined hook for the round robin policy to take effect. The _func_kernelRoundRobinHook( ) takes the task ID (tid) of the interrupted task as its argument. The following code example takes advantage of the VxWorks round-robin scheduling scheme: void usrTickHook int tid /* task interrupted by tick */ ) { /* statistic information */ /* call kernelRoundRobinHook() */ if (_func_kernelRoundRobinHook != NULL) _func_kernelRoundRobinHook (tid); /* other work */ ... } If the custom scheduler does not take advantage of the VxWorks round-robin scheduling policy using kernelRoundRobinHook( ), the routine kernelTimeSlice( ) must not be used to adjust system time slice nor to enable or disable round-robin scheduling. The kernelTimeSlice( ) routine is used to dynamically enable round robin scheduling and to set the system time slice, or to disable it. For more information about VxWorks round-robin scheduling, see Round-Robin Scheduling, p.169. Configuration Requirements To use a custom scheduler with VxWorks, the following must be done: ■ Configure VxWorks for use with a custom scheduler ■ Modify an initialization routine in a configuration file. ■ Link the custom ready queue management code with VxWorks. 121 2 VxWorks Kernel Programmer's Guide, 6.6 Add INCLUDE_CUSTOM_SCHEDULER Component To enable the custom scheduler framework, VxWorks must be configured with the INCLUDE_CUSTOM_SCHEDULER component. Modify usrCustomSchedulerInit( ) Routine The usrCustomSchedulerInit( ) routine must be modified to specify the custom ready queue structure and any hook routines that are executed at each tick interrupt. The following code illustrates this modification: void usrCustomSchedulerInit (void) { vxKernelSchedDesc.readyQClassId vxKernelSchedDesc.readyQInitArg1 vxKernelSchedDesc.readyQInitArg2 = qUserClassId; /* user’s class ID */ = (void *) &usrReadyQBMap; /* arg1 */ = (void *) 256; /* arg2 */ tickAnnounceHookAdd ((FUNCPTR)usrTickHook); kernelRoundRobinInstall(); } The usrTickHook argument is the hook to be called at each tick interrupt. The kernelRoundRobinInstall( ) call is for the user VxWorks round-robin scheduling scheme. The usrCustomSchedulerInit( ) routine is in the installDir/vxworks-6.x/target/config/comps/src/usrCustomerScheduler.c file. For information about the vxKernelSchedDesc variable, see Scheduler Initialization, p.123. This variable must be initialized for a custom scheduler. Link Custom Scheduler Code There are several ways for users to link the definition and implementation of Q_NODE, Q_HEAD, and Q_CLASS structure to VxWorks. For example, the custom scheduler configuration file installDir/vxworks-6.x/target/config/comps/src/usrCustomerScheduler.c can be the placeholder for the Q_NODE and Q_HEAD type definitions and user specified Q_CLASS implementation. Another way is to create a new header file for Q_NODE and Q_HEAD definitions and a new source file for Q_CLASS implementation, and then link the new object file to VxWorks using the EXTRA_MODULES macro. For example: EXTRA_MODULES = qUserPriLib.o For information about using the EXTRA_MODULES macro, see 2.6.8 Linking Kernel Application Object Modules with VxWorks, p.64. 122 2 Kernel 2.10 Custom Scheduler 2.10.2 Traditional VxWorks Scheduler The traditional VxWorks scheduler is the default, and is included in the system with the INCLUDE_VX_TRADITIONAL_SCHEDULER component. The traditional scheduler has a priority-based preemptive scheduling policy. A round-robin scheduling extension can be enabled with the kernelTimeSlice( ) routine. For more information about these options, see 4.3.3 VxWorks Traditional Scheduler, p.168. This section provides information about key features of the traditional VxWorks scheduler that can be useful in designing a custom scheduler. Scheduler Initialization The kernel scheduler description structure is initialized in the usrKernelInit( ) routine. The following is an example for configuring the VxWorks traditional scheduler: #ifdef INCLUDE_VX_TRADITIONAL_SCHEDULER /* install the traditional priority based preemptive scheduler */ #if (VX_TRADITIONAL_SCHED_CONSTANT_RDY_Q == TRUE) vxKernelSchedDesc.readyQClassId = Q_PRI_BMAP; vxKernelSchedDesc.readyQInitArg1 = (void *) &readyQBMap; vxKernelSchedDesc.readyQInitArg2 = (void *) 256; #else vxKernelSchedDesc.readyQClassId = Q_PRI_LIST; #endif /* VX_TRADITIONAL_SCHED_CONSTANT_RDY_Q == TRUE */ #endif /* INCLUDE_VX_TRADITIONAL_SCHEDULER */ This code is from installDir/vxworks-6.x/target/config/comps/src/usrKernel.c. The vxKernelSchedDesc variable is the kernel scheduler description structure, which is defined in installDir/vxworks-6.x/target/h/kernelLib.h as follows: typedef struct wind_sched_desc { Q_CLASS_ID readyQClassId; /* readyQ Id */ void * readyQInitArg1; /* readyQ init arg 1 */ void * readyQInitArg2; /* readyQ init arg 2 */ } WIND_SCHED_DESC; The readyQClassId is a pointer to a ready queue class. The ready queue class is a structure with a set of pointers to routines that manage tasks that are in the READY state. The readyQInitArg1 and readyQInitArg2 are the input arguments for the initRtn( ) routine of the ready queue class. 123 2 VxWorks Kernel Programmer's Guide, 6.6 The Q_PRI_BMAP value (which is assigned to vxKernelSchedDesc.readyQClassId) is the priority-based bit-mapped ready queue class ID. See Multi-way Queue Structure, p.124 for more information about the ready queue class and its associated members. The vxKernelSchedDesc can be initialized with the user-specified ready queue class for customized kernel schedulers. See 2.10.1 Requirements for a Custom Scheduler, p.118 for more information how to install custom schedulers. After the initialization of vxKernelSchedDesc variable, VxWorks invokes the qInit( ) routine to initialize the ready queue class, as follows: /* kernel scheduler ready queue init */ qInit (&readyQHead, vxKernelSchedDesc.readyQClassId, (int)(vxKernelSchedDesc.readyQInitArg1), (int)(vxKernelSchedDesc.readyQInitArg2)); The qInit( ) routine invokes vxKernelSchedDesc.readyQClassId->initRtn( ) to set up the ready queue and the readyQHead variable (which is of type Q_HEAD). It is described below in Multi-way Queue Structure, p.124. Multi-way Queue Structure The VxWorks scheduler data structure consists of Q_HEAD, Q_NODE, and Q_CLASS elements. The type definitions of Q_HEAD and Q_NODE structures are flexible so that they can be used for different types of ready queues. The readyQHead variable is the head of a so-called multi-way queue, and the aforementioned Q_PRI_BMAP queue classes comply with the multi-way queue data structures. The multi-way queue head structure (Q_HEAD) is defined in qLib.h as follows: typedef struct /* Q_HEAD */ { Q_NODE *pFirstNode; /* first node in queue based on key */ UINT qPriv1; /* use is queue type dependent */ UINT qPriv2; /* use is queue type dependent */ Q_CLASS *pQClass; /* pointer to queue class */ } Q_HEAD; The first field in the Q_HEAD contains the highest priority node. 124 2 Kernel 2.10 Custom Scheduler NOTE: Both the qFirst( ) routine and Q_FIRST( ) macro simply read the first four bytes of the Q_HEAD structure (the pFirstNode field) to determine the head of the queue. There is, therefore, no need for a queue-class specific routine to determine which node is the head of the queue. The kernel scheduler performs a Q_FIRST( ) on readyQHead to determine which task should be allocated to the CPU. For the Q_PRI_BMAP and Q_PRI_LIST queue classes, this represents the highest priority ready task. The multi-way queue node structure (Q_NODE) is also defined in qLib.h as follows: typedef struct { UINT qPriv1; UINT qPriv2; UINT qPriv3; UINT qPriv4; } Q_NODE; /* Q_NODE */ /* /* /* /* use use use use is is is is queue queue queue queue type type type type dependent dependent dependent dependent */ */ */ */ Each task control block contains a Q_NODE structure for use by a multi-way queue class to manage the set of ready tasks. This same Q_NODE is used to manage a task when it is in a pend queue. Note that a custom implementation of a multi-way queue class may define class-specific Q_HEAD and Q_NODE structures. The size of the class-specific structures must not exceed 16 bytes, which is the current size of both the Q_HEAD and Q_NODE structures. Q_CLASS Structure The kernel interacts with a multi-way queue class through a Q_CLASS structure. A Q_CLASS structure contains function pointers to the class-specific operators. For example, the address of the class specific put routine is stored in the putRtn field. As described in Scheduler Initialization, p.123, the qInit( ) routine is used to initialize a multi-way queue head to a specified queue type. The second parameter specifies the queue class (that is, the type of queue), and is merely a pointer to a Q_CLASS structure. All kernel invocations of the queue class operators are performed indirectly through the Q_CLASS structure. The Q_CLASS structure is defined in qClass.h as follows: 125 2 VxWorks Kernel Programmer's Guide, 6.6 typedef struct q_class /* Q_CLASS */ { FUNCPTR createRtn; /* create and initialize a queue */ FUNCPTR initRtn; /* initialize a queue */ FUNCPTR deleteRtn; /* delete and terminate a queue */ FUNCPTR terminateRtn; /* terminate a queue */ FUNCPTR putRtn; /* insert a node into q with insertion key */ FUNCPTR getRtn; /* return and remove lead node routine */ FUNCPTR removeRtn; /* remove routine */ FUNCPTR resortRtn; /* resort node to new priority */ FUNCPTR advanceRtn; /* advance queue by one tick routine */ FUNCPTR getExpiredRtn; /* return and remove an expired Q_NODE */ FUNCPTR keyRtn; /* return insertion key of node */ FUNCPTR calibrateRtn; /* calibrate every node in queue by an offset */ FUNCPTR infoRtn; /* return array of nodes in queue */ FUNCPTR eachRtn; /* call a user routine for each node in queue */ FUNCPTR restoreRtn; /* restore a node position in queue */ struct q_class *valid; /* valid == pointer to queue class */ } Q_CLASS; The restoreRtn operator is used in VxWorks SMP, which does not support custom schedulers. The operator must therefore be set to NULL. The following operators are not applicable to a queue class that is used to manage the set of ready tasks: advanceRtn, getExpiredRtn, and calibrateRtn. The signatures of the expected Q_CLASS operators are as follows: Q_HEAD * createRtn STATUS initRtn STATUS deleteRtn STATUS terminateRtn void putRtn Q_NODE * getRtn STATUS removeRtn void resortRtn ULONG keyRtn int infoRtn Q_NODE * eachRtn (... /* (Q_HEAD (Q_HEAD (Q_HEAD (Q_HEAD (Q_HEAD (Q_HEAD (Q_HEAD (Q_HEAD (Q_HEAD (Q_HEAD optional arguments */); *pQHead, ... /* optional arguments */); *pQHead); *pQHead); *pQHead, Q_NODE *pQNode, ULONG key); *pQHead); *pQHead, Q_NODE *pQNode); *pQHead, Q_NODE *pQNode, ULONG newKey); *pQHead, Q_NODE *pQNode, int keyType); *pQHead, Q_NODE *nodeArray [ ], int maxNodes); *pQHead, FUNCPTR routine, int routineArg); As noted above, a custom scheduler may define class-specific Q_HEAD and Q_NODE structures. Q_CLASS Operators This section provides descriptions of each Q_CLASS operator that pertains to the management of ready tasks. Each description provides information about when the kernel invokes the operator for managing ready tasks. Descriptions of the advanceRtn, getExpiredRtn, and calibrateRtn operators are not provided as they are not applicable to managing the set of ready tasks. 126 2 Kernel 2.10 Custom Scheduler Some Q_CLASS operators are invoked within the kernel context. The operator description indicate whether the operator is invoked within kernel context or not. The operators that are invoked within kernel context do not have access to all VxWorks facilities. Table 2-8 lists the routines that are available from within kernel context. Table 2-8 Kernel Context Routines VxWorks Library Available Routines blib All routines fppArchLib fppSave( ) and fppRestore( ) intLib intContext( ), intCount( ), intVecSet( ), intVecGet( ) lstLib, dllLib, sllLib All routines except xxxCreate( ) and xxxDelete( ) ! mathALib All routines, if fppSave( ) and fppRestore( ) are used rngLib All routines except rngCreate( ) taskLib taskIdVerify( ), taskIdDefault( ), taskIsReady( ),taskIsSuspended( )and taskTcb( ) vxLib vxTas( ) WARNING: The use of any VxWorks APIs that are not listed Table 2-8 from an operator that is invoked from kernel context results in unpredictable behavior. Typically the target will hang or reboot. createRtn Allocates a multi-way queue head structure from the system memory pool. The dynamically-allocated head structure is subsequently initialized. Currently the kernel does not utilize this operator. Instead, the ready task queue is initialized by statically allocating the head structure, and using the initRtn operator. initRtn Initializes a multi-way queue head. Up to ten optional arguments can be passed to the initRtn. The kernel initializes the ready task queue from the usrKernelInit( ) routine as described in Scheduler Initialization, p.123. This operator is not called from within kernel context. 127 2 VxWorks Kernel Programmer's Guide, 6.6 deleteRtn Deallocates (frees) the multi-way queue head. All queued nodes are lost. Currently the kernel does not utilize this operator. terminateRtn Terminates a multi-way queue head. All queued nodes will be lost. Currently the kernel does not utilize this operator. putRtn Inserts a node into a multi-way queue. The insertion is based on the key and the underlying queue class. The second parameter is the Q_NODE structure pointer of the task to be inserted into the queue. Recall that each task control block contains a Q_NODE structure for use by a multi-way queue class to manage the set of ready tasks. The third parameter, (the key), is the task’s current priority. Note that a task’s current priority may be different than a task’s normal priority due to the mutex semaphore priority inheritance protocol. The pFirstNode field of the Q_HEAD structure must be updated to contain the first node in the queue (if any change has occurred). The putRtn operator is called whenever a task becomes ready; that is, a task is no longer suspended, pended, delayed, or stopped (or a combination thereof). The VxWorks round-robin policy performs a removeRtn operation followed by a putRtn when a task has exceeded its time slice. In this case, the task does not change state. However, the expectation after performing a removeRtn operation followed by a putRtn operation is that the task appears as the last task in the list of tasks with the same priority, if there are any. Performing a taskDelay(0) operation also results in a removeRtn operation followed by a putRtn. Again, in this case the task does not change state, and the expectation after performing a removeRtn operation followed by a putRtn operation is that the task appears as the last task in the list of tasks with the same priority, if there are any. This operator is called from within kernel context. getRtn Removes and returns the first node in a multi-way queue. Currently the kernel does not utilize this operator. removeRtn Removes the specified node from the specified multi-way queue. 128 2 Kernel 2.10 Custom Scheduler The removeRtn operator is called whenever a task is no longer ready; that is, it is no longer eligible for execution, since it has become suspended, pended, delayed, or stopped (or a combination thereof). See the discussion of the putRtn operator above for more information about situations in which the kernel performs a removeRtn operation followed by a putRtn without the task’s state actually changing. This operator is called from within kernel context. resortRtn Resorts a node to a new position based on a new key. The resortRtn operator is called whenever a task’s priority changes, either due to an explicit priority change with the taskPrioritySet( ) API, or an implicit priority change due to the mutex semaphore priority inheritance protocol. The difference between invoking the resortRtn operator and a removeRtn/putRtn combination is that the former operator does not change the position of the task in the list of tasks with the same priority (if any) when the priority is the same as the old priority. This operator is called from within kernel context. keyRtn Returns the key of a node currently in a multi-way queue. The keyType parameter determines key style on certain queue classes. Currently the kernel does not utilize this operator. infoRtn Gathers information about a multi-way queue. The information consists of an array, supplied by the caller, filled with all the node pointers currently in the queue. Currently the kernel does not utilize this operator. eachRtn Calls a user-supplied routine once for each node in the multi-way queue. The routine should be declared as follows: BOOL routine ( Q_NODE *pQNode, int arg ); /* pointer to a queue node */ /* arbitrary user-supplied argument */ The user-supplied routine should return TRUE if qEach( ) is to continue calling it for each entry, or FALSE if it is done, and qEach( ) can exit. Currently the kernel does not utilize this operator. 129 2 VxWorks Kernel Programmer's Guide, 6.6 130 3 Boot Loader 3.1 Introduction 132 3.2 Using a Default Boot Loader 132 3.3 Boot Loader Image Types 133 3.4 Boot Loader Shell 135 3.5 Boot Loader Parameters 140 3.6 Rebooting VxWorks 145 3.7 Customizing and Building Boot Loaders 146 3.8 Installing Boot Loaders 152 3.9 Booting From a Network 152 3.10 Booting From a Target File System 154 3.11 Booting From the Host File System Using TSFS 155 131 VxWorks Kernel Programmer's Guide, 6.6 3.1 Introduction A VxWorks boot loader is an application whose purpose is to load a VxWorks image onto a target. It is sometimes called the VxWorks bootrom, but use of this term is not encouraged (it conflates application and media). Like VxWorks, the boot loader can be configured with various facilities; such a command shell for dynamically setting boot parameters, a network loader, and a file system loader. The same boot loaders are used for uniprocessor (UP), symmetric multiprocessor (SMP), and asymmetric multiprocessor (AMP), configurations of VxWorks. In a development environment, boot loaders are useful for loading a VxWorks image from a host system, where VxWorks can be quickly modified and rebuilt. They can also be used in production systems when the boot loader and operating system are stored on a disk or other media. Self-booting (standalone) VxWorks images do not require a boot loader. These images are commonly used in production systems (stored in non-volatile devices). For more information, see 2.4.1 VxWorks Image Types, p.15. Usually, the boot loader is programmed in a non-volatile device (usually flash memory or EEPROM) at an address such that it is the first code that is run by the processor when the target is powered on or rebooted. The procedure to get the boot loader programmed in a non-volatile device or written to a disk is dependent on the target, and is described in the BSP reference documentation. The VxWorks product installation includes default boot loader images for each installed BSP. If they do not meet your needs, you can create custom boot loaders. For example, you may need to use a different network driver to load the VxWorks image over your development network, or you may want to remove the boot loader shell for deployed systems. For information beyond what is in this chapter, particularly information about setting up a cross-development environment, see the Wind River Workbench User’s Guide: Setting up Your Hardware. 3.2 Using a Default Boot Loader The default boot loader is designed for a networked target and must be configured with parameters such as your host and target network addresses, the full path and 132 3 Boot Loader 3.3 Boot Loader Image Types name of the file to be loaded, the user name, and more. To use the default boot loader, you must interactively change the default parameters using the boot loader shell so that the loader can find the VxWorks image on the host and load it onto the target. After you have entered boot loader parameters, the target can be booted with the VxWorks image. For most targets, the new settings are saved (in a non-volatile device or to disk) so you can reboot the target without resetting them. You interact with the boot loader shell at a terminal console that is usually established by connecting a serial port of the target to a serial port on the host and starting a terminal application on the host. For information about the setup required to establish communication over the serial port of a particular target, see the reference documentation for the BSP in question. When you apply power to the target (or each time it is reset), the target runs the boot loader (from ROM, flash, disk, or other media). During the boot process, the target uses its serial port to communicate with the host system. The boot loader displays a banner page and then starts a seven-second countdown before booting VxWorks. You can interrupt the boot process by pressing any key in order to set the appropriate boot parameters. Default boot loader images are in installDir/vxworks-6.x/target/config/bspName. The boot loader commands and parameters are described in 3.4.1 Boot Loader Shell Commands, p.136 and 3.5 Boot Loader Parameters, p.140. The different types of boot loader images provided as defaults are described in 3.3 Boot Loader Image Types, p.133. 3.3 Boot Loader Image Types Boot loader images can be stored in ROM, flash, on disk, or in storage on a network. Boot loader images are in ELF format. Binary file versions (.bin) are used for disks, and the hex record file versions (.hex) are used for programming non-volatile devices. For information about which types are available for a specific target, see the reference documentation for the BSP in question. The varieties of boot loader images are described below. The first of each pair of file names listed for each image type is produced with the PROFILE_BOOTAPP profile, and the second by the legacy bspDir/config.h method. For more 133 3 VxWorks Kernel Programmer's Guide, 6.6 information about build methods, see 3.7 Customizing and Building Boot Loaders, p.146. Compressed Image vxWorks_romCompress and bootrom files The image is almost entirely compressed. It has a small un-compressed portion that the processor runs immediately after power is applied or the target is reset. This portion initializes memory and decompresses the compressed section (stored in non-volatile storage) into RAM, and causes the processor to switch execution to RAM. Compression of the image makes it much smaller than other types of boot loader images, therefore it uses less non-volatile storage. However, decompression increases the boot time. Uncompressed Image vxWorks_rom and bootrom_uncmp files The image is not compressed. It copies itself to RAM and makes the processor switch execution to RAM. Because the image is not compressed, it is larger than the compressed image type. However, it has faster boot time because there is no decompression operation required. Resident in Non-Volatile Storage vxWorks_romResident and bootrom_res files The image copies only the data segment to RAM on startup; the text segment stays in non-volatile storage. This means that the processor always executes instructions out of non-volatile storage. It is therefore sometimes described as being ROM-resident. This type of boot loader image is the one that requires the least amount of RAM to boot load the VxWorks kernel. It is therefore useful for boards with very little RAM, which needs to be saved for the application. Boot loader images are located in installDir/vxworks-6.x/target/config/bspName. Note that the default images for most BSPs are configured for a networked development environment. For information about creating a custom boot loader, see 3.7 Customizing and Building Boot Loaders, p.146. 134 3 Boot Loader 3.4 Boot Loader Shell 3.4 Boot Loader Shell The boot loader shell provides commands for the following activities: ■ Changing boot loader parameters (such as the host and target IP addresses) ■ Rebooting the target system ■ Managing the boot process. To include the boot loader shell, configure the boot loader with the INCLUDE_BOOT_SHELL component. ! CAUTION: Do not add any of the following components to the boot loader: ■ ■ ■ INCLUDE_WDB_BANNER INCLUDE_SIMPLE_BANNER INCLUDE_SHELL They conflict with the boot loader shell. If you include any of them, you will encounter configuration errors. When the boot loader has initiated booting the system, it prints a banner. After a countdown elapses, the boot loader loads and runs the specified image. (If the boot loader shell is not included, the loader executes with its current parameters and without a countdown.) To reset the boot parameters, interrupt the boot loader during the countdown by pressing any key before the countdown period elapses. To access the boot-loader shell prompt, power on (or reboot) the target; then stop the boot sequence by pressing any key during the seven-second countdown. The appearance of the boot-loader banner followed by keystroke interruption of the boot process looks like the following: VxWorks System Boot Copyright 1984-2005 Wind River Systems, Inc. CPU: PC PENTIUM3 Version: VxWorks 6.3 BSP version: 2.0/6 Creation date: Jun 08 2006, 12:08:39 135 3 VxWorks Kernel Programmer's Guide, 6.6 Press any key to stop auto-boot... 7 [VxWorks Boot]: To display a list of available commands, type either h or ? at the prompt, followed by ENTER. For information about the commands, see 3.4.1 Boot Loader Shell Commands, p.136. 3.4.1 Boot Loader Shell Commands The VxWorks boot loader provides a set of commands that can be executed from the boot loader shell, which are described in the following tables. For information about the boot loader shell, see 3.4 Boot Loader Shell, p.135. 136 3 Boot Loader 3.4 Boot Loader Shell Table 3-1 Commands Provided with INCLUDE_BOOT_SHELL Command Description h Help command. Print a list of available boot commands and flags; the boot device in use, image path, and image file name; and the boot devices available in the boot loader. ? Same as h. @ Boot (that is, load and execute the VxWorks image file) using the current boot parameters. See 3.5 Boot Loader Parameters, p.140. $ [ paramString ] Boot (that is, load and execute the VxWorks image file). If used without a parameter string, the command is the same as @. The parameter string can be used to set boot loader parameter values all at once, instead of interactively. See 3.5 Boot Loader Parameters, p.140 and 3.5.3 Changing Boot Loader Parameters Interactively, p.144). p Print the current boot parameter values. See 3.5 Boot Loader Parameters, p.140. c Change the boot parameter values. See 3.5 Boot Loader Parameters, p.140. l Load the VxWorks image file using current boot parameters, but without executing. g adrs Go to (execute at) hex address adrs. e Display a synopsis of the last occurring VxWorks exception. v Display boot-loader banner page with BSP and boot loader version information. 137 3 VxWorks Kernel Programmer's Guide, 6.6 Table 3-2 Commands Provided with INCLUDE_BOOT_MEM_CMDS Command Description d adrs[, n] Display n words of memory starting at hex address adrs. If n is omitted, the default is 64. m adrs Modify memory at location adrs (hex). The system prompts for modifications to memory, starting at the specified address. It prints each address, and the current 16-bit value at that address, in turn. You can respond in any of the following ways at the prompt: ENTER Pressing the ENTER key alone does not change the address specified with adrs, but continues prompting at the next address. number Entering a number sets the 16-bit contents at the memory address to that number. . Entering a . (period) leaves the address unchanged, and quits. f adrs, nbytes, value Fill nbytes of memory, starting at adrs with value. t adrs1, adrs2, nbytes Copy nbytes of memory, starting at adrs1, to adrs2. Table 3-3 Command Provided with INCLUDE_BOOT_ETH_MAC_HANDLER Command Description M [dev] [unitNo] [MAC] Set and display Ethernet MAC address. For example: M motfcc0 00:A0:1E:00:10:0A In this case, the device is motfcc, the unit number is zero, and the MAC address is 00A01E00100A. 138 3 Boot Loader 3.4 Boot Loader Shell Table 3-4 Command Provided with INCLUDE_BOOT_ETH_ADR_SET Command Description N [last3ByteValuesMAC] Set (last three bytes) and display Ethernet MAC address. NOTE: The M command (see Table 3-3) is a replacement for the N command (Table 3-4), which is maintained for backwards compatibility purposes. For information about which of the two is supported for a given BSP, consult the BSP reference. The M and N command are provided by the INCLUDE_BOOT_ETH_MAC_HANDLER and INCLUDE_BOOT_ETH_ADR_SET, respectively. Do not use both components in the same configuration of VxWorks. Table 3-5 Commands Provided with INCLUDE_BOOT_EDR_SUPPORT Command Description P Print the error log for the error detection and reporting facility. C Clear the error log for the error detection and reporting facility. For information about the error detection and reporting facility, see 11. Error Detection and Reporting. Table 3-6 Command Provided with BOOT_FILESYSTEMS Command Description devs Display a list of all devices known to the I/O system. It performs the same function as the kernel shell C interpreter command of the same name. 139 3 VxWorks Kernel Programmer's Guide, 6.6 Table 3-7 Command Provided with INCLUDE_BOOT_USB_FS_LOADER Command Description usbBulkShow nodeId Displays all the logical unit numbers of the USB device specified by nodeId (for example, a USB memory stick). It performs the same function as the kernel shell C interpreter command of the same name. For information about rebooting a system that is running VxWorks, see 3.6 Rebooting VxWorks, p.145. 3.5 Boot Loader Parameters The boot loader parameters include all the information needed to locate and load a VxWorks image, as well as other settings used to manage the boot process. As required by the specific boot configuration, they can include host and target IP addresses, the full path and name of the VxWorks image to be booted, the user name, and so on. Boot parameters can be changed interactively at runtime, or statically configured when the boot loader is created. Interactive changes to boot parameters are retained between reboots for most targets (in a non-volatile device or on disk). 3.5.1 Displaying Current Boot Parameters If the boot loader is configured with its command shell, the current set of boot loader parameters can be displayed interactively with the p command, as follows: [VxWorks Boot]: p A display similar to the following appears. Note that the p command does not actually display unassigned parameters, although this example shows them for completeness. boot device unit number processor number host name file name 140 : : : : : ln 0 0 mars c:\tmp\vxWorks 3 Boot Loader 3.5 Boot Loader Parameters inet on ethernet (e) : 90.0.0.50:ffffff00 inet on backplane (b) : host inet (h) : 90.0.0.1 gateway inet (g) : user (u) : fred ftp password (pw)(blank=use rsh) :secret flags (f) : 0x0 target name (tn) : phobos startup script (s) : other (o) : 3 This example corresponds to the configuration illustrated in Figure 3-1. Figure 3-1 Boot Configuration Example c:\temp\vxWorks HOST TARGET mars phobos user: fred 90.0.0.1 90.0.0.50:ffffff00 Ethernet 90.0.0.x subnet 3.5.2 Description of Boot Loader Parameters Each of the boot loader parameters is described below, with reference to the example shown above. The letters in parentheses after some of the parameters are alternative names used with the single-string interactive configuration method described in 3.5.3 Changing Boot Loader Parameters Interactively, p.144, and the static configuration method described in 3.7.3 Configuring Boot Loader Parameters Statically, p.147. boot device The type of device from which to boot. This must be one of the drivers included in the boot loader (for example, enp for a CMC controller). Due to limited space in boot media, only a few drivers can be included. A list of the drivers included in the boot loader image can be displayed in the boot loader 141 VxWorks Kernel Programmer's Guide, 6.6 shell with the devs or h command. For more information about boot devices, see 3.7.5 Selecting a Boot Device, p.148. unit number The unit number of the boot device, starting at zero. processor number A unique numerical target identifier for systems with multiple targets on a backplane. The backplane master must have its processor number set to zero. For boards not connected to a backplane, a value of zero is typically used but is not required. host name The name of the host machine to boot from. This is the name by which the host is known to VxWorks; it need not be the name used by the host itself. (The host name is mars in the example above.) file name The full path name of the VxWorks image to be booted (c:\myProj\vxWorks in the example). This path name is also reported to the host when you start a target server, so that it can locate the host-resident image of VxWorks. The path name is limited to a 160 byte string, including the null terminator. inet on ethernet (e) The Internet Protocol (IP) address of a target system Ethernet interface, as well as the subnet mask used for that interface. The address consists of the IP address, in dot decimal format, followed by a colon, followed by the mask in hex format (here, 90.0.0.50:ffffff00). inet on backplane (b) The Internet address of a target system with a backplane interface (blank in the example). host inet (h) The Internet address of the host to boot from (90.0.0.1 in the example). gateway inet (g) The Internet address of a gateway node for the target if the host is not on the same network as the target (blank in the example). user (u) The user ID used to access the host for the purpose of loading the VxWorks image file (which is fred in the example). The user must have host permission to read the VxWorks image file. 142 3 Boot Loader 3.5 Boot Loader Parameters On a Windows host, the user specified with this parameter must have FTP access to the host, and the ftp password parameter (below) must be used to provide the associated password. On a UNIX (Linux or Solaris) host, the user must have FTP, TFTP, or rsh access. For rsh, the user must be granted access by adding the user ID to the host's /etc/host.equiv file, or more typically to the user's .rhosts file (~userName/.rhosts). ftp password (pw) For FTP or TFTP access, this field is used for the password for the user identified with the user parameter (above). For rsh access it should be left blank. NOTE: If this parameter is not used, the boot loader attempts to load the run-time system image using a protocol based on the UNIX rsh utility, which is not available for Windows hosts. flags (f) Configuration options specified as a numeric value that is the sum of the values of selected option bits defined below. (This field is zero in the example because no special boot options were selected.) = Do not enable the system controller, even if the processor number is 0. (This option is board specific; refer to your target documentation.) 0x02 = Load all VxWorks symbolsa, instead of just globals. 0x04 = Do not auto-boot. 0x08 = Auto-boot fast (short countdown). 0x20 = Disable login security. 0x80 = Use TFTP to get boot image. 0x400 = Set system to debug mode for the error detection and reporting facility (depending on whether you are working on kernel modules or user applications, for more information see 11. Error Detection and Reporting. 0x01 a. Loading a very large group of symbol can cause delays of up to several minutes while Workbench loads the symbols. For information about how to specify the size of the symbol batch to load, see the Wind River Workbench User’s Guide. target name (tn) The name of the target system to be added to the host table (in the example, phobos). startup script (s) If the kernel shell is included in the downloaded image, this parameter allows you to pass to it the path and filename of a startup script to execute after the 143 3 VxWorks Kernel Programmer's Guide, 6.6 system boots. A startup script file can contain only the shell’s C interpreter commands. (Note that you must not add the INCLUDE_SHELL, INCLUDE_WDB_BANNER, or INCLUDE_SIMPLE_BANNER components to a boot loader. These components conflict with the boot loader shell. Doing so causes project configuration errors.) This parameter can also be used to specify process-based (RTP) applications to run automatically at boot time, if VxWorks has been configured with the appropriate components. See VxWorks Application Programmer’s Guide: Applications and Processes. other (o) This parameter is generally unused and available for applications (blank in the example). It can be used, for example, for specifying the default network interface when booting from a file system device. For more information, see 3.7.4 Enabling Networking for Non-Boot Interfaces, p.148. 3.5.3 Changing Boot Loader Parameters Interactively Boot parameters can be entered interactively from the boot loader prompt, either individually or as a string. NOTE: Interactively-defined boot parameters take precedence over statically-defined parameters for targets that store those changes. Most targets store interactively-defined boot settings in a non-volatile device (or a text file for Pentium BSPs), and do not use the statically-defined values for subsequent reboots. For information about changing boot parameters statically, see 3.7.3 Configuring Boot Loader Parameters Statically, p.147. Changing Parameters Individually To change parameters on an individual basis, first use the c (change) command at the boot prompt, and then enter a new value for each parameter as it is displayed. If a particular field already has the correct value, simply press ENTER. To clear a field, type a period (.), then press ENTER. To go back to change the previous parameter, type a dash (-), then press ENTER. If you want to quit before completing all parameters (but saving your changes), press CTRL+D. 144 3 Boot Loader 3.6 Rebooting VxWorks Changing Multiple Parameters Simultaneously To change more than one parameter at time, use the $ boot command at the boot prompt with a parameter string. The syntax is as follows: $dev(0,procnum)host:/file h=# e=# b=# g=# u=usr [pw=passwd] f=# tn=targetname s=script o=other For example: [VxWorks Boot]:$ln(0,0)mars:c:\myProj\vxWorks e=90.0.0.50 h=90.0.0.1 u=fred pw=… The order of the parameters with assignments (those with equal signs) is not important. Omit any assigned fields that are irrelevant. The codes for the assigned fields correspond to the letter codes shown in parentheses by the p command and in 3.5.2 Description of Boot Loader Parameters, p.141. This method can be particularly useful when booting a target from a host script. The changes made to boot parameters are retained between reboots for most types of targets (in a non-volatile device or on disk). 3.6 Rebooting VxWorks When VxWorks is running, any of the following means can be used to reboot it: ■ Enter CTRL+X in the terminal window. Note that some Windows terminal emulators do not pass CTRL+X to the target, because of its standard Windows meaning. ■ Invoke reboot( ) from the shell. ■ Press the reset button on the target system. ■ Turn the target’s power off and on. When you reboot VxWorks in any of these ways, the auto-boot sequence begins again from the countdown. 145 3 VxWorks Kernel Programmer's Guide, 6.6 3.7 Customizing and Building Boot Loaders A boot loader can be configured with just those VxWorks components that are required for a given system. Boot loaders may need to be customized and rebuilt for a variety of reasons, including the following: ■ The target is not on a network. ■ The boot loader must use a device or protocol that is not included in the default boot loader image. ■ An alternate boot method is preferable (such as booting over the Target Server File System). ■ To statically re-define the default boot loader parameters. When the default boot loader image is used with a system that does not have a non-volatile device or disk, the boot loader parameters have to be re-entered manually each time the target is rebooted. (Note that Pentium boot loaders automatically write boot parameter changes back to disk.) ■ To create boot loaders for production systems. In addition to setting the boot loader parameters appropriately, features that are not required (such as the network stack) can be removed to reduce the size of the boot loader image. 3.7.1 Configuring Boot Loaders For most BSPs, boot loaders can be configured and built with Wind River Workbench or the command-line project tool vxprj, using the PROFILE_BOOTAPP configuration profile. For some BSPs, the legacy method using bspDir/config.h and bspDir/make must be used. Note that the legacy method has been deprecated for most purposes, and cannot be used for multiprocessor development. For information about this method, see the VxWorks Command-Line Tools User’s Guide. 3.7.2 Boot Loader Components The INCLUDE_BOOT_APP component provides the basic facility for loading and executing a VxWorks image. The PROFILE_BOOTAPP configuration profile can be used with Workbench or vxprj to create a boot loader (including INCLUDE_BOOT_APP). This profile includes a basic set of boot loader components, such as those for the boot loader 146 3 Boot Loader 3.7 Customizing and Building Boot Loaders shell, drivers, file systems, and so on. Among the components that PROFILE_BOOTAPP provides are those for loading and executing a VxWorks image, for booting from a network with various protocols, and for booting from various file systems. A boot loader needs to be configured appropriately for any device or file system from which you want to boot. Other components, which can be used to create a boot loader for specific boot environments and with various boot management facilities, are described throughout this chapter. 3.7.3 Configuring Boot Loader Parameters Statically Boot loader parameters include the boot device, IP addresses of the host and target systems, the location of VxWorks image file, and so on. For detailed information about the parameters, see 3.5 Boot Loader Parameters, p.140. (For information about configuring boot loader parameters dynamically, see 3.5.3 Changing Boot Loader Parameters Interactively, p.144.) Using Workbench, the DEFAULT_BOOT_LINE configuration parameter of the INCLUDE_BSP_MACROS component can be used to change the default boot loader parameters. Using the legacy config.h method (which should only be used for BSPs that do not support PROFILE_BOOTAPP), edit the DEFAULT_BOOT_LINE macro in installDir/vxworks-6.x/target/config/bspName/config.h file to change the default boot loader parameters. The DEFAULT_BOOT_LINE macro for a Pentium BSP looks like the following: #define DEFAULT_BOOT_LINE \ "fd=0,0(0,0)host:/fd0/vxWorks.st h=90.0.0.3 e=90.0.0.50 u=target" For more information about configuration methods, see 3.7.1 Configuring Boot Loaders, p.146. NOTE: Interactively-defined boot parameters take precedence over statically-defined parameters for targets that store those changes. Most targets store interactively-defined boot settings in a non-volatile device (or a text file for Pentium BSPs), and do not use the statically-defined values for subsequent reboots. 147 3 VxWorks Kernel Programmer's Guide, 6.6 3.7.4 Enabling Networking for Non-Boot Interfaces The other (o) boot loader parameter can be used to specify a network interface in addition to whatever device is specified for the boot device. For example, it can be used when booting from a local SCSI disk to specify a network interface to be included. The following example illustrates parameter settings for booting from a SCSI device, and enabling the network with an on-board Ethernet device (here with ln for LANCE Ethernet device) with the other field. boot device processor number host name file name inet on ethernet (e) host inet (h) user (u) flags (f) target name (tn) other : : : : : : : : : : scsi=2,0 0 host /sd0/vxWorks 147.11.1.222:ffffff00 147.11.1.3 jane 0x0 t222 ln 3.7.5 Selecting a Boot Device The boot devices that are included in a boot loader image can be identified at run-time with the devs or h command from the boot loader shell (see 3.4.1 Boot Loader Shell Commands, p.136). Boot Device Configuration In order to boot VxWorks, however, the boot loader must be configured with the appropriate device or devices for your target hardware and desired boot options— they may not be provided by the default boot loader. The process of configuring the boot loader with devices is the same as for VxWorks itself, and the topic of device configuration is covered in 2.4.3 Device Driver Selection, p.22. Boot Device Specification Once a boot loader has been configured with the appropriate boot device (or devices), it must also be instructed as to which device to use. This can be done interactively or statically. For information about interactive specification using the boot device parameter, see 3.5.2 Description of Boot Loader Parameters, p.141 and 3.5.3 Changing Boot Loader Parameters Interactively, p.144. For information about static configuration, see 3.7.3 Configuring Boot Loader Parameters Statically, p.147. 148 3 Boot Loader 3.7 Customizing and Building Boot Loaders The boot devices that are supported by a given BSP are described in the BSP reference. The syntax used for specifying them with the boot device boot loader parameter is provided below. 3 ATA Device The syntax for specifying an ATA device is as follows: ata=controllerNum, driveNum where controllerNum is the controller number (either 0 or 1) and driveNum is the drive number (either 0 or 1). For example: ata=0,0 PCMCIA Device The syntax for specifying a PCMCIA device is as follows: pcmcia=socket where socket is the PCMCIA socket into which the device is plugged. SCSI Device The syntax for specifying a SCSI device is as follows: scsi=id,lun where id is the SCSI ID of the boot device, and lun is its Logical Unit Number (LUN). TSFS Device The syntax for specifying a Target Server File System device is simply tsfs. No additional boot device arguments are required. The file path and name must be relative to the root of the host file system as defined for the target server on the host. For information about the TSFS, see 8.9 Target Server File System: TSFS, p.518. 3.7.6 Reconfiguring Memory The VxWorks boot loader can be customized to meet the size constraints of the non-volatile device on a particular board, as well as the manner in which it retrieves the VxWorks image file. 149 VxWorks Kernel Programmer's Guide, 6.6 Persistent Memory Region The persistent memory region is an area of RAM at the top of system memory specifically reserved for error records and core dumps. For more information about use of persistent memory, see 11.2.2 Configuring the Persistent Memory Region, p.565. If you increase the size of the persistent memory region for VxWorks beyond the default, you must also create and install a new boot loader with the same PM_RESERVED_MEM value. If you do not, the boot loader (image plus heap) overlays the area of VxWorks persistent memory that extends beyond its own when the system reboots, and any data that may have been stored in the overlapping area will be corrupted. For a simple illustration of this problem, see Figure 3-2. Note that when you change the value of the PM_RESERVED_MEM for the boot loader, you need to change the value of RAM_HIGH_ADRS if there is insufficient room for the boot loader itself between RAM_HIGH_ADRS and sysMemTop( ). If you do so, also be sure that there is sufficient room for the VxWorks image between RAM_LOW_ADRS and RAM_HIGH_ADRS. ! WARNING: Not properly configuring the boot loader (as described above) could corrupt the persistent memory region when the system boots. 150 3 Boot Loader 3.7 Customizing and Building Boot Loaders Figure 3-2 RAM Layout Snapshots 3 Boot Loader Memory Layout VxWorks Memory Layout LOCAL_MEM_LOCAL_ADRS + LOCAL_MEM_SIZE Persistent Memory sysMemTop( ) Persistent Memory Boot Loader (image + heap) sysMemTop( ) RAM_HIGH_ADRS VxWorks (image + sys mem) VxWorks Image loaded here RAM_LOW_ADRS LOCAL_MEM_LOCAL_ADRS Area of VxWorks persistent memory overlayed by boot loader at reboot 3.7.7 Building Boot Loaders For boot loaders configured with Workbench or vxprj, and the PROFILE_BOOTAPP configuration profile, building them is the same as for any other VxWorks image project. If you have configured a boot loader with the bspDir/config.h method (which should only be used for BSPs that do not support PROFILE_BOOTAPP), use the command make bootLoaderType in the installDir/vxworks-6.x/target/config/bspName directory. For example: 151 VxWorks Kernel Programmer's Guide, 6.6 % make bootrom The different types of boot loader images that you can build are described in 3.3 Boot Loader Image Types, p.133. For information about configuration methods, see 3.7.1 Configuring Boot Loaders, p.146. ! CAUTION: Do not build boot loaders for symmetric multiprocessor (SMP) and asymmetric multiprocessor (AMP) configurations of VxWorks with the SMP or AMP build option—neither with Workbench nor with vxprj. The same boot loaders are used for uniprocessor (UP), SMP, and AMP, configurations of VxWorks. 3.8 Installing Boot Loaders For information about installing boot loaders in various media, see the VxWorks BSP references. 3.9 Booting From a Network In order to boot from a network, the boot loader must be configured with the appropriate components for the networking protocol and devices, and boot parameters must be set accordingly as well. For information about boot devices, see 3.7.5 Selecting a Boot Device, p.148. Network Protocol Components The ability to boot over a network is provided with the INCLUDE_BOOT_NETWORK component, which registers a network boot loader with the basic loader facility, checks for the network device, and calls the network boot loader for a specific protocol. Support for different protocols is as follows: 152 3 Boot Loader 3.9 Booting From a Network INCLUDE_BOOT_FTP_LOADER FTP boot loader. INCLUDE_BOOT_TFTP_LOADER TFTP boot loader. 3 INCLUDE_BOOT_RSH_LOADER RSH boot loader. Parameters for Booting From a Network The parameters and settings specific to booting from a network with a give protocol are described below. For general about boot parameters and how to set them, see 3.5.2 Description of Boot Loader Parameters, p.141, 3.5.3 Changing Boot Loader Parameters Interactively, p.144, and 3.7.3 Configuring Boot Loader Parameters Statically, p.147. FTP The user and ftp password boot parameters must be set to match account settings with the FTP server on the host. TFTP The flags boot parameter must be set to 0x80, and the user and ftp password parameters must be set match account settings with the TFTP server on the host. RSH The ftp password parameter must be set to empty, that is by entering . (a period). Updating Ethernet MAC Settings The INCLUDE_BOOT_ETH_MAC_HANDLER provides the M boot loader shell command, which can be used to update (and display) the Ethernet MAC address for the target system. For more information in this regard, see 3.4.1 Boot Loader Shell Commands, p.136. 153 VxWorks Kernel Programmer's Guide, 6.6 3.10 Booting From a Target File System In order to boot from a file system, the boot loader must be configured with the appropriate components and devices, and boot parameters must be set accordingly as well. For information about boot devices, see 3.7.5 Selecting a Boot Device, p.148. For information about booting from TSFS, see 3.11 Booting From the Host File System Using TSFS, p.155. File System Components The ability to boot from file systems is provided with the INCLUDE_BOOT_FILESYSTEMS component, in conjunction with a device-specific file system loader component. The options for file system loaders are as follows: INCLUDE_BOOT_ATA_LOADER Support for ATA devices. INCLUDE_BOOT_FD_LOADER Support for floppy-disk devices. Parameters for Booting From a Target File System The parameters specific to booting from a target file system are described below. For general about boot parameters and how to set them, see 3.5.2 Description of Boot Loader Parameters, p.141, 3.5.3 Changing Boot Loader Parameters Interactively, p.144, and 3.7.3 Configuring Boot Loader Parameters Statically, p.147. ATA The boot device boot loader parameter must be set to ata. FD—Floppy Disk The boot device boot loader parameter must be set to fd. 154 3 Boot Loader 3.11 Booting From the Host File System Using TSFS 3.11 Booting From the Host File System Using TSFS The simplest way to boot a target from a host without a network is to use the Target Server File System. This does not involve configuring SLIP or PPP. The TSFS can be used to boot a target connected to the host by one or two serial lines. Configure VxWorks with the INCLUDE_TSFS_BOOT component. ! WARNING: The TSFS boot facility is not compatible with WDB agent network configurations. For information about WDB, see 12.6 WDB Target Agent, p.626. To configure a boot loader for TSFS, the boot device parameter must be tsfs, and the file path and name must be relative to the root of the host file system defined for the target server. Regardless of how you specify the boot line parameters, you must reconfigure (as described below) and rebuild the boot image. If two serial lines connect the host and target (one for the target console and one for WDB communications), the following configuration parameters must be set: ■ ■ ■ ■ ■ ■ CONSOLE_TTY CONSOLE_TTY 0 WDB_TTY_CHANNEL WDB_TTY_CHANNEL 1 WDB_COMM_TYPE WDB_COMM_TYPE WDB_COMM_SERIAL If one serial line connects the host and target, the following configuration parameters must be set: ■ ■ ■ ■ ■ ■ CONSOLE_TTY CONSOLE_TTY NONE WDB_TTY_CHANNEL WDB_TTY_CHANNEL 0 WDB_COMM_TYPE WDB_COMM_TYPE WDB_COMM_SERIAL With any of these TSFS configurations, you can also use the target server console to set the boot loader parameters by including the INCLUDE_TSFS_BOOT_VIO_CONSOLE component in VxWorks. This disables the auto-boot mechanism, which might otherwise boot the target before the target server could start its virtual I/O mechanism. (The auto-boot mechanism is similarly disabled when CONSOLE_TTY is set to NONE, or when CONSOLE_TTY is set to WDB_TTY_CHANNEL.) Using the target server console is particularly useful 155 3 VxWorks Kernel Programmer's Guide, 6.6 for a single serial connection, as it provides an otherwise unavailable means of changing boot loader parameters from the command line. When you build the boot image, select bootrom.hex for the image type (see 3.7.7 Building Boot Loaders, p.151). For more information about the TSFS, see the 8.9 Target Server File System: TSFS, p.518. 156 4 Multitasking 4.1 Introduction 159 4.2 Tasks and Multitasking 160 4.3 Task Scheduling 166 4.4 Task Creation and Management 171 4.5 Task Error Status: errno 184 4.6 Task Exception Handling 187 4.7 Shared Code and Reentrancy 187 4.8 Intertask and Interprocess Communication 193 4.9 Public and Private Objects 194 4.10 Shared Data Structures 196 4.11 Mutual Exclusion 196 4.12 Semaphores 198 4.13 Message Queues 213 4.14 Pipes 218 4.15 VxWorks Events 219 4.16 Message Channels 226 4.17 Network Communication 226 4.18 Signals 226 157 VxWorks Kernel Programmer's Guide, 6.6 4.19 Watchdog Timers 239 4.20 Interrupt Service Routines 241 158 4 Multitasking 4.1 Introduction 4.1 Introduction Modern real-time systems are based on the complementary concepts of multitasking and intertask communications. A multitasking environment allows a real-time application to be constructed as a set of independent tasks, each with its own thread of execution and set of system resources. Tasks are the basic unit of scheduling in VxWorks. All tasks, whether in the kernel or in processes, are subject to the same scheduler. VxWorks processes are not themselves scheduled. Intertask communication facilities allow tasks to synchronize and communicate in order to coordinate their activity. In VxWorks, the intertask communication facilities include semaphores, message queues, message channels, pipes, network-transparent sockets, and signals. For interprocess communication, VxWorks semaphores and message queues, pipes, and events (as well as POSIX semaphores and events) can be created as public objects to provide accessibility across memory boundaries (between the kernel and processes, and between different processes). In addition, message channels provide a socket-based inter-processor and inter-process communications mechanism. Hardware interrupt handling is a key facility in real-time systems because interrupts are the usual mechanism to inform a system of external events. To get the fastest possible response to interrupts, interrupt service routines (ISRs) in VxWorks run in a special context of their own, outside any task’s context. VxWorks includes a watchdog-timer mechanism that allows any C function to be connected to a specified time delay. Watchdog timers are maintained as part of the system clock ISR. For information about POSIX timers, see 5.6 POSIX Clocks and Timers, p.259. This chapter discusses the tasking, intertask communication, and interprocess communication facilities that are at the heart of the VxWorks run-time environment. For information about POSIX support for VxWorks, see 5. POSIX Facilities. NOTE: This chapter provides information about facilities available in the VxWorks kernel. For information about facilities available to real-time processes, see the corresponding chapter in the VxWorks Application Programmer’s Guide. 159 4 VxWorks Kernel Programmer's Guide, 6.6 NOTE: This chapter provides information about multitasking facilities that are common to both uniprocessor (UP) and symmetric multiprocessor (SMP) configurations of VxWorks. It also provides information about those facilities that are specific to the UP configuration. In the latter case, the alternatives available for SMP systems are noted. With few exceptions, the symmetric multiprocessor (SMP) and uniprocessor (UP) configurations of VxWorks share the same API—the difference amounts to only a few routines. Also note that some programming practices—such as implicit synchronization techniques relying on task priority instead of explicit locking— are not appropriate for an SMP system. For information about SMP programming, see 15. VxWorks SMP. For information specifically about migration, see 15.15 Migrating Code to VxWorks SMP, p.702. 4.2 Tasks and Multitasking VxWorks tasks are the basic unit of code execution in the operating system itself, as well as in applications that it executes as processes. In other operating systems the term thread is used similarly. (For information about VxWorks support for POSIX threads, see 5.10 POSIX Threads, p.264). Multitasking provides the fundamental mechanism for an application to control and react to multiple, discrete real-world events. The VxWorks real-time kernel provides the basic multitasking environment. Multitasking creates the appearance of many threads of execution running concurrently when, in fact, the kernel interleaves their execution on the basis of a scheduling policy. Each task has its own context, which is the CPU environment and system resources that the task sees each time it is scheduled to run by the kernel. On a context switch, a task’s context is saved in the task control block (TCB). A task’s context includes: ■ a thread of execution; that is, the task’s program counter ■ the tasks’ virtual memory context (if process support is included) ■ the CPU registers and (optionally) coprocessor registers 160 4 Multitasking 4.2 Tasks and Multitasking ■ stacks for dynamic variables and function calls ■ I/O assignments for standard input, output, and error ■ a delay timer ■ a time-slice timer ■ kernel control structures ■ signal handlers ■ task private environment (for environment variables) ■ error status (errno) ■ debugging and performance monitoring values 4 If VxWorks is configured without process support (the INCLUDE_RTP component), the context of a task does not include its virtual memory context. All tasks can only run in a single common address space (the kernel). However, if VxWorks is configured with process support—regardless of whether or not any processes are active—the context of a kernel task does include its virtual memory context, because the system has the potential to operate with other virtual memory contexts besides the kernel. That is, the system could have tasks running in several different virtual memory contexts (the kernel and one or more processes). For information about virtual memory contexts, see 6. Memory Management. NOTE: The POSIX standard includes the concept of a thread, which is similar to a task, but with some additional features. For details, see 5.10 POSIX Threads, p.264. 4.2.1 Task States and Transitions The kernel maintains the current state of each task in the system. A task changes from one state to another as a result of kernel function calls made by the application. When created, tasks enter the suspended state. Activation is necessary for a created task to enter the ready state. The activation phase is extremely fast, enabling applications to pre-create tasks and activate them in a timely manner. An alternative is the spawning primitive, which allows a task to be created and activated with a single function. Tasks can be deleted from any state. 161 VxWorks Kernel Programmer's Guide, 6.6 Table 4-1 describes the state symbols that you see when working with development tools. Example 4-1 shows output from the i( ) command containing task state information. 162 4 Multitasking 4.2 Tasks and Multitasking Table 4-1 Task State Symbols State Symbol Description READY The task is not waiting for any resource other than the CPU. PEND The task is blocked due to the unavailability of some resource. DELAY The task is asleep for some duration. SUSPEND The task is unavailable for execution (but not pended or delayed). This state is used primarily for debugging. Suspension does not inhibit state transition, only execution. Thus, pended-suspended tasks can still unblock and delayed-suspended tasks can still awaken. STOP The task is stopped by the debugger. DELAY + S The task is both delayed and suspended. PEND + S The task is both pended and suspended. PEND + T The a task is pended with a timeout value. STOP + P Task is pended and stopped (by the debugger, error detection and reporting facilities, or SIGSTOP signal). STOP + S Task is stopped by (by the debugger, error detection and reporting facilities, or SIGSTOP signal) and suspended. STOP + T Task is delayed and stopped (by the debugger, error detection and reporting facilities, or SIGSTOP signal). PEND + S + T The task is pended with a timeout value and suspended. STOP +P + S Task is pended, suspended and stopped by the debugger. STOP + P + T Task pended with a timeout and stopped by the debugger. STOP +T + S Task is suspended, delayed, and stopped by the debugger. ST+P+S+T Task is pended with a timeout, suspended, and stopped by the debugger. state + I The task is specified by state (any state or combination of states listed above), plus an inherited priority. 163 4 VxWorks Kernel Programmer's Guide, 6.6 The STOP state is used by the debugger facilities when a breakpoint is hit. It is also used by the error detection and reporting facilities when an error condition occurs (see 11. Error Detection and Reporting). Example 4-1 Task States in Shell Command Output -> i NAME ---------tIsr0 tJobTask tExcTask tLogTask tNbioLog tShell0 tWdbTask tErfTask tXbdServic> tNet0 ipcom_sysl> ipnetd ipcom_teln> miiBusMoni> value = 0 = ENTRY TID PRI ------------ -------- --42cb40 25b1f74 0 3732d0 25b5140 0 372850 4f033c 0 logTask 25b7754 0 373f28 25bae18 0 shellTask 2fbdcb4 1 wdbTask 2faca28 3 42e0a0 25bd0a4 10 36e4b4 25ac3d0 50 ipcomNetTask 25cdb00 50 3cba50 27fec0c 50 3e2170 2fa6d10 50 ipcom_telnet 2fa979c 50 429420 25a8010 254 0x0 164 STATUS PC SP ERRNO DELAY ---------- -------- -------- ------- ----PEND 3bcf54 25b1f2c 0 0 PEND 3bcf54 25b50e8 0 0 PEND 3bcf54 4ef0f8 0 0 PEND 3bb757 25b7670 0 0 PEND 3bcf54 25bad6c 0 0 READY 3c2bdc 2fbc0d4 0 0 PEND 3bcf54 2fac974 0 0 PEND 3bd3be 25bd03c 0 0 PEND+T 3bd3be 25ac36c 3d0004 6 PEND 3bcf54 25cda88 0 0 PEND 3bd3be 27feab0 0 0 PEND 3bcf54 2fa6c98 3d0004 0 PEND 3bcf54 2fa9594 0 0 DELAY 3c162d 25a7fd0 0 93 4 Multitasking 4.2 Tasks and Multitasking Figure 4-1 illustrates task state transitions for a deployed system—without the STOP state associated with development activity. The routines listed are examples of ones that would cause the associated transition. For example, a task that called taskDelay( ) would move from the ready state to the delayed state. Figure 4-1 4 Task State Transitions The highest-priority ready task is executing. pended ready delayed suspended taskInit( ) ready ready ready pended pended delayed delayed suspended suspended suspended pended delayed suspended ready suspended ready suspended ready pended delayed semTake( ) / msgQReceive( ) taskDelay( ) taskSuspend( ) semGive( ) / msgQSend( ) taskSuspend( ) expired delay taskSuspend( ) taskResume( ) / taskActivate( ) taskResume( ) taskResume( ) 165 VxWorks Kernel Programmer's Guide, 6.6 4.3 Task Scheduling Multitasking requires a task scheduler to allocate the CPU to ready tasks. VxWorks provides the following scheduler options: ■ The traditional VxWorks scheduler, which provides priority-based, preemptive scheduling, as well as a round-robin extension. See 4.3.3 VxWorks Traditional Scheduler, p.168. ■ The VxWorks POSIX threads scheduler, which is designed (and required) for running pthreads in processes (RTPs). See 5.12 POSIX and VxWorks Scheduling, p.277.) ■ A custom scheduler framework, which allows you to develop your own scheduler. See 2.10 Custom Scheduler, p.118. 4.3.1 Task Priorities Task scheduling relies on a task’s priority. The VxWorks kernel provides 256 priority levels, numbered 0 through 255. Priority 0 is the highest and priority 255 is the lowest. A task is assigned its priority at creation, but you can also change it programmatically thereafter. For information about priority assignment, see 4.4.1 Task Creation and Activation, p.172 and 4.3.2 Task Scheduling Control, p.167). Application Task Priorities All application tasks should be in the priority range from 100 to 255. Driver Task Priorities In contrast to application tasks, which should be in the task priority range from 100 to 255, driver support tasks (which are associated with an ISR) can be in the range of 51-99. These tasks are crucial; for example, if a support task fails while copying data from a chip, the device loses that data. Examples of driver support tasks include tNet0 (the VxWorks network daemon task), an HDLC task, and so on. The system tNet0 has a priority of 50, so user tasks should not be assigned priorities below that task; if they are, the network connection could die and prevent debugging capabilities with the host tools. 166 4 Multitasking 4.3 Task Scheduling 4.3.2 Task Scheduling Control The routines that control task scheduling are listed in Table 4-2. Table 4-2 Task Scheduling Control Routines 4 Routine Description kernelTimeSlice( ) Controls round-robin scheduling. See Round-Robin Scheduling, p.169. taskRotate( ) Rotates tasks on the ready queue. taskPrioritySet( ) Changes the priority of a task. taskLock( ) Disables task rescheduling. taskUnlock( ) Enables task rescheduling. The taskRotate( )routine can be used as an alternative to round-robin scheduling. It allows a program to control sharing of the CPU amongst tasks of the same priority that are ready to run, rather than having the system do so at predetermined equal intervals. For information about round-robin scheduling, see Round-Robin Scheduling, p.169. Task Priority Tasks are assigned a priority when they are created (see 4.4.1 Task Creation and Activation, p.172). You can change a task’s priority level while it is executing by calling taskPrioritySet( ). The ability to change task priorities dynamically allows applications to track precedence changes in the real world. Preemption Locks The scheduler can be explicitly disabled and enabled on a per-task basis in the kernel with the routines taskLock( ) and taskUnlock( ). When a task disables the scheduler by calling taskLock( ), no priority-based preemption can take place while that task is running. If the task that has disabled the scheduler with taskLock( ) explicitly blocks or suspends, the scheduler selects the next highest-priority eligible task to execute. 167 VxWorks Kernel Programmer's Guide, 6.6 When the preemption-locked task unblocks and begins running again, preemption is again disabled. NOTE: The taskLock( ) and taskUnlock( ) routines are provided for the UP configuration of VxWorks, but not the SMP configuration. Several alternative are available for SMP systems, including task-only spinlocks, which default to taskLock( ) and taskUnlock( ) behavior in a UP system. For more information, see 15.6.2 Task-Only Spinlocks, p.682 and 15.15 Migrating Code to VxWorks SMP, p.702. Note that preemption locks prevent task context switching, but do not lock out interrupt handling. Preemption locks can be used to achieve mutual exclusion; however, keep the duration of preemption locking to a minimum. For more information, see 4.11 Mutual Exclusion, p.196. A Comparison of taskLock( ) and intLock( ) When using taskLock( ), consider that it will not achieve mutual exclusion. Generally, if interrupted by hardware, the system will eventually return to your task. However, if you block, you lose task lockout. Thus, before you return from the routine, taskUnlock( ) should be called. When a task is accessing a variable or data structure that is also accessed by an ISR, you can use intLock( ) to achieve mutual exclusion. Using intLock( ) makes the operation atomic in a single processor environment. It is best if the operation is kept minimal, meaning a few lines of code and no function calls. If the call is too long, it can directly impact interrupt latency and cause the system to become far less deterministic. For information about interrupts, see 4.11.1 Interrupt Locks and Latency, p.197 and 4.20 Interrupt Service Routines, p.241. 4.3.3 VxWorks Traditional Scheduler The VxWorks traditional scheduler provides priority-based preemptive scheduling as well as the option of programmatically initiating round-robin scheduling. The traditional scheduler may also be referred to as the original or native scheduler. The traditional scheduler is included in VxWorks by default with the INCLUDE_VX_TRADITIONAL_SCHEDULER component. 168 4 Multitasking 4.3 Task Scheduling For information about the POSIX thread scheduler and custom schedulers, see 5.12 POSIX and VxWorks Scheduling, p.277 and 2.10 Custom Scheduler, p.118, respectively. Priority-Based Preemptive Scheduling 4 A priority-based preemptive scheduler preempts the CPU when a task has a higher priority than the current task running. Thus, the kernel ensures that the CPU is always allocated to the highest priority task that is ready to run. This means that if a task—with a higher priority than that of the current task—becomes ready to run, the kernel immediately saves the current task’s context, and switches to the context of the higher priority task. For example, in Figure 4-2, task t1 is preempted by higher-priority task t2, which in turn is preempted by t3. When t3 completes, t2 continues executing. When t2 completes execution, t1 continues executing. The disadvantage of this scheduling policy is that, when multiple tasks of equal priority must share the processor, if a single task is never blocked, it can usurp the processor. Thus, other equal-priority tasks are never given a chance to run. Round-robin scheduling solves this problem. Figure 4-2 Priority Preemption t3 priority HIGH LOW t2 t2 t1 t1 time KEY: = preemption = task completion Round-Robin Scheduling VxWorks provides a round-robin extension to priority-based preemptive scheduling. Round-robin scheduling accommodates instances in which there are more than one task of a given priority that is ready to run. The round-robin 169 VxWorks Kernel Programmer's Guide, 6.6 algorithm attempts to share the CPU amongst these tasks by using time-slicing. Each task in a group of tasks with the same priority executes for a defined interval, or time slice, before relinquishing the CPU to the next task in the group. No one of them, therefore, can usurp the processor until it is blocked. See Figure 4-3 for an illustration of this activity. Note that while round-robin scheduling is used in some operating systems to provide equal CPU time to all tasks (or processes), regardless of their priority, this is not the case with VxWorks. Priority-based preemption is essentially unaffected by the VxWorks implementation of round-robin scheduling. Any higher-priority task that is ready to run immediately gets the CPU, regardless of whether or not the current task is done with its slice of execution time. When the interrupted task gets to run again, it simply continues using its unfinished execution time. In most systems, it is not necessary to enable round-robin scheduling, the exception being when multiple copies of the same code are to be run, such as in a user interface task. Note that the taskRotate( )routine can be used as an alternative to round-robin scheduling. It is useful for situations in which you want to share the CPU amongst tasks of the same priority that are ready to run, but to do so as a program requires, rather than at predetermined equal intervals. Enabling Round-Robin Scheduling Round-robin scheduling is enabled by calling kernelTimeSlice( ), which takes a parameter for a time slice, or interval. Time-slice Counts and Preemption The time-slice or interval defined with a kernelTimeSlice( ) call is the amount of time that each task is allowed to run before relinquishing the processor to another equal-priority task. Thus, the tasks rotate, each executing for an equal interval of time. No task gets a second slice of time before all other tasks in the priority group have been allowed to run. If round-robin scheduling is enabled, and preemption is enabled for the executing task, the system tick handler increments the task’s time-slice count. When the specified time-slice interval is completed, the system tick handler clears the counter and the task is placed at the tail of the list of tasks at its priority level. New tasks joining a given priority group are placed at the tail of the group with their run-time counter initialized to zero. Enabling round-robin scheduling does not affect the performance of task context switches, nor is additional memory allocated. 170 4 Multitasking 4.4 Task Creation and Management If a task blocks or is preempted by a higher priority task during its interval, its time-slice count is saved and then restored when the task becomes eligible for execution. In the case of preemption, the task will resume execution once the higher priority task completes, assuming that no other task of a higher priority is ready to run. In the case where the task blocks, it is placed at the tail of the list of tasks at its priority level. If preemption is disabled during round-robin scheduling, the time-slice count of the executing task is not incremented. Time-slice counts are accrued by the task that is executing when a system tick occurs, regardless of whether or not the task has executed for the entire tick interval. Due to preemption by higher priority tasks or ISRs stealing CPU time from the task, it is possible for a task to effectively execute for either more or less total CPU time than its allotted time slice. Figure 4-3 shows round-robin scheduling for three tasks of the same priority: t1, t2, and t3. Task t2 is preempted by a higher priority task t4 but resumes at the count where it left off when t4 is finished. Figure 4-3 Round-Robin Scheduling t4 HIGH priority time slice LOW t1 t2 t3 t1 t2 t2 t3 time KEY: = preemption = task completion 4.4 Task Creation and Management The following sections give an overview of the basic VxWorks task routines, which are found in the VxWorks library taskLib. These routines provide the means for 171 4 VxWorks Kernel Programmer's Guide, 6.6 task creation and control, as well as for retrieving information about tasks. See the VxWorks API reference for taskLib for further information. For interactive use, you can control VxWorks tasks with the host tools or the kernel shell; see the Wind River Workbench User’s Guide, the VxWorks Command-Line Tools User’s Guide, and VxWorks Kernel Programmer’s Guide: Target Tools. 4.4.1 Task Creation and Activation The routines listed in Table 4-3 are used to create tasks. The arguments to taskSpawn( ) are the new task’s name (an ASCII string), the task’s priority, an options word, the stack size, the main routine address, and 10 arguments to be passed to the main routine as startup parameters: id = taskSpawn ( name, priority, options, stacksize, main, arg1, …arg10 ); Note that a task’s priority can be changed after it has been spawned; see 4.3.2 Task Scheduling Control, p.167. The taskSpawn( ) routine creates the new task context, which includes allocating the stack and setting up the task environment to call the main routine (an ordinary subroutine) with the specified arguments. The new task begins execution at the entry to the specified routine. Table 4-3 Task Creation Routines Call Description taskSpawn( ) Spawns (creates and activates) a new task. taskCreate( ) Creates, but not activates a new task. taskInit( ) Initializes a new task. taskInitExcStk( ) Initializes a task with stacks at specified addresses. taskOpen( ) Open a task (or optionally create one, if it does not exist). taskActivate( ) Activates an initialized task. The taskOpen( ) routine provides a POSIX-like API for creating a task (with optional activation) or obtaining a handle on existing task. It also provides for creating a task as either a public or private object (see 4.4.4 Task Names and IDs, p.177). The taskOpen( ) routine is the most general purpose task-creation routine. 172 4 Multitasking 4.4 Task Creation and Management The taskSpawn( ) routine embodies the lower-level steps of allocation, initialization, and activation. The initialization and activation functions are provided by the routines taskCreate( ) and taskActivate( ); however, Wind River recommends that you use these routines only when you need greater control over allocation or activation. The difference between taskInit( ) and taskInitExcStk( ) is that the taskInit( ) routine allows the specification of the execution stack address, while taskInitExcStk( ) allows the specification of both the execution and exception stacks. 4.4.2 Task Creation Options When a task is spawned, you can pass in one or more option parameters, which are listed in Table 4-4. The result is determined by performing a logical OR operation on the specified options. 173 4 VxWorks Kernel Programmer's Guide, 6.6 Table 4-4 Task Options Name Description VX_ALTIVEC_TASK Execute with Altivec coprocessor support. VX_DEALLOC_EXC_STACK Deallocates the exception stack. VX_DEALLOC_STACK Deallocate stack. VX_DSP_TASK Execute with DSP coprocessor support. VX_FP_TASK Executes with the floating-point coprocessor. VX_NO_STACK_FILL Does not fill the stack with 0xEE. VX_NO_STACK_PROTECT Create without stack overflow or underflow guard zones (see 4.4.3 Task Stack, p.175). VX_PRIVATE_ENV Executes a task with a private environment. VX_TASK_NOACTIVATE Used with taskOpen( ) so that the task is not activated. VX_UNBREAKABLE Disables breakpoints for the task. Floating Point Operations You must include the VX_FP_TASK option when creating a task that does any of the following: ■ Performs floating-point operations. ■ Calls any function that returns a floating-point value. ■ Calls any function that takes a floating-point value as an argument. For example: tid = taskSpawn ("tMyTask", 90, VX_FP_TASK, 20000, myFunc, 2387, 0, 0, 0, 0, 0, 0, 0, 0, 0); Some routines perform floating-point operations internally. The VxWorks documentation for each of these routines clearly states the need to use the VX_FP_TASK option. 174 4 Multitasking 4.4 Task Creation and Management Filling Task Stacks Note that in addition to using the VX_NO_STACK_FILL task creation option for individual tasks, you can use the VX_GLOBAL_NO_STACK_FILL configuration parameter (when you configure VxWorks) to disable stack filling for all tasks and interrupts in the system. By default, task and interrupt stacks are filled with 0xEE. Filling stacks is useful during development for debugging with the checkStack( ) routine. It is generally not used in deployed systems because not filling stacks provides better performance during task creation (and at boot time for statically-initialized tasks). After a task is spawned, you can examine or alter task options by using the routines listed in Table 4-5. Currently, only the VX_UNBREAKABLE option can be altered. Table 4-5 Task Option Routines Call Description taskOptionsGet( ) Examines task options. taskOptionsSet( ) Sets task options. 4.4.3 Task Stack The size of each task’s stack is defined when the task is created (see 4.4.1 Task Creation and Activation, p.172). It can be difficult, however, to know exactly how much stack space to allocate. To help avoid stack overflow and corruption, you can initially allocated a stack that is much larger than you expect the task to require. Then monitor the stack periodically from the shell with checkStack( ) or ti( ). When you have determined actual usage, adjust the stack size accordingly for testing and for the deployed system. In addition to experimenting with task stack size, you can also configure and test systems with guard zone protection for task stacks (for more information, see Task Stack Protection, p.176). 175 4 VxWorks Kernel Programmer's Guide, 6.6 Task Stack Protection Task stacks can be protected with guard zones and by making task stacks non-executable. Task Stack Guard Zones Systems can be configured with the INCLUDE_PROTECT_TASK_STACK component to provide guard zone protection for task stacks. If memory usage becomes an issue, the component can be removed for final testing and the deployed system. An overrun guard zone prevents a task from going beyond the end of its predefined stack size and corrupting data or other stacks. An under-run guard zone typically prevents buffer overflows from corrupting memory that precedes the base of the stack. The CPU generates an exception when a task attempts to access any of the guard zones. The size of a stack is always rounded up to a multiple of the MMU page size when either a guard zone is inserted or when the stack is made non-executable. Note that guard zones cannot catch instances in which a buffer that causes an overflow is greater than the page size (although this is rare). For example, if the guard zone is one page of 4096 bytes, and the stack is near its end, and then a buffer of a 8000 bytes is allocated on the stack, the overflow will not be detected. By default, kernel mode tasks do not have any task stack protection. Configuring VxWorks with the INCLUDE_PROTECT_TASK_STACK component provides underflow and overflow guard zones on the execution stacks, but none for the exception stacks. Stack guard zones in the kernel are mapped to physical memory. Note that the protection provided for user-mode tasks by configuring the system with the INCLUDE_RTP component does not apply to kernel tasks (for information about user-mode task stack protection, see the VxWorks Application Programmer’s Guide: Multitasking). Note that the INCLUDE_PROTECT_TASK_STACK component does not provide stack protection for tasks that are created with the VX_NO_STACK_PROTECT task option (see 4.4.2 Task Creation Options, p.173). If a task is created with this option, no guard zones are created for that task. The size of the guard zones are defined by the following configuration parameters: ■ TASK_KERNEL_EXEC_STACK_OVERFLOW_SIZE for kernel task execution stack overflow size. 176 4 Multitasking 4.4 Task Creation and Management ■ TASK_KERNEL_EXEC_STACK_UNDERFLOW_SIZE for kernel task execution stack underflow size. The value of these parameters can be modified to increase the size of the guard zones on a system-wide basis. The size of a guard zone is rounded up to a multiple of the CPU MMU page size. The insertion of a guard zone can be prevented by setting the parameter to zero. Stack guard zones in the kernel consume RAM, as guard zones correspond to mapped memory for which accesses are made invalid. Non-Executable Task Stacks VxWorks creates kernel task stacks with a non-executable attribute only if the system is configured with the INCLUDE_TASK_STACK_NO_EXEC component, and if the CPU supports making memory non-executable on an MMU-page basis. The size of a stack is always rounded up to a multiple of an MMU page size when the stack is made non-executable (as is also the case when guard zones are inserted). 4.4.4 Task Names and IDs When a task is spawned, you can specify an ASCII string of any length to be the task name, and a task ID is returned. Most VxWorks task routines take a task ID as the argument specifying a task. VxWorks uses a convention that a task ID of 0 (zero) always implies the calling task. In the kernel, the task ID is a 4-byte handle to the task’s data structures. The following rules and guidelines should be followed when naming tasks: ■ The names of public tasks must be unique and must begin with a forward slash; for example /tMyTask. Note that public tasks are visible throughout the entire system—in the kernel and any processes. ■ The names of private tasks should be unique. VxWorks does not require that private task names be unique, but it is preferable to use unique names to avoid confusing the user. (Note that private tasks are visible only within the entity in which they were created—either the kernel or a process.) To use the host development tools to their best advantage, task names should not conflict with globally visible routine or variable names. To avoid name conflicts, VxWorks uses a convention of prefixing any kernel task name started from the target with the letter t, and any task name started from the host with the letter u. In addition, the name of the initial task of a real-time process is the executable file name (less the extension) prefixed with the letter i. 177 4 VxWorks Kernel Programmer's Guide, 6.6 Creating a task as a public object allows other tasks from outside of its process to send signals or events to it (with the taskKill( ) or the eventSend( ) routine, respectively). For more information, see 4.9 Public and Private Objects, p.194. You do not have to explicitly name tasks. If a NULL pointer is supplied for the name argument of taskSpawn( ), then VxWorks assigns a unique name. The name is of the form tN, where N is a decimal integer that is incremented by one for each unnamed task that is spawned. The taskLib routines listed in Table 4-6 manage task IDs and names. Table 4-6 Task Name and ID Routines Call Description taskName( ) Gets the task name associated with a task ID (restricted to the context—process or kernel—in which it is called). taskNameToId( ) Looks up the task ID associated with a task name. taskIdSelf( ) Gets the calling task’s ID. taskIdVerify( ) Verifies the existence of a specified task. 178 4 Multitasking 4.4 Task Creation and Management 4.4.5 Task Information The routines listed in Table 4-7 get information about a task by taking a snapshot of a task’s context when the routine is called. Because the task state is dynamic, the information may not be current unless the task is known to be dormant (that is, suspended). Table 4-7 Task Information Routines Call Description taskIdListGet( ) Fills an array with the IDs of all active tasks. taskInfoGet( ) Gets information about a task. taskPriorityGet( ) Examines the priority of a task. taskRegsGet( ) Examines a task’s registers (cannot use with current task). taskRegsSet( ) Sets a task’s registers (cannot be used with the current task). taskIsSuspended( ) Checks whether a task is suspended. taskIsReady( ) Checks whether a task is ready to run. taskIsPended( ) Checks whether a task is pended. taskTcb( ) Gets a pointer to a task’s control block. For information about task-specific variables and their use, see 4.7.3 Task-Specific Variables, p.190. 179 4 VxWorks Kernel Programmer's Guide, 6.6 4.4.6 Task Deletion and Deletion Safety Tasks can be dynamically deleted from the system. VxWorks includes the routines listed in Table 4-8 to delete tasks and to protect tasks from unexpected deletion. Table 4-8 Task-Deletion Routines Call Description exit( ) Terminates the calling task and frees memory (task stacks and task control blocks only).a taskDelete( ) Terminates a specified task and frees memory (task stacks and task control blocks only).a The calling task may terminate itself with this routine. taskSafe( ) Protects the calling task from deletion. taskUnsafe( ) Undoes a taskSafe( ), which makes calling task available for deletion. a. Memory that is allocated by the task during its execution is not freed when the task is terminated. ! WARNING: Make sure that tasks are not deleted at inappropriate times. Before an application deletes a task, the task should release all shared resources that it holds. Tasks implicitly call exit( ) if the entry routine specified during task creation returns. When a task is deleted, no other task is notified of this deletion. The routines taskSafe( ) and taskUnsafe( ) address problems that stem from unexpected deletion of tasks. The routine taskSafe( ) protects a task from deletion by other tasks. This protection is often needed when a task executes in a critical region or engages a critical resource. For example, a task might take a semaphore for exclusive access to some data structure. While executing inside the critical region, the task might be deleted by another task. Because the task is unable to complete the critical region, the data structure might be left in a corrupt or inconsistent state. Furthermore, because the semaphore can never be released by the task, the critical resource is now unavailable for use by any other task and is essentially frozen. Using taskSafe( ) to protect the task that took the semaphore prevents such an outcome. Any task that tries to delete a task protected with taskSafe( ) is blocked. 180 4 Multitasking 4.4 Task Creation and Management When finished with its critical resource, the protected task can make itself available for deletion by calling taskUnsafe( ), which readies any deleting task. To support nested deletion-safe regions, a count is kept of the number of times taskSafe( ) and taskUnsafe( ) are called. Deletion is allowed only when the count is zero, that is, there are as many unsafes as safes. Only the calling task is protected. A task cannot make another task safe or unsafe from deletion. The following code fragment shows how to use taskSafe( ) and taskUnsafe( ) to protect a critical region of code: taskSafe (); semTake (semId, WAIT_FOREVER); . . /* critical region code */ . semGive (semId); taskUnsafe (); /* Block until semaphore available */ /* Release semaphore */ Deletion safety is often coupled closely with mutual exclusion, as in this example. For convenience and efficiency, a special kind of semaphore, the mutual-exclusion semaphore, offers an option for deletion safety. For more information, see 4.12.3 Mutual-Exclusion Semaphores, p.205. 4.4.7 Task Execution Control The routines listed in Table 4-9 provide direct control over a task’s execution. Table 4-9 Task Execution Control Routines Call Description taskSuspend( ) Suspends a task. taskResume( ) Resumes a task. taskRestart( ) Restarts a task. taskDelay( ) Delays a task; delay units are ticks, resolution in ticks. nanosleep( ) Delays a task; delay units are nanoseconds, resolution in ticks. Tasks may require restarting during execution in response to some catastrophic error. The restart mechanism, taskRestart( ), recreates a task with the original creation arguments. 181 4 VxWorks Kernel Programmer's Guide, 6.6 Delay operations provide a simple mechanism for a task to sleep for a fixed duration. Task delays are often used for polling applications. For example, to delay a task for half a second without making assumptions about the clock rate, call: taskDelay (sysClkRateGet ( ) / 2); The routine sysClkRateGet( ) returns the speed of the system clock in ticks per second. Instead of taskDelay( ), you can use the POSIX routine nanosleep( ) to specify a delay directly in time units. Only the units are different; the resolution of both delay routines is the same, and depends on the system clock. For details, see 5.6 POSIX Clocks and Timers, p.259. As a side effect, taskDelay( ) moves the calling task to the end of the ready queue for tasks of the same priority. In particular, you can yield the CPU to any other tasks of the same priority by delaying for zero clock ticks: taskDelay (NO_WAIT); /* allow other tasks of same priority to run */ A delay of zero duration is only possible with taskDelay( ); nanosleep( ) considers it an error. NOTE: ANSI and POSIX APIs are similar. System clock resolution is typically 60Hz (60 times per second). This is a relatively long time for one clock tick, and would be even at 100Hz or 120Hz. Thus, since periodic delaying is effectively polling, you may want to consider using event-driven techniques as an alternative. 4.4.8 Tasking Extensions To allow additional task-related facilities to be added to the system, VxWorks provides hook routines that allow additional routines to be invoked whenever a task is created, a task context switch occurs, or a task is deleted. There are spare fields in the task control block (TCB) available for application extension of a task’s context These hook routines are listed in Table 4-10; for more information, see the VxWorks API reference for taskHookLib. 182 4 Multitasking 4.4 Task Creation and Management Table 4-10 Task Create, Switch, and Delete Hooks Call Description taskCreateHookAdd( ) Adds a routine to be called at every task create. taskCreateHookDelete( ) Deletes a previously added task create routine. taskSwitchHookAdd( ) Adds a routine to be called at every task switch. taskSwitchHookDelete( ) Deletes a previously added task switch routine. taskDeleteHookAdd( ) Adds a routine to be called at every task delete. taskDeleteHookDelete( ) Deletes a previously added task delete routine. When using switch hook routines, be aware of the following restrictions: ■ Do not assume any virtual memory (VM) context is current other than the kernel context (as with ISRs). ■ Do not rely on knowledge of the current task or invoke any function that relies on this information, for example taskIdSelf( ). ■ Do not rely on taskIdVerify (pOldTcb) to determine if a delete hook has executed for the self-destructing task case. Instead, other state information must be changed in the delete hook to be detected by the switch hook (for example by setting a pointer to NULL). Task create hook routines execute in the context of the creator task. Task create hooks must consider the ownership of any kernel objects (such as watchdog timers, semaphores, and so on) created in the hook routine. Since create hook routines execute in the context of the creator task, new kernel objects will be owned by the creator task's process. It may be necessary to assign the ownership of these objects to the new task's process. This will prevent unexpected object reclamation from occurring if and when the process of the creator task terminates. When the creator task is a kernel task, the kernel will own any kernel objects that are created. Thus there is no concern about unexpected object reclamation for this case. User-installed switch hooks are called within the kernel context and therefore do not have access to all VxWorks facilities. Table 4-11 summarizes the routines that can be called from a task switch hook; in general, any routine that does not involve the kernel can be called. 183 4 VxWorks Kernel Programmer's Guide, 6.6 Table 4-11 Routines Callable by Task Switch Hooks Library Routines bLib All routines fppArchLib fppSave( ), fppRestore( ) intLib intContext( ), intCount( ), intVecSet( ), intVecGet( ), intLock( ), intUnlock( ) lstLib All routines except lstFree( ) mathALib All are callable if fppSave( )/fppRestore( ) are used rngLib All routines except rngCreate( ) taskLib taskIdVerify( ), taskIdDefault( ), taskIsReady( ), taskIsSuspended( ), taskTcb( ) vxLib vxTas( ) NOTE: For information about POSIX extensions, see 5. POSIX Facilities. 4.5 Task Error Status: errno By convention, C library functions set a single global integer variable errno to an appropriate error number whenever the function encounters an error. This convention is specified as part of the ANSI C standard. NOTE: This section describes the implementation and use of errno in UP configurations of VxWorks, which is different from that in SMP configurations.For information about errno and other global variables in VxWorks SMP, see 15.15.8 SMP CPU-Specific Variables and Uniprocessor Global Variables, p.712. For information about migration, see 15.15 Migrating Code to VxWorks SMP, p.702. 184 4 Multitasking 4.5 Task Error Status: errno 4.5.1 Layered Definitions of errno In VxWorks, errno is simultaneously defined in two different ways. There is, as in ANSI C, an underlying global variable called errno, which you can display by name using host development tools. However, errno is also defined as a macro in errno.h; this is the definition visible to all of VxWorks except for one function. The macro is defined as a call to a function __errno( )that returns the address of the global variable, errno (as you might guess, this is the single function that does not itself use the macro definition for errno). This subterfuge yields a useful feature: because __errno( )is a function, you can place breakpoints on it while debugging, to determine where a particular error occurs. Nevertheless, because the result of the macro errno is the address of the global variable errno, C programs can set the value of errno in the standard way: errno = someErrorNumber; As with any other errno implementation, take care not to have a local variable of the same name. 4.5.2 A Separate errno Value for Each Task In VxWorks, the underlying global errno is a single predefined global variable that can be referenced directly by application code that is linked with VxWorks (either statically on the host or dynamically at load time). However, for errno to be useful in the multitasking environment of VxWorks, each task must see its own version of errno. Therefore errno is saved and restored by the kernel as part of each task’s context every time a context switch occurs. Similarly, interrupt service routines (ISRs) see their own versions of errno. This is accomplished by saving and restoring errno on the interrupt stack as part of the interrupt enter and exit code provided automatically by the kernel (see 4.20.1 Connecting Routines to Interrupts, p.242). Thus, regardless of the VxWorks context, an error code can be stored or consulted without direct manipulation of the global variable errno. 185 4 VxWorks Kernel Programmer's Guide, 6.6 4.5.3 Error Return Convention Almost all VxWorks functions follow a convention that indicates simple success or failure of their operation by the actual return value of the function. Many functions return only the status values OK (0) or ERROR (-1). Some functions that normally return a nonnegative number (for example, open( ) returns a file descriptor) also return ERROR to indicate an error. Functions that return a pointer usually return NULL (0) to indicate an error. In most cases, a function returning such an error indication also sets errno to the specific error code. The global variable errno is never cleared by VxWorks routines. Thus, its value always indicates the last error status set. When a VxWorks subroutine gets an error indication from a call to another routine, it usually returns its own error indication without modifying errno. Thus, the value of errno that is set in the lower-level routine remains available as the indication of error type. For example, the VxWorks routine intConnect( ), which connects a user routine to a hardware interrupt, allocates memory by calling malloc( ) and builds the interrupt driver in this allocated memory. If malloc( ) fails because insufficient memory remains in the pool, it sets errno to a code indicating an insufficient-memory error was encountered in the memory allocation library, memLib. The malloc( ) routine then returns NULL to indicate the failure. The intConnect( ) routine, receiving the NULL from malloc( ), then returns its own error indication of ERROR. However, it does not alter errno leaving it at the insufficient memory code set by malloc( ). For example: if ((pNew = malloc (CHUNK_SIZE)) = = NULL) return (ERROR); It is recommended that you use this mechanism in your own subroutines, setting and examining errno as a debugging technique. A string constant associated with errno can be displayed using printErrno( ) if the errno value has a corresponding string entered in the error-status symbol table, statSymTbl. See the VxWorks API reference for errnoLib for details on error-status values and building statSymTbl. 4.5.4 Assignment of Error Status Values VxWorks errno values encode the module that issues the error, in the most significant two bytes, and uses the least significant two bytes for individual error numbers. All VxWorks module numbers are in the range 1–500; errno values with a module number of zero are used for source compatibility. All other errno values (that is, positive values greater than or equal to 501<<16, and all negative values) are available for application use. 186 4 Multitasking 4.6 Task Exception Handling See the VxWorks API reference on errnoLib for more information about defining and decoding errno values with this convention. 4 4.6 Task Exception Handling Errors in program code or data can cause hardware exception conditions such as illegal instructions, bus or address errors, divide by zero, and so forth. The VxWorks exception handling package takes care of all such exceptions (see 11. Error Detection and Reporting). Tasks can also attach their own handlers for certain hardware exceptions through the signal facility. If a task has supplied a signal handler for an exception, the default exception handling described above is not performed. A user-defined signal handler is useful for recovering from catastrophic events. Typically, setjmp( ) is called to define the point in the program where control will be restored, and longjmp( ) is called in the signal handler to restore that context. Note that longjmp( ) restores the state of the task’s signal mask. Signals are also used for signaling software exceptions as well as hardware exceptions. They are described in more detail in 4.18 Signals, p.226 and in the VxWorks API reference for sigLib. 4.7 Shared Code and Reentrancy In VxWorks, it is common for a single copy of a subroutine or subroutine library to be invoked by many different tasks. For example, many tasks may call printf( ), but there is only a single copy of the subroutine in the system. A single copy of code executed by multiple tasks is called shared code. VxWorks dynamic linking facilities make this especially easy. Shared code makes a system more efficient and easier to maintain; see Figure 4-4. 187 VxWorks Kernel Programmer's Guide, 6.6 Figure 4-4 Shared Code TASKS taskOne (void) { myFunc(); ... } taskTwo (void) { myFunc(); ... } SHARED CODE myFunc (void) { ... } Shared code must be reentrant. A subroutine is reentrant if a single copy of the routine can be called from several task contexts simultaneously without conflict. Such conflict typically occurs when a subroutine modifies global or static variables, because there is only a single copy of the data and code. A routine’s references to such variables can overlap and interfere in invocations from different task contexts. Most routines in VxWorks are reentrant. However, you should assume that any routine someName( ) is not reentrant if there is a corresponding routine named someName_r( ) — the latter is provided as a reentrant version of the routine. For example, because ldiv( ) has a corresponding routine ldiv_r( ), you can assume that ldiv( ) is not reentrant. VxWorks I/O and driver routines are reentrant, but require careful application design. For buffered I/O, Wind River recommends using file-pointer buffers on a per-task basis. At the driver level, it is possible to load buffers with streams from different tasks, due to the global file descriptor table in VxWorks. This may or may not be desirable, depending on the nature of the application. For example, a packet driver can mix streams from different tasks because the packet header identifies the destination of each packet. The majority of VxWorks routines use the following reentrancy techniques: – – – dynamic stack variables global and static variables guarded by semaphores task variables Wind River recommends applying these same techniques when writing application code that can be called from several task contexts simultaneously. 188 4 Multitasking 4.7 Shared Code and Reentrancy NOTE: In some cases reentrant code is not preferable. A critical section should use a binary semaphore to guard it, or use intLock( ) or intUnlock( ) if called from by an ISR. NOTE: Initialization routines should be callable multiple times, even if logically they should only be called once. As a rule, routines should avoid static variables that keep state information. Initialization routines are an exception; using a static variable that returns the success or failure of the original initialization routine call is appropriate. 4.7.1 Dynamic Stack Variables Many subroutines are pure code, having no data of their own except dynamic stack variables. They work exclusively on data provided by the caller as parameters. The linked-list library, lstLib, is a good example of this. Its routines operate on lists and nodes provided by the caller in each subroutine call. Subroutines of this kind are inherently reentrant. Multiple tasks can use such routines simultaneously, without interfering with each other, because each task does indeed have its own stack. See Figure 4-5. Figure 4-5 Stack Variables and Shared Code TASKS taskOne ( ) { ... comFunc(1); ... } taskTwo ( ) { ... comFunc(2); ... } TASK STACKS COMMON SUBROUTINE ... var = 1 ... ... var = 2 ... comFunc (arg) { int var = arg; } 189 4 VxWorks Kernel Programmer's Guide, 6.6 4.7.2 Guarded Global and Static Variables Some libraries encapsulate access to common data. This kind of library requires some caution because the routines are not inherently reentrant. Multiple tasks simultaneously invoking the routines in the library might interfere with access to common variables. Such libraries must be made explicitly reentrant by providing a mutual-exclusion mechanism to prohibit tasks from simultaneously executing critical sections of code. The usual mutual-exclusion mechanism is the mutex semaphore facility provided by semMLib and described in 4.12.3 Mutual-Exclusion Semaphores, p.205. 4.7.3 Task-Specific Variables Task-specific variables can be used to ensure that shared code is reentrant by providing task-specific variables of the same name that are located in each task’s stack, instead of a standard global or static variables. Each task thereby has its own unique copy of the data item.This allows, for example, several tasks to reference a private buffer of memory and while referring to it with the same global variable name. NOTE: The __thread storage class variables can be used for both UP and SMP configurations of VxWorks, and Wind River recommends its use in both cases as the best method of providing task-specific variables. The taskVarLib and tlsOldLib (formerly tlsLib) facilities—for the kernel-space and user-space respectively— are maintained primarily for backwards-compatibility, are not compatible with VxWorks SMP, and their use is not recommended. In addition to being incompatible with VxWorks SMP, the taskVarLib and tlsOldLib facilities increase task context switch times. For information about migration, see 15.15 Migrating Code to VxWorks SMP, p.702. Also note that each task has a VxWorks events register, which receives events sent from other tasks, ISRs, semaphores, or message queues. See 4.15 VxWorks Events, p.219 for more information about this register, and the routines used to interact with it. Thread-Local Variables: __thread Storage Class Thread-local storage is a compiler facility that allows for allocation of a variable such that there are unique instances of the variable for each thread (or task, in VxWorks terms). 190 4 Multitasking 4.7 Shared Code and Reentrancy The __thread storage class instructs the compiler to make the defined variable a thread-local variable. This means one instance of the variable is created for every task in the system. The compiler key word is used as follows: __thread int i; 4 extern __thread struct state s; static __thread char *p; The __thread specifier may be used alone, with the extern or static specifiers, but with no other storage class specifier. When used with extern or static, __thread must appear immediately after the other storage class specifier. The __thread specifier may be applied to any global, file-scoped static, function-scoped static, or static data member of a class. It may not be applied to block-scoped automatic or non-static data member. When the address-of operator is applied to a thread-local variable, it is evaluated at run-time and returns the address of the current task’s instance of that variable. The address may be used by any task. When a task terminates, any pointers to thread-local variables in that task become invalid. No static initialization may refer to the address of a thread-local variable. In C++, if an initializer is present for a thread-local variable, it must be a constant-expression, as defined in 5.19.2 of the ANSI/ISO C++ standard. taskVarLib and Task Variables VxWorks provides a task variable facility (with taskVarLib) that allows 4-byte variables to be added to a task’s context, so that the value of such a variable is switched every time a task switch occurs to or from its owner task. NOTE: Wind River does not recommend using the taskVarLib facility, which is maintained primarily for backwards-compatibility. Use thread-local (__thread) storage class variables instead. 191 VxWorks Kernel Programmer's Guide, 6.6 4.7.4 Multiple Tasks with the Same Main Routine With VxWorks, it is possible to spawn several tasks with the same main routine. Each spawn creates a new task with its own stack and context. Each spawn can also pass the main routine different parameters to the new task. In this case, the same rules of reentrancy described in 4.7.3 Task-Specific Variables, p.190 apply to the entire task. This is useful when the same function must be performed concurrently with different sets of parameters. For example, a routine that monitors a particular kind of equipment might be spawned several times to monitor several different pieces of that equipment. The arguments to the main routine could indicate which particular piece of equipment the task is to monitor. In Figure 4-6, multiple joints of the mechanical arm use the same code. The tasks manipulating the joints invoke joint( ). The joint number (jointNum) is used to indicate which joint on the arm to manipulate. Figure 4-6 Multiple Tasks Utilizing Same Code joint_2 joint_3 joint_1 joint ( int jointNum ) { /* joint code here */ } 192 4 Multitasking 4.8 Intertask and Interprocess Communication 4.8 Intertask and Interprocess Communication The complement to the multitasking routines described in 4.2 Tasks and Multitasking, p.160 is the intertask communication facilities. These facilities permit independent tasks to coordinate their actions. VxWorks supplies a rich set of intertask and interprocess communication mechanisms, including: ■ Shared memory, for simple sharing of data. ■ Semaphores, for basic mutual exclusion and synchronization. ■ Mutexes and condition variables for mutual exclusion and synchronization using POSIX interfaces. ■ Message queues and pipes, for intertask message passing within a CPU. ■ VxWorks events, for communication and synchronization. ■ Message channels, for socket-based inter-processor and interprocess communication. ■ Sockets and remote procedure calls, for network-transparent intertask communication. Signals, for exception handling, interprocess communication, and process management. ■ NOTE: With few exceptions, the symmetric multiprocessor (SMP) and uniprocessor (UP) configurations of VxWorks share the same facilities for intertask and interprocess communications—the difference amounts to only a few routines. This section provides information about the APIs that are common to both configurations, as well as those APIs that are specific to the UP configuration. In the latter case, the alternatives available for SMP systems are noted. For information about the SMP configuration of VxWorks, see 15. VxWorks SMP; and for information specifically about migration, see 15.15 Migrating Code to VxWorks SMP, p.702. In addition, the VxMP component provides for intertask communication between multiple CPUs that share memory. See 16. Shared-Memory Objects: VxMP. 193 4 VxWorks Kernel Programmer's Guide, 6.6 4.9 Public and Private Objects Kernel objects such as semaphores and message queues can be created as either private or public objects. This provides control over the scope of their accessibility—which can be limited to a virtual memory context by defining them as private, or extended to the entire system (the kernel and any processes) by defining them as public. There is no difference in performance between a public and a private object. An object can only be defined as public or private when it is created—the designation cannot be changed thereafter. Public objects must be named when they are created, and the name must begin with a forward slash; for example, /foo. Private objects do not need to be named. For information about naming tasks in addition to that provided in this section, see 4.4.4 Task Names and IDs, p.177. 4.9.1 Creating and Naming Public and Private Objects Public objects are always named, and the name must begin with a forward-slash. Private objects can be named or unnamed. If they are named, the name must not begin with a forward-slash. Only one public object of a given class and name can be created. That is, there can be only one public semaphore with the name /foo. But there may be a public semaphore named /foo and a public message queue named /foo. Obviously, more distinctive naming is preferable (such as /fooSem and /fooMQ). The system allows creation of only one private object of a given class and name in any given memory context; that is, in any given process or in the kernel. For example: ■ If process A has created a private semaphore named bar, it cannot create a second semaphore named bar. ■ However, process B could create a private semaphore named bar, as long as it did not already own one with that same name. Note that private tasks are an exception to this rule—duplicate names are permitted for private tasks; see 4.4.4 Task Names and IDs, p.177. To create a named object, the appropriate xyzOpen( ) API must be used, such as semOpen( ). When the routine specifies a name that starts with a forward slash, the object will be public. 194 4 Multitasking 4.9 Public and Private Objects To delete public objects, the xyzDelete( ) API cannot be used (it can only be used with private objects). Instead, the xyzClose( ) and xyzUnlink( ) APIs must be used in accordance with the POSIX standard. That is, they must be unlinked from the name space, and then the last close operation will delete the object (for example, using the semUnlink( ) and semClose( ) APIs for a public semaphore). Alternatively, all close operations can be performed first, and then the unlink operation, after which the object is deleted. Note that if an object is created with the OM_DELETE_ON_LAST_CLOSE flag, it is be deleted with the last close operation, regardless of whether or not it was unlinked. 4.9.2 Object Ownership and Resource Reclamation All objects are owned by the process to which the creator task belongs, or by the kernel if the creator task is a kernel task. When ownership must be changed, for example on a process creation hook, the objOwnerSet( ) can be used. However, its use is restricted—the new owner must be a process or the kernel. All objects that are owned by a process are automatically destroyed when the process dies. All objects that are children of another object are automatically destroyed when the parent object is destroyed. Processes can share public objects through an object lookup-by-name capability (with the xyzOpen( ) set of routines). Sharing objects between processes can only be done by name. When a process terminates, all the private objects that it owns are deleted, regardless of whether or not they are named. All references to public objects in the process are closed (an xyzClose( ) operation is performed). Therefore, any public object is deleted during resource reclamation, regardless of which process created them, if there are no more outstanding xyzOpen( ) calls against it (that is, no other process or the kernel has a reference to it), and the object was already unlinked or was created with the OM_DELETE_ON_LAST_CLOSE option. The exception to this rule is tasks, which are always reclaimed when its creator process dies. When the creator process of a public object dies, but the object survives because it hasn't been unlinked or because another process has a reference to it, ownership of the object is assigned to the kernel. The objShowAll( ) show routine can be used to display information about ownership relations between objects. 195 4 VxWorks Kernel Programmer's Guide, 6.6 4.10 Shared Data Structures The most obvious way for tasks executing in the same memory space (either a process or the kernel) to communicate is by accessing shared data structures. Because all the tasks in a single process or in the kernel exist in a single linear address space, sharing data structures between tasks is trivial; see Figure 4-7. Global variables, linear buffers, ring buffers, linked lists, and pointers can be referenced directly by code running in different contexts. For information about using shared data regions to communicate between processes, see VxWorks Application Programmer’s Guide: Applications and Processes. Figure 4-7 Shared Data Structures TASKS task 1 MEMORY access sharedData sharedData access task 2 sharedData task 3 sharedData access 4.11 Mutual Exclusion While a shared address space simplifies exchange of data, interlocking access to memory is crucial to avoid contention. Many methods exist for obtaining exclusive access to resources, and vary only in the scope of the exclusion. Such methods include disabling interrupts, disabling preemption, and resource locking with semaphores. For information about POSIX mutexes, see 5.11 POSIX Thread Mutexes and Condition Variables, p.273. 196 4 Multitasking 4.11 Mutual Exclusion 4.11.1 Interrupt Locks and Latency The most powerful method available for mutual exclusion is the disabling of interrupts with the intLock( ) routine. Such a lock guarantees exclusive access to the CPU: funcA () { int lock = intLock(); . . /* critical region of code that cannot be interrupted */ . intUnlock (lock); } While this solves problems involving mutual exclusion with ISRs, it is inappropriate as a general-purpose mutual-exclusion method for most real-time systems, because it prevents the system from responding to external events for the duration of these locks. Interrupt latency is unacceptable whenever an immediate response to an external event is required. However, interrupt locking can sometimes be necessary where mutual exclusion involves ISRs. In any situation, keep the duration of interrupt lockouts short. For information about ISRs, see 4.20 Interrupt Service Routines, p.241. ! WARNING: Invoking a VxWorks system routine with interrupts locked may result in interrupts being re-enabled for an unspecified period of time. If the called routine blocks, or results in a higher priority task becoming eligible for execution (READY), interrupts will be re-enabled while another task executes, or while the kernel is idle. NOTE: The intLock( ) routine is provided for the UP configuration of VxWorks, but not the SMP configuration. Several alternative are available for SMP systems, including the ISR-callable spinlock, which defaults to intLock( ) behavior in a UP system. For more information, see 15.6.1 ISR-Callable Spinlocks, p.682 and 15.15 Migrating Code to VxWorks SMP, p.702. 4.11.2 Preemptive Locks and Latency Disabling preemption with the taskLock( ) routine offers a somewhat less restrictive form of mutual exclusion. While no other task is allowed to preempt the current executing task, ISRs are able to execute: 197 4 VxWorks Kernel Programmer's Guide, 6.6 funcA () { taskLock (); . . /* critical region of code that cannot be interrupted */ . taskUnlock (); } However, this method can lead to unacceptable real-time response. Tasks of higher priority are unable to execute until the locking task leaves the critical region, even though the higher-priority task is not itself involved with the critical region. While this kind of mutual exclusion is simple, if you use it, be sure to keep the duration short. Semaphores provide a better mechanism; see 4.12 Semaphores, p.198. ! WARNING: The critical region code should not block. If it does, preemption could be re-enabled. NOTE: The taskLock( ) and taskUnlock( ) routines are provided for the UP configuration of VxWorks, but not the SMP configuration. Several alternative are available for SMP systems, including task-only spinlocks, which default to taskLock( ) and taskUnlock( ) behavior in a UP system. For more information, see 15.6.2 Task-Only Spinlocks, p.682 and 15.15 Migrating Code to VxWorks SMP, p.702. 4.12 Semaphores VxWorks semaphores are highly optimized and provide the fastest intertask communication mechanism in VxWorks. Semaphores are the primary means for addressing the requirements of both mutual exclusion and task synchronization, as described below: ■ For mutual exclusion, semaphores interlock access to shared resources. They provide mutual exclusion with finer granularity than either interrupt disabling or preemptive locks, discussed in 4.11 Mutual Exclusion, p.196. ■ For synchronization, semaphores coordinate a task’s execution with external events. 198 4 Multitasking 4.12 Semaphores NOTE: Semaphores provide full memory barriers, which is of particular significance for the SMP configuration of VxWorks. For more information, see 15.8 Memory Barriers, p.687. VxWorks provides the following types of semaphores, which are optimized for different types of uses: binary The fastest, most general-purpose semaphore. Optimized for synchronization or mutual exclusion. For more information, see 4.12.2 Binary Semaphores, p.201. mutual exclusion A special binary semaphore optimized for problems inherent in mutual exclusion: priority inversion, deletion safety, and recursion. For more information, see 4.12.3 Mutual-Exclusion Semaphores, p.205. counting Like the binary semaphore, but keeps track of the number of times a semaphore is given. Optimized for guarding multiple instances of a resource. For more information, see 4.12.4 Counting Semaphores, p.208. read/write A special type of semaphore that provides mutual exclusion for tasks that need write access to an object, and concurrent access for tasks that only need read access to the object. This type of semaphore is particularly useful for SMP systems. For more information, see 4.12.5 Read/Write Semaphores, p.209. VxWorks semaphores can be created as private objects, which are accessible only within the memory space in which they were created (kernel or process); or as public objects, which accessible throughout the system. For more information, see 4.9 Public and Private Objects, p.194. VxWorks not only provides the semaphores designed expressly for VxWorks, but also POSIX semaphores, designed for portability. An alternate semaphore library provides the POSIX-compliant semaphore interface; see 5.13 POSIX Semaphores, p.289. NOTE: The semaphores described here are for use with UP and SMP configurations of VxWorks. The optional product VxMP provides semaphores that can be used in an asymmetric multiprocessor (AMP) system, in the VxWorks kernel (but not in UP or SMP systems). For more information, see 16. Shared-Memory Objects: VxMP. 199 4 VxWorks Kernel Programmer's Guide, 6.6 4.12.1 Semaphore Control In most cases, VxWorks provides a single, uniform interface for semaphore control—instead of defining a full set of semaphore control routines specific to each type of semaphore. The exceptions are the creation routines, which are specific to each semaphore type; and the give and take routines for read/write semaphores, which support read and write modes for each operation. Table 4-12 lists the semaphore control routines. Table 4-12 Semaphore Control Routines Call Description semBCreate( ) Allocates and initializes a binary semaphore. semMCreate( ) Allocates and initializes a mutual-exclusion semaphore. semCCreate( ) Allocates and initializes a counting semaphore. semRWCreate( ) Allocates and initializes a read/write semaphore. semDelete( ) Terminates and frees a semaphore. semTake( ) Takes a binary, mutual-exclusion, or counting semaphore., or a read/write semaphore in write mode. semRTake( ) Takes a read/write semaphore in read mode. semWTake( ) Takes a read/write semaphore in write mode. semGive( ) Gives a binary, mutual -exclusion, or counting semaphore. semRWGive( ) Gives a read/write semaphore. semFlush( ) Unblocks all tasks that are waiting for a semaphore. semExchange( ) Provides for an atomic give and exchange of semaphores in SMP systems. The creation routines return a semaphore ID that serves as a handle on the semaphore during subsequent use by the other semaphore-control routines. When a semaphore is created, the queue type is specified. Tasks pending on a semaphore can be queued in priority order (SEM_Q_PRIORITY) or in first-in first-out order (SEM_Q_FIFO). 200 4 Multitasking 4.12 Semaphores ! WARNING: The semDelete( ) call terminates a semaphore and deallocates all associated memory. Take care when deleting semaphores, particularly those used for mutual exclusion, to avoid deleting a semaphore that another task still requires. Do not delete a semaphore unless the same task first succeeds in taking it. 4 Static Instantiation of Semaphores The semaphore creation routines listed in Table 4-12 perform a dynamic, two-step operation, in which memory is allocated for the semaphore object at runtime, and then the object is initialized. Semaphores (and other VxWorks objects) can also be statically instantiated—which means that their memory is allocated for the object at compile time—and the object is then initialized at runtime with an initialization routine. For information about static instantiation, see 2.6.4 Static Instantiation of Kernel Objects, p.56. For information about semaphore initialization routines, see the VxWorks API references. 4.12.2 Binary Semaphores The general-purpose binary semaphore is capable of addressing the requirements of both forms of task coordination: mutual exclusion and synchronization. The binary semaphore has the least overhead associated with it, making it particularly applicable to high-performance requirements. The mutual-exclusion semaphore described in 4.12.3 Mutual-Exclusion Semaphores, p.205 is also a binary semaphore, but it has been optimized to address problems inherent to mutual exclusion. Alternatively, the binary semaphore can be used for mutual exclusion if the advanced features of the mutual-exclusion semaphore are deemed unnecessary. A binary semaphore can be viewed as a flag that is available (full) or unavailable (empty). When a task takes a binary semaphore, with semTake( ), the outcome depends on whether the semaphore is available (full) or unavailable (empty) at the time of the call; see Figure 4-8. If the semaphore is available (full), the semaphore becomes unavailable (empty) and the task continues executing immediately. If the semaphore is unavailable (empty), the task is put on a queue of blocked tasks and enters a state of pending on the availability of the semaphore. 201 VxWorks Kernel Programmer's Guide, 6.6 Figure 4-8 Taking a Semaphore no no semaphore available? NO_WAIT timeout = yes yes task continues; semaphore taken task is pended for timeout value task continues; semaphore not taken When a task gives a binary semaphore, using semGive( ), the outcome also depends on whether the semaphore is available (full) or unavailable (empty) at the time of the call; see Figure 4-9. If the semaphore is already available (full), giving the semaphore has no effect at all. If the semaphore is unavailable (empty) and no task is waiting to take it, then the semaphore becomes available (full). If the semaphore is unavailable (empty) and one or more tasks are pending on its availability, then the first task in the queue of blocked tasks is unblocked, and the semaphore is left unavailable (empty). Figure 4-9 Giving a Semaphore no semaphore available? yes task continues; semaphore remains unchanged 202 no tasks pended? yes task at front of queue made ready; semaphore remains unavailable task continues, semaphore made available 4 Multitasking 4.12 Semaphores Mutual Exclusion Binary semaphores interlock access to a shared resource efficiently. Unlike disabling interrupts or preemptive locks, binary semaphores limit the scope of the mutual exclusion to only the associated resource. In this technique, a semaphore is created to guard the resource. Initially the semaphore is available (full). /* includes */ #include #include SEM_ID semMutex; /* Create a binary semaphore that is initially full. Tasks * * blocked on semaphore wait in priority order. */ semMutex = semBCreate (SEM_Q_PRIORITY, SEM_FULL); When a task wants to access the resource, it must first take that semaphore. As long as the task keeps the semaphore, all other tasks seeking access to the resource are blocked from execution. When the task is finished with the resource, it gives back the semaphore, allowing another task to use the resource. Thus, all accesses to a resource requiring mutual exclusion are bracketed with semTake( ) and semGive( ) pairs: semTake (semMutex, WAIT_FOREVER); . . /* critical region, only accessible by a single task at a time */ . semGive (semMutex); Synchronization When used for task synchronization, a semaphore can represent a condition or event that a task is waiting for. Initially, the semaphore is unavailable (empty). A task or ISR signals the occurrence of the event by giving the semaphore. Another task waits for the semaphore by calling semTake( ). The waiting task blocks until the event occurs and the semaphore is given. (See 4.20 Interrupt Service Routines, p.241 for a complete discussion of ISRs) Note the difference in sequence between semaphores used for mutual exclusion and those used for synchronization. For mutual exclusion, the semaphore is initially full, and each task first takes, then gives back the semaphore. For synchronization, the semaphore is initially empty, and one task waits to take the semaphore given by another task. 203 4 VxWorks Kernel Programmer's Guide, 6.6 In Example 4-2, the init( ) routine creates the binary semaphore, attaches an ISR to an event, and spawns a task to process the event. The routine task1( ) runs until it calls semTake( ). It remains blocked at that point until an event causes the ISR to call semGive( ). When the ISR completes, task1( ) executes to process the event. There is an advantage of handling event processing within the context of a dedicated task: less processing takes place at interrupt level, thereby reducing interrupt latency. This model of event processing is recommended for real-time applications. Example 4-2 Using Semaphores for Task Synchronization /* This example shows the use of semaphores for task synchronization. */ /* includes */ #include #include #include /* replace arch with architecture type */ SEM_ID syncSem; /* ID of sync semaphore */ init ( int someIntNum ) { /* connect interrupt service routine */ intConnect (INUM_TO_IVEC (someIntNum), eventInterruptSvcRout, 0); /* create semaphore */ syncSem = semBCreate (SEM_Q_FIFO, SEM_EMPTY); /* spawn task used for synchronization. */ taskSpawn ("sample", 100, 0, 20000, task1, 0,0,0,0,0,0,0,0,0,0); } task1 (void) { ... semTake (syncSem, WAIT_FOREVER); /* wait for event to occur */ printf ("task 1 got the semaphore\n"); ... /* process event */ } eventInterruptSvcRout (void) { ... semGive (syncSem); /* let task 1 process event */ ... } Broadcast synchronization allows all processes that are blocked on the same semaphore to be unblocked atomically. Correct application behavior often requires a set of tasks to process an event before any task of the set has the 204 4 Multitasking 4.12 Semaphores opportunity to process further events. The routine semFlush( ) addresses this class of synchronization problem by unblocking all tasks pended on a semaphore. 4.12.3 Mutual-Exclusion Semaphores 4 The mutual-exclusion semaphore is a specialized binary semaphore designed to address issues inherent in mutual exclusion, including priority inversion, deletion safety, and recursive access to resources. The fundamental behavior of the mutual-exclusion semaphore is identical to the binary semaphore, with the following exceptions: ■ ■ ■ ■ It can be used only for mutual exclusion. It can be given only by the task that took it. It cannot be given from an ISR. The semFlush( ) operation is illegal. Priority Inversion Figure 4-10 illustrates a situation called priority inversion. Priority Inversion t1 t1 HIGH priority Figure 4-10 LOW t2 t3 t3 t3 time KEY: = take semaphore = preemption = give semaphore = priority inheritance/release = own semaphore = block 205 VxWorks Kernel Programmer's Guide, 6.6 Priority inversion arises when a higher-priority task is forced to wait an indefinite period of time for a lower-priority task to complete. Consider the scenario in Figure 4-10: t1, t2, and t3 are tasks of high, medium, and low priority, respectively. t3 has acquired some resource by taking its associated binary guard semaphore. When t1 preempts t3 and contends for the resource by taking the same semaphore, it becomes blocked. If we could be assured that t1 would be blocked no longer than the time it normally takes t3 to finish with the resource, there would be no problem because the resource cannot be preempted. However, the low-priority task is vulnerable to preemption by medium-priority tasks (like t2), which could inhibit t3 from relinquishing the resource. This condition could persist, blocking t1 for an indefinite period of time. The mutual-exclusion semaphore has the option SEM_INVERSION_SAFE, which enables a priority-inheritance policy. The priority-inheritance policy assures that a task that holds a resource executes at the priority of the highest-priority task blocked on that resource. Once the task priority has been elevated, it remains at the higher level until all mutual-exclusion semaphores that have contributed to the tasks elevated priority are released. Hence, the inheriting task is protected from preemption by any intermediate-priority tasks. This option must be used in conjunction with a priority queue (SEM_Q_PRIORITY). Priority Inheritance t1 HIGH t3 t1 priority Figure 4-11 LOW t2 t3 time KEY: 206 = take semaphore = preemption = give semaphore = priority inheritance/release = own semaphore = block 4 Multitasking 4.12 Semaphores In Figure 4-11, priority inheritance solves the problem of priority inversion by elevating the priority of t3 to the priority of t1 during the time t1 is blocked on the semaphore. This protects t3, and indirectly t1, from preemption by t2. The following example creates a mutual-exclusion semaphore that uses the priority inheritance policy: semId = semMCreate (SEM_Q_PRIORITY | SEM_INVERSION_SAFE); Deletion Safety Another problem of mutual exclusion involves task deletion. Within a critical region guarded by semaphores, it is often desirable to protect the executing task from unexpected deletion. Deleting a task executing in a critical region can be catastrophic. The resource might be left in a corrupted state and the semaphore guarding the resource left unavailable, effectively preventing all access to the resource. The primitives taskSafe( ) and taskUnsafe( ) provide one solution to task deletion. However, the mutual-exclusion semaphore offers the option SEM_DELETE_SAFE, which enables an implicit taskSafe( ) with each semTake( ), and a taskUnsafe( ) with each semGive( ). In this way, a task can be protected from deletion while it has the semaphore. This option is more efficient than the primitives taskSafe( ) and taskUnsafe( ), as the resulting code requires fewer entrances to the kernel. semId = semMCreate (SEM_Q_FIFO | SEM_DELETE_SAFE); Recursive Resource Access Mutual-exclusion semaphores can be taken recursively. This means that the semaphore can be taken more than once by the task that holds it before finally being released. Recursion is useful for a set of routines that must call each other but that also require mutually exclusive access to a resource. This is possible because the system keeps track of which task currently holds the mutual-exclusion semaphore. Before being released, a mutual-exclusion semaphore taken recursively must be given the same number of times it is taken. This is tracked by a count that increments with each semTake( ) and decrements with each semGive( ). 207 4 VxWorks Kernel Programmer's Guide, 6.6 Example 4-3 Recursive Use of a Mutual-Exclusion Semaphore /* Function A requires access to a resource which it acquires by taking * mySem; * Function A may also need to call function B, which also requires mySem: */ /* includes */ #include #include SEM_ID mySem; /* Create a mutual-exclusion semaphore. */ init () { mySem = semMCreate (SEM_Q_PRIORITY); } funcA () { semTake (mySem, WAIT_FOREVER); printf ("funcA: Got mutual-exclusion semaphore\n"); ... funcB (); ... semGive (mySem); printf ("funcA: Released mutual-exclusion semaphore\n"); } funcB () { semTake (mySem, WAIT_FOREVER); printf ("funcB: Got mutual-exclusion semaphore\n"); ... semGive (mySem); printf ("funcB: Releases mutual-exclusion semaphore\n"); } 4.12.4 Counting Semaphores Counting semaphores are another means to implement task synchronization and mutual exclusion. The counting semaphore works like the binary semaphore except that it keeps track of the number of times a semaphore is given. Every time a semaphore is given, the count is incremented; every time a semaphore is taken, the count is decremented. When the count reaches zero, a task that tries to take the semaphore is blocked. As with the binary semaphore, if a semaphore is given and a task is blocked, it becomes unblocked. However, unlike the binary semaphore, if a semaphore is given and no tasks are blocked, then the count is incremented. This means that a semaphore that is given twice can be taken twice without blocking. 208 4 Multitasking 4.12 Semaphores Table 4-13 shows an example time sequence of tasks taking and giving a counting semaphore that was initialized to a count of 3. Table 4-13 Counting Semaphore Example Semaphore Call Count after Call semCCreate( ) 3 Semaphore initialized with an initial count of 3. semTake( ) 2 Semaphore taken. semTake( ) 1 Semaphore taken. semTake( ) 0 Semaphore taken. semTake( ) 0 Task blocks waiting for semaphore to be available. semGive( ) 0 Task waiting is given semaphore. semGive( ) 1 No task waiting for semaphore; count incremented. 4 Resulting Behavior Counting semaphores are useful for guarding multiple copies of resources. For example, the use of five tape drives might be coordinated using a counting semaphore with an initial count of 5, or a ring buffer with 256 entries might be implemented using a counting semaphore with an initial count of 256. The initial count is specified as an argument to the semCCreate( ) routine. 4.12.5 Read/Write Semaphores Read/write semaphores provide enhanced performance for applications that can effectively make use of differentiation between read access to a resource, and write access to a resource. A read/write semaphore can be taken in either read mode or write mode. They are particularly suited to SMP systems (for information about the SMP configuration of VxWorks, see 15. VxWorks SMP). A task holding a read/write semaphore in write mode has exclusive access to a resource. On the other hand, a task holding a read/write semaphore in read mode does not have exclusive access. More than one task can take a read/write semaphore in read mode, and gain access to the same resource. Because it is exclusive, write-mode permits only serial access to a resource, while while read-mode allows shared or concurrent access. In a multiprocessor system, more than one task (running in different CPUs) can have read-mode access to a 209 VxWorks Kernel Programmer's Guide, 6.6 resource in a truly concurrent manner. In a uniprocessor system, however, access is shared but the concurrency is virtual. More than one task can have read-mode access to a resource at the same time, but since the tasks do not run simultaneously, access is effectively multiplexed. All tasks that hold a read/write semaphore in read mode must give it up before any task can take it in write mode. Specification of Read or Write Mode A read/write semaphore differs from other types of semaphore in that the access mode must be specified when the semaphore is taken. The mode determines whether the access is exclusive (write mode), or if concurrent access is allowed (read mode). Different APIs correspond to the different modes of access, as follows: ■ ■ semRTake( ) for read (exclusive) mode semWTake( ) for write (concurrent) mode You can also use semTake( ) on a read/write semaphore, but the behavior is the same as semWTake( ). And you can use semGive( ) on a read/write semaphore as long as the task owns it is in the same mode. For more information about read/write semaphore APIs, see Table 4-12 and the VxWorks API references. When a task takes a read/write semaphore in write mode, the behavior is identical to that of a mutex semaphore. The task owns the semaphore exclusively. An attempt to give a semaphore held by one task in this mode by task results in a return value of ERROR. When a task takes a read/write semaphore in read mode, the behavior is different from other semaphores. It does not provide exclusive access to a resource (does not protect critical sections), and the semaphore may be concurrently held in read mode by more than one task. The maximum number of tasks that can take a read/write semaphore in read mode can be specified when the semaphore is created with the create routine call. The system maximum for all read/write semaphores can also be set with SEM_RW_MAX_CONCURRENT_READERS component parameter. By default it is set to 32. If the number of tasks is not specified when the create routine is called, the system default is used. 210 4 Multitasking 4.12 Semaphores Read/write semaphores can be taken recursively in both read and write mode. Optionally, priority inheritance and deletion safety are available for each mode. Precedence for Write Access Operations 4 When a read/write semaphore becomes available, precedence is given to pended tasks that require write access, regardless of their task priority relative to pended tasks that require read access. That is, the highest priority task attempting a semWTake( ) operation gets the semaphore, even if there are higher priority tasks attempting a semRTake( ). Precedence for write access helps to ensure that the protected resource is kept current because there is no delay due to read operations occurring before a pending write operation can take place. Note, however, that all read-mode takes must be given before a read/write semaphore can be taken in write mode. Read/Write Semaphores and System Performance The performance of systems that implement read/write semaphores for their intended use should be enhanced, particularly so in SMP systems. However, due to the additional bookkeeping overhead involved in tracking multiple read-mode owners, performance is likely to be adversely affected in those cases where the feature does fit a clear design goal. In particular, interrupt latency in a uniprocessor system and kernel latency in a multiprocessor system may be adversely affected. 4.12.6 Special Semaphore Options The uniform VxWorks semaphore interface includes three special options: timeouts, queues, and use with VxWorks events. These options are not available for either the read/write semaphores described in 4.12.5 Read/Write Semaphores, p.209, or the POSIX-compliant semaphores described in 5.13 POSIX Semaphores, p.289. 211 VxWorks Kernel Programmer's Guide, 6.6 Timeouts As an alternative to blocking until a semaphore becomes available, semaphore take operations can be restricted to a specified period of time. If the semaphore is not taken within that period, the take operation fails. This behavior is controlled by a parameter to semTake( ) and the take routines for read/write semaphores that specifies the amount of time in ticks that the task is willing to wait in the pended state. If the task succeeds in taking the semaphore within the allotted time, the take routine returns OK. The errno set when a take routine returns ERROR due to timing out before successfully taking the semaphore depends upon the timeout value passed. A semTake( ) with NO_WAIT (0), which means do not wait at all, sets errno to S_objLib_OBJ_UNAVAILABLE. A semTake( ) with a positive timeout value returns S_objLib_OBJ_TIMEOUT. A timeout value of WAIT_FOREVER (-1) means wait indefinitely. Queues VxWorks semaphores include the ability to select the queuing mechanism employed for tasks blocked on a semaphore. They can be queued based on either of two criteria: first-in first-out (FIFO) order, or priority order; see Figure 4-12. 212 4 Multitasking 4.13 Message Queues Figure 4-12 Task Queue Types FIFO QUEUE PRIORITY QUEUE 4 TCB TCB TCB TCB 200 120 TCB TCB 90 100 80 TCB 110 140 TCB priority 110 Priority ordering better preserves the intended priority structure of the system at the expense of some overhead in take operations because of sorting the tasks by priority. A FIFO queue requires no priority sorting overhead and leads to constant-time performance. The selection of queue type is specified during semaphore creation with the semaphore creation routine. Semaphores using the priority inheritance option (SEM_INVERSION_SAFE) must select priority-order queuing. 4.12.7 Semaphores and VxWorks Events Semaphores can send VxWorks events to a specified task when they becomes free. For more information, see 4.15 VxWorks Events, p.219. 4.13 Message Queues Modern real-time applications are constructed as a set of independent but cooperating tasks. While semaphores provide a high-speed mechanism for the synchronization and interlocking of tasks, often a higher-level mechanism is 213 VxWorks Kernel Programmer's Guide, 6.6 necessary to allow cooperating tasks to communicate with each other. In VxWorks, the primary intertask communication mechanism within a single CPU is message queues. For information about socket-based message communication across memory spaces (kernel and processes), and between multiple nodes, see 4.16 Message Channels, p.226. Message queues allow a variable number of messages, each of variable length, to be queued. Tasks and ISRs can send messages to a message queue, and tasks can receive messages from a message queue. Figure 4-13 Full Duplex Communication Using Message Queues message queue 1 message task 1 task 2 message message queue 2 Multiple tasks can send to and receive from the same message queue. Full-duplex communication between two tasks generally requires two message queues, one for each direction; see Figure 4-13. VxWorks message queues can be created as private objects, which accessible only within the memory space in which they were created (process or kernel); or as public objects, which accessible throughout the system. For more information, see 4.9 Public and Private Objects, p.194. There are two message-queue subroutine libraries in VxWorks. The first of these, msgQLib, provides VxWorks message queues, designed expressly for VxWorks; the second, mqPxLib, is compliant with the POSIX standard (1003.1b) for real-time extensions. See 5.13.1 Comparison of POSIX and VxWorks Semaphores, p.290 for a discussion of the differences between the two message-queue designs. 214 4 Multitasking 4.13 Message Queues 4.13.1 VxWorks Message Queue Routines VxWorks message queues are created, used, and deleted with the routines shown in Table 4-14. This library provides messages that are queued in FIFO order, with a single exception: there are two priority levels, and messages marked as high priority are attached to the head of the queue. Table 4-14 VxWorks Message Queue Control Call Description msgQCreate( ) Allocates and initializes a message queue. msgQDelete( ) Terminates and frees a message queue. msgQSend( ) Sends a message to a message queue. msgQReceive( ) Receives a message from a message queue. A message queue is created with msgQCreate( ). Its parameters specify the maximum number of messages that can be queued in the message queue and the maximum length in bytes of each message. Enough buffer space is allocated for the specified number and length of messages. A task or ISR sends a message to a message queue with msgQSend( ). If no tasks are waiting for messages on that queue, the message is added to the queue’s buffer of messages. If any tasks are already waiting for a message from that message queue, the message is immediately delivered to the first waiting task. A task receives a message from a message queue with msgQReceive( ). If messages are already available in the message queue’s buffer, the first message is immediately dequeued and returned to the caller. If no messages are available, then the calling task blocks and is added to a queue of tasks waiting for messages. This queue of waiting tasks can be ordered either by task priority or FIFO, as specified in an option parameter when the queue is created. Timeouts Both msgQSend( ) and msgQReceive( ) take timeout parameters. When sending a message, the timeout specifies how many ticks to wait for buffer space to become available, if no space is available to queue the message. When receiving a message, the timeout specifies how many ticks to wait for a message to become available, if no message is immediately available. As with semaphores, the value of the timeout parameter can have the special values of NO_WAIT (0), meaning always return immediately, or WAIT_FOREVER (-1), meaning never time out the routine. 215 4 VxWorks Kernel Programmer's Guide, 6.6 Urgent Messages The msgQSend( ) function allows specification of the priority of the message as either normal (MSG_PRI_NORMAL) or urgent (MSG_PRI_URGENT). Normal priority messages are added to the tail of the list of queued messages, while urgent priority messages are added to the head of the list. Example 4-4 VxWorks Message Queues /* In this example, task t1 creates the message queue and sends a message * to task t2. Task t2 receives the message from the queue and simply * displays the message. */ /* includes */ #include #include /* defines */ #define MAX_MSGS (10) #define MAX_MSG_LEN (100) MSG_Q_ID myMsgQId; task2 (void) { char msgBuf[MAX_MSG_LEN]; /* get message from queue; if necessary wait until msg is available */ if (msgQReceive(myMsgQId, msgBuf, MAX_MSG_LEN, WAIT_FOREVER) == ERROR) return (ERROR); /* display message */ printf ("Message from task 1:\n%s\n", msgBuf); } #define MESSAGE "Greetings from Task 1" task1 (void) { /* create message queue */ if ((myMsgQId = msgQCreate (MAX_MSGS, MAX_MSG_LEN, MSG_Q_PRIORITY)) == NULL) return (ERROR); /* send a normal priority message, blocking if queue is full */ if (msgQSend (myMsgQId, MESSAGE, sizeof (MESSAGE), WAIT_FOREVER, MSG_PRI_NORMAL) == ERROR) return (ERROR); } 216 4 Multitasking 4.13 Message Queues Queuing VxWorks message queues include the ability to select the queuing mechanism employed for tasks blocked on a message queue. The MSG_Q_FIFO and MSG_Q_PRIORITY options are provided to specify (to the msgQCreate( ) and msgQOpen( ) routines) the queuing mechanism that should be used for tasks that pend on msgQSend( ) and msgQReceive( ). 4.13.2 Displaying Message Queue Attributes The VxWorks show( ) command produces a display of the key message queue attributes, for either kind of message queue. For example, if myMsgQId is a VxWorks message queue, the output is sent to the standard output device, and looks like the following from the shell (using the C interpreter): -> show myMsgQId Message Queue Id Task Queuing Message Byte Len Messages Max Messages Queued Receivers Blocked Send timeouts Receive timeouts : : : : : : : 0x3adaf0 FIFO 4 30 14 0 0 : 0 4.13.3 Servers and Clients with Message Queues Real-time systems are often structured using a client-server model of tasks. In this model, server tasks accept requests from client tasks to perform some service, and usually return a reply. The requests and replies are usually made in the form of intertask messages. In VxWorks, message queues or pipes (see 4.14 Pipes, p.218) are a natural way to implement this functionality. For example, client-server communications might be implemented as shown in Figure 4-14. Each server task creates a message queue to receive request messages from clients. Each client task creates a message queue to receive reply messages from servers. Each request message includes a field containing the msgQId of the client’s reply message queue. A server task’s main loop consists of reading request messages from its request message queue, performing the request, and sending a reply to the client’s reply message queue. 217 4 VxWorks Kernel Programmer's Guide, 6.6 Figure 4-14 Client-Server Communications Using Message Queues reply queue 1 message client 1 request queue server task message client 2 reply queue 2 message The same architecture can be achieved with pipes instead of message queues, or by other means that are tailored to the needs of the particular application. 4.13.4 Message Queues and VxWorks Events Message queues can send VxWorks events to a specified task when a message arrives on the queue and no task is waiting on it. For more information, see 4.15 VxWorks Events, p.219. 4.14 Pipes Pipes provide an alternative interface to the message queue facility that goes through the VxWorks I/O system. Pipes are virtual I/O devices managed by the 218 4 Multitasking 4.15 VxWorks Events driver pipeDrv. The routine pipeDevCreate( ) creates a pipe device and the underlying message queue associated with that pipe. The call specifies the name of the created pipe, the maximum number of messages that can be queued to it, and the maximum length of each message: status = pipeDevCreate ("/pipe/name", max_msgs, max_length); 4 The created pipe is a normally named I/O device. Tasks can use the standard I/O routines to open, read, and write pipes, and invoke ioctl routines. As they do with other I/O devices, tasks block when they read from an empty pipe until data is available, and block when they write to a full pipe until there is space available. Like message queues, ISRs can write to a pipe, but cannot read from a pipe. As I/O devices, pipes provide one important feature that message queues cannot—the ability to be used with select( ). This routine allows a task to wait for data to be available on any of a set of I/O devices. The select( ) routine also works with other asynchronous I/O devices including network sockets and serial devices. Thus, by using select( ), a task can wait for data on a combination of several pipes, sockets, and serial devices; see 7.4.9 Pending on Multiple File Descriptors with select( ), p.374. Pipes allow you to implement a client-server model of intertask communications; see 4.13.3 Servers and Clients with Message Queues, p.217. 4.15 VxWorks Events VxWorks events provide a means of communication and synchronization between tasks and other tasks, interrupt service routines (ISRs) and tasks, semaphores and tasks, and message queues and tasks.1 Events can be used as a lighter-weight alternative to binary semaphores for task-to-task and ISR-to-task synchronization (because no object must be created). They can also be used to notify a task that a semaphore has become available, or that a message has arrived on a message queue. The events facility provides a mechanism for coordinating the activity of a task using up to thirty-two events that can be sent to it by other tasks, ISRs, semaphores, 1. VxWorks events are based on pSOS operating system events. VxWorks introduced functionality similar to pSOS events (but with enhancements) with the VxWorks 5.5 release. 219 VxWorks Kernel Programmer's Guide, 6.6 and message queues. A task can wait on multiple events from multiple sources. Events thereby provide a means for coordination of complex matrix of activity without allocation of additional system resources. Each task has 32 event flags, bit-wise encoded in a 32-bit word (bits 25 to 32 are reserved for Wind River use). These flags are stored in the task’s event register. Note that an event flag itself has no intrinsic meaning. The significance of each of the 32 event flags depends entirely on how any given task is coded to respond to their being set. There is no mechanism for recording how many times any given event has been received by a task. Once a flag has been set, its being set again by the same or a different sender is essentially an invisible operation. Events are similar to signals in that they are sent to a task asynchronously; but differ in that receipt is synchronous. That is, the receiving task must call a routine to receive at will, and can choose to pend while waiting for events to arrive. Unlike signals, therefore, events do not require a handler. For a code example of how events can be used, see the eventLib API reference. NOTE: VxWorks events, which are also simply referred to as events in this section, should not be confused with System Viewer events. Configuring VxWorks for Events To provide events facilities, VxWorks must be configured with the INCLUDE_VXEVENTS component. 4.15.1 Preparing a Task to Receive Events A task can pend on one or more events, or simply check on which events have been received, with a call to eventReceive( ). The routine specifies which events to wait for, and provides options for waiting for one or all of those events. It also provides various options for how to manage unsolicited events. In order for a task to receive events from a semaphore or a message queue, however, it must first register with the specific object, using semEvStart( ) for a semaphore or msgQEvStart( ) for a message queue. Only one task can be registered with any given semaphore or message queue at a time. The semEvStart( ) routine identifies the semaphore and the events that it should send to the task when the semaphore is free. It also provides a set of options to specify whether the events are sent only the first time the semaphore is free, or each time; whether to send events if the semaphore is free at the time of 220 4 Multitasking 4.15 VxWorks Events registration; and whether a subsequent semEvStart( ) call from another task is allowed to take effect (and to unregister the previously registered task). Once a task has registered with a semaphore, every time the semaphore is released with semGive( ), and as long as no other tasks are pending on it, the semaphore sends events to the registered task. To request that the semaphore stop sending events to it, the registered task calls semEvStop( ). Registration with a message queue is similar to registration with a semaphore. The msgQEvStart( ) routine identifies the message queue and the events that it should send to the task when a message arrives and no tasks are pending on it. It provides a set of options to specify whether the events are sent only the first time a message is available, or each time; whether a subsequent call to msgQEvStart( ) from another task is allowed to take effect (and to unregister the previously registered task). Once a task has registered with a message queue, every time the message queue receives a message and there are no tasks pending on it, the message queue sends events to the registered task. To request that the message queue stop sending events to it, the registered task calls msgQEvStop( ). 4.15.2 Sending Events to a Task Tasks and ISRs can send specific events to a task using eventSend( ), whether or not the receiving task is prepared to make use of them. Semaphores and message queues send events automatically to tasks that have registered for notification with semEvStart( ) or msgQEvStart( ), respectively. These objects send events when they are free. The conditions under which objects are free are as follows: Mutex Semaphore A mutex semaphore is considered free when it no longer has an owner and no task is pending on it. For example, following a call to semGive( ), the semaphore will not send events if another task is pending on a semTake( ) for the same semaphore. Binary Semaphore A binary semaphore is considered free when no task owns it and no task is waiting for it. 221 4 VxWorks Kernel Programmer's Guide, 6.6 Counting Semaphore A counting semaphore is considered free when its count is nonzero and no task is pending on it. Events cannot, therefore, be used as a mechanism to compute the number of times a semaphore is released or given. Message Queue A message queue is considered free when a message is present in the queue and no task is pending for the arrival of a message in that queue. Events cannot, therefore, be used as a mechanism to compute the number of messages sent to a message queue. Note that just because an object has been released does not mean that it is free. For example, if a semaphore is given, it is released; but it is not free if another task is waiting for it at the time it is released. When two or more tasks are constantly exchanging ownership of an object, it is therefore possible that the object never becomes free, and never sends events. Also note that when a semaphore or message queue sends events to a task to indicate that it is free, it does not mean that the object is in any way reserved for the task. A task waiting for events from an object unpends when the resource becomes free, but the object may be taken in the interval between notification and unpending. The object could be taken by a higher priority task if the task receiving the event was pended in eventReceive( ). Or a lower priority task might steal the object: if the task receiving the event was pended in some routine other than eventReceive( ), a low priority task could execute and (for example) perform a semTake( ) after the event is sent, but before the receiving task unpends from the blocking call. There is, therefore, no guarantee that the resource will still be available when the task subsequently attempts to take ownership of it. ! WARNING: Because events cannot be reserved for an application in any way, care should be taken to ensure that events are used uniquely and unambiguously. Note that events 25 to 32 (VXEV25 to VXEV32) are reserved for Wind River’s use, and should not be used by customers. Third parties should be sure to document their use of events so that their customers do not use the same ones for their applications. Events and Object Deletion If a semaphore or message queue is deleted while a task is waiting for events from it, the task is automatically unpended by the semDelete( ) or msgQDelete( ) implementation. This prevents the task from pending indefinitely while waiting for events from an object that has been deleted. The pending task then returns to 222 4 Multitasking 4.15 VxWorks Events the ready state (just as if it were pending on the semaphore itself) and receives an ERROR return value from the eventReceive( ) call that caused it to pend initially. If, however, the object is deleted between a tasks’ registration call and its eventReceive( ) call, the task pends anyway. For example, if a semaphore is deleted while the task is between the semEvStart( ) and eventReceive( ) calls, the task pends in eventReceive( ), but the event is never sent. It is important, therefore, to use a timeout other than WAIT_FOREVER when object deletion is expected. Events and Task Deletion If a task is deleted before a semaphore or message queue sends events to it, the events can still be sent, but are obviously not received. By default, VxWorks handles this event-delivery failure silently. It can, however, be useful for an application that created an object to be informed when events were not received by the (now absent) task that registered for them. In this case, semaphores and message queues can be created with an option that causes an error to be returned if event delivery fails (the SEM_EVENTSEND_ERROR_NOTIFY and MSG_Q_EVENTSEND_ERROR_NOTIFY options, respectively). The semGive( ) or msgQSend( ) call then returns ERROR when the object becomes free. The error does not mean the semaphore was not given or that the message was not properly delivered. It simply means the resource could not send events to the registered task. Note that a failure to send a message or give a semaphore takes precedence over an events failure. 4.15.3 Accessing Event Flags When events are sent to a task, they are stored in the task’s events register (see 4.15.5 Task Events Register, p.224), which is not directly accessible to the task itself. When the events specified with an eventReceive( ) call have been received and the task unpends, the contents of the events register is copied to a variable that is accessible to the task. When eventReceive( ) is used with the EVENTS_WAIT_ANY option—which means that the task unpends for the first of any of the specified events that it receives—the contents of the events variable can be checked to determine which event caused the task to unpend. The eventReceive( ) routine also provides an option that allows for checking which events have been received prior to the full set being received. 223 4 VxWorks Kernel Programmer's Guide, 6.6 4.15.4 Events Routines The routines used for working with events are listed in Table 4-15. Table 4-15 Events Routines Routine Description eventSend( ) Sends specified events to a task. eventReceive( ) Pends a task until the specified events have been received. Can also be used to check what events have been received in the interim. eventClear( ) Clears the calling task’s event register. semEvStart( ) Registers a task to be notified of semaphore availability. semEvStop( ) Unregisters a task that had previously registered for notification of semaphore availability. msgQEvStart( ) Registers a task to be notified of message arrival on a message queue when no recipients are pending. msgQEvStop( ) Unregisters a task that had previously registered for notification of message arrival on a message queue. For more information about these routines, see the VxWorks API references for eventLib, semEvLib, and msgQEvLib. 4.15.5 Task Events Register Each task has its own task events register. The task events register is a 32-bit field used to store the events that the task receives from other tasks (or itself), ISRs, semaphores, and message queues. Events 25 to 32 (VXEV25 or 0x01000000 to VXEV32 or 0x80000000) are reserved for Wind River use only, and should not be used by customers. As noted above (4.15.3 Accessing Event Flags, p.223), a task cannot access the contents of its events registry directly. Table 4-16 describes the routines that affect the contents of the events register. 224 4 Multitasking 4.15 VxWorks Events Table 4-16 Routines That Modify the Task Events Register Routine Effect on the Task Events Register eventReceive( ) Clears or leaves the contents of the task’s events register intact, depending on the options selected. eventClear( ) Clears the contents of the task’s events register. eventSend( ) Writes events to a tasks’s events register. semGive( ) Writes events to the tasks’s events register, if the task is registered with the semaphore. msgQSend( ) Writes events to a task’s events register, if the task is registered with the message queue. 4.15.6 Show Routines and Events For the purpose of debugging systems that make use of events, the taskShow, semShow, and msgQShow libraries display event information. The taskShow library displays the following information: ■ ■ ■ the contents of the event register the desired events the options specified when eventReceive( ) was called The semShow and msgQShow libraries display the following information: ■ ■ ■ the task registered to receive events the events the resource is meant to send to that task the options passed to semEvStart( ) or msgQEvStart( ) 225 4 VxWorks Kernel Programmer's Guide, 6.6 4.16 Message Channels Message channels are a socket-based facility that provides for inter-task communication within a memory boundary, between memory boundaries (kernel and processes), between nodes (processors) in a multi-node cluster, and between between multiple clusters. In addition to providing a superior alternative to TCP for multi-node intercommunication, message channels provide a useful alternative to message queues for exchanging data between two tasks on a single node. Message channels can be used in both kernel and user (RTP) space. For a comparison of message channels and message queues, see 18.8 Comparison of Message Channels and Message Queues, p.806. For detailed information about message channels, see 18. Message Channels. 4.17 Network Communication To communicate with a peer on a remote networked system, you can use an Internet domain socket or RPC. For information on working with Internet domain sockets or RPC under VxWorks, see the Wind River Network Stack for VxWorks 6 Programmer’s Guide. For information about TIPC networking, see Wind River TIPC for VxWorks 6 Programmer's Guide. 4.18 Signals Signals are an operating system facility designed for handling exceptional conditions and asynchronously altering the flow of control. In many respects signals are the software equivalent to hardware interrupts. Signals generated by the operating system include those produced in response to bus errors and floating point exceptions. The signal facility also provides APIs that can be used to generate and manage signals programmatically. In applications, signals are most appropriate for error and exception handling, and not for a general-purpose inter-task communication. Common uses include using 226 4 Multitasking 4.18 Signals signals to kill processes and tasks, to send signal events when a timer has fired or message has arrived at a message queue, and so on. In accordance with POSIX, VxWorks supports 63 signals, each of which has a unique number and default action (defined in signal.h). The value 0 is reserved for use as the NULL signal. Signals can be raised (sent) from tasks to tasks or to processes. Signals can be either caught (received) or ignored by the receiving task or process. Whether signals are caught or ignored generally depends on the setting of a signal mask. In the kernel, signal masks are specific to tasks, and if no task is set up to receive a specific signal, it is ignored. In user space, signal masks are specific to processes; and some signals, such as SIGKILL and SIGSTOP, cannot be ignored. To manage responses to signals, you can create and register signal handling routines that allow a task to respond to a specific signal in whatever way is useful for your application. A kernel task or interrupt service routine (ISR) can raise a signal for a specific task or process. In the kernel, signal generation and delivery runs in the context of the task or ISR that generates the signal. In accordance with the POSIX standard, a signal sent to a process is handled by the first available task that has been set up to handle the signal in the process. Each kernel task has a signal mask associated with it. The signal mask determines which signals the task accepts. By default, the signal mask is initialized with all signals unblocked (there is no inheritance of mask settings in the kernel). The mask can be changed with sigprocmask( ). Signal handlers in the kernel can be registered for a specific task. A signal handler executes in the receiving task’s context and makes use of that task’s execution stack. The signal handler is invoked even if the task is blocked (suspended or pended). VxWorks provides a software signal facility that includes POSIX routines, UNIX BSD-compatible routines, and native VxWorks routines. The POSIX-compliant signal interfaces include both the basic signaling interface specified in the POSIX standard 1003.1, and the queued-signals extension from POSIX 1003.1b. Additional, non-POSIX APIs provide support for signals between kernel and user applications. These non-POSIX APIs are: taskSigqueue( ), rtpSigqueue( ), rtpTaskSigqueue( ), taskKill( ), rtpKill( ), rtpTaskKill( ), and taskRaise( ). In the VxWorks kernel—for backward compatibility with prior versions of VxWorks—the POSIX API that would take a process identifier as one of their parameters, take a task identifier instead. 227 4 VxWorks Kernel Programmer's Guide, 6.6 NOTE: Wind River recommends that you do not use both POSIX APIs and VxWorks APIs in the same application. Doing so may make a POSIX application non-conformant. NOTE: POSIX signals are handled differently in the kernel and in real-time processes. In the kernel the target of a signal is always a task; but in user space, the target of a signal may be either a specific task or an entire process. NOTE: The VxWorks implementation of sigLib does not impose any special restrictions on operations on SIGKILL, SIGCONT, and SIGSTOP signals such as those imposed by UNIX. For example, the UNIX implementation of signal( ) cannot be called on SIGKILL and SIGSTOP. For information about using signals in processes, see VxWorks Application Programmer’s Guide: Multitasking. In addition to signals, VxWorks also provides another type of event notification with the VxWorks events facility. While signal events are completely asynchronous, VxWorks events are sent asynchronously, but received synchronously, and do not require a signal handler. For more information, see 4.15 VxWorks Events, p.219. 4.18.1 Configuring VxWorks for Signals By default, VxWorks includes the basic signal facility component INCLUDE_SIGNALS. This component automatically initializes signals with sigInit( ). To use the signal event facility, configure VxWorks with the INCLUDE_SIGEVENT component. Note that SIGEV_THREAD option is only supported in processes, and that it requires that VxWorks also be configured with the INCLUDE_SIGEVENTS_THREAD component and full POSIX thread support (the BUNDLE_RTP_POSIX_PSE52 bundle includes everything required for this option). To include POSIX queued signals in the system, configure VxWorks with the INCLUDE_POSIX_SIGNALS component. This component automatically initializes POSIX queued signals with sigqueueInit( ). The sigqueueInit( ) routine allocates buffers for use by sigqueue( ), which requires a buffer for each currently queued signal. A call to sigqueue( ) fails if no buffer is available. 228 4 Multitasking 4.18 Signals The maximum number of queued signals in the kernel is set with the configuration parameter NUM_SIGNAL_QUEUES. The default value is 16. 4.18.2 Basic Signal Routines 4 Signals are in many ways analogous to hardware interrupts. The basic signal facility provides a set of 63 distinct signals. A signal handler binds to a particular signal with sigvec( ) or sigaction( ) in much the same way that an ISR is connected to an interrupt vector with intConnect( ). A signal can be asserted by calling kill( ) or sigqueue( ). This is similar to the occurrence of an interrupt. The sigprocmask( ) routine let signals be selectively inhibited. Certain signals are associated with hardware exceptions. For example, bus errors, illegal instructions, and floating-point exceptions raise specific signals. For a list and description of basic POSIX and BSD signal routines provided by VxWorks in the kernel, see Table 4-17. Table 4-17 Basic Signal Calls POSIX 1003.1b Compatible Routine UNIX BSD Compatible Routine Description signal( ) signal( ) Specifies the handler associated with a signal. raise( ) N/A Sends a signal to yourself. sigaction( ) sigvec( ) Examines or sets the signal handler for a signal. sigsuspend( ) pause( ) Suspends a task until a signal is delivered. sigpending( ) N/A Retrieves a set of pending signals blocked from delivery. sigemptyset( ) N/A sigfillset( ) sigaddset( ) sigdelset( ) sigismember( ) Manipulates a signal mask. sigprocmask( ) N/A Sets the mask of blocked signals. sigprocmask( ) N/A Adds to a set of blocked signals. 229 VxWorks Kernel Programmer's Guide, 6.6 VxWorks also provides a POSIX and BSD-like kill( ) routine, which sends a signal to a task. VxWorks also provides additional routines that serve as aliases for POSIX routines, such as rtpKill( ), that provide for sending signals from the kernel to processes. For more information about signal routines, see the VxWorks API reference for sigLib and rtpSigLib. 4.18.3 Queued Signal Routines The sigqueue( ) family of routines provides an alternative to the kill( ) family of routines for sending signals. The important differences between the two are the following: ■ The sigqueue( ) routine includes an application-specified value that is sent as part of the signal. This value supplies whatever context is appropriate for the signal handler. This value is of type sigval (defined in signal.h); the signal handler finds it in the si_value field of one of its arguments, a structure siginfo_t. ■ The sigqueue( ) routine enables the queueing of multiple signals for any task. The kill( ) routine, by contrast, delivers only a single signal, even if multiple signals arrive before the handler runs. VxWorks includes signals reserved for application use, numbered consecutively from SIGRTMIN to SIGRTMAX. The number of signals reserved is governed by the RTSIG_MAX macro (with a value of 16), which defined in the POSIX 1003.1 standard. The signal values themselves are not specified by POSIX. For portability, specify these signals as offsets from SIGRTMIN (for example, use SIGRTMIN+2 to refer to the third reserved signal number). All signals delivered with sigqueue( ) are queued by numeric order, with lower-numbered signals queuing ahead of higher-numbered signals. POSIX 1003.1 also introduced an alternative means of receiving signals. The routine sigwaitinfo( ) differs from sigsuspend( ) or pause( ) in that it allows your application to respond to a signal without going through the mechanism of a registered signal handler: when a signal is available, sigwaitinfo( ) returns the value of that signal as a result, and does not invoke a signal handler even if one is registered. The routine sigtimedwait( ) is similar, except that it can time out. The basic queued signal routines are described in Table 4-18. For detailed information on signals, see the API reference for sigLib. 230 4 Multitasking 4.18 Signals Table 4-18 POSIX 1003.1b Queued Signal Routines Routine Description sigqueue( ) Sends a queued signal to a task. sigwaitinfo( ) Waits for a signal. sigtimedwait( ) Waits for a signal with a timeout. 4 Additional non-POSIX VxWorks queued signal routines are described in Table 4-19. These routines are provided for assisting in porting VxWorks 5.x kernel applications to processes. The POSIX routines described in Table 4-18 should be used for developing new applications that execute as real-time processes. Note that a parallel set of non-POSIX APIs are provided for the kill( ) family of POSIX routines—taskKill( ), rtpKill( ), and rtpTaskKill( ). Table 4-19 Non-POSIX Queued Signal Routines Routine Description taskSigqueue( ) Sends a queued signal from a task in a process to another task in the same process, to a public task in another process, or from a kernel task to a process task. rtpSigqueue( ) Sends a queued signal from a kernel task to a process or from a process to another process. rtpTaskSigqueue( ) Sends a queued signal from a kernel task to a specified task in a process (kernel-space only). 231 VxWorks Kernel Programmer's Guide, 6.6 Example 4-5 Queued Signals #include #include #include #include #ifdef _WRS_KERNEL #include #include #include #endif typedef void (*FPTR) (int); void sigMasterHandler ( int sig, /* caught signal */ #ifdef _WRS_KERNEL int code, #else siginfo_t * pInfo, /* signal info */ #endif struct sigcontext *pContext /* unused */ ); /**************************************************************************** * * main - entry point for the queued signal demo * * This routine acts the task entry point in the case of the demo spawned as a * kernel task. It also can act as a RTP entry point in the case of RTP based * demo. */ STATUS main (void) { sigset_t sig = sigmask (SIGUSR1); union sigval sval; struct sigaction in; sigprocmask (SIG_UNBLOCK, &sig, NULL); in.sa_handler = (FPTR) sigMasterHandler; in.sa_flags = 0; (void) sigemptyset (&in.sa_mask); if (sigaction (SIGUSR1, &in, NULL) != OK) { printf ("Unable to set up handler for task (0x%x)\n", taskIdCurrent); return (ERROR); } printf ("Task 0x%x installed signal handler for signal # %d.\ Ready for signal.\n", taskIdCurrent, SIGUSR1); 232 4 Multitasking 4.18 Signals for (;;); } /**************************************************************************** * * sigMasterHandler - signal handler * * This routine is the signal handler for the SIGUSR1 signal */ void sigMasterHandler ( int sig, /* caught signal */ #ifdef _WRS_KERNEL int code, #else siginfo_t * pInfo , /* signal info */ #endif struct sigcontext *pContext /* unused */ ) { printf ("Task 0x%x got signal # %d signal value %d \n", taskIdCurrent, sig, #ifdef _WRS_KERNEL code #else pInfo->si_value.sival_int #endif ); } /**************************************************************************** * * sig - helper routine to send a queued signal * * This routine can send a queued signal to a kernel task or RTP task or RTP. * is the ID of the receiver entity. is the value to be sent * along with the signal. The signal number being sent is SIGUSR1. */ #ifdef _WRS_KERNEL STATUS sig ( int id, int val ) { union sigval valueCode; valueCode.sival_int = val; 233 4 VxWorks Kernel Programmer's Guide, 6.6 if (TASK_ID_VERIFY (id) == OK) { if (IS_KERNEL_TASK (id)) { if (sigqueue (id, SIGUSR1, valueCode) == ERROR) { printf ("Unable to send SIGUSR1 signal to 0xx%x, errno = 0x%x\n", id, errnoGet()); return ERROR; } } else { rtpTaskSigqueue ((WIND_TCB *)id, SIGUSR1, valueCode); } } else if (OBJ_VERIFY ((RTP_ID)id, rtpClassId) != ERROR) { rtpSigqueue ((RTP_ID)id, SIGUSR1, valueCode); } else { return (ERROR); } return (OK); } #endif 234 4 Multitasking 4.18 Signals The code provided in this example can be used to do any of the following: ■ ■ ■ Send a queued signal to a kernel task. Send a queued signal to a task in a process (RTP). Send a queued signal to a process. The sig( ) routine provided in this code is a helper routine used to send a queued signal. To use the code as a kernel application, VxWorks must be configured with BUNDLE_NET_SHELL and BUNDLE_POSIX. To send a queued signal to a kernel task: 1. Build the code with the VxWorks image or as a downloadable kernel module. Boot the system. If the code is not linked to the system image, load the module; for example, from the kernel shell: -> ld < signal_ex.o value = 8382064 = 0x7fe670 2. Spawn a task with main( ) as the entry point. For example: -> sp main Task spawned: id = 0x7fd620, name = t1 value = 8377888 = 0x7fd620 -> Task 0x7fd620 installed signal handler for signal # 30. signal. sp main 3. Ready for Send a queued signal to the spawned kernel task. From the kernel shell use the command: sig kernelTaskId, signalValue For example: -> sig 0x7fd620, 20 value = 0 = 0x0 -> Task 0x7fd620 got signal # 30 sig 0x7fd620, 20 value = 0 = 0x0 -> Task 0x7fd620 got signal # 30 signal value 20 signal value 20 For information on using the code in a process (as an RTP application), see the VxWorks Application Programmer’s Guide: Multitasking. 235 4 VxWorks Kernel Programmer's Guide, 6.6 4.18.4 Signal Events The signal event facility allows a pthread or task to receive notification that a particular event has occurred (such as the arrival of a message at a message queue, or the firing of a timer) by way of a signal. The following routines can be used to register for signal notification of their respective event activities: mq_notify( ), timer_create( ), timer_open( ), aio_read( ), aio_write( ) and lio_listio( ). The POSIX 1003.1-2001 standard defines three signal event notification types: SIGEV_NONE Indicates that no notification is required when the event occurs. This is useful for applications that use asynchronous I/O with polling for completion. SIGEV_SIGNAL Indicates that a signal is generated when the event occurs. SIGEV_THREAD Provides for callback functions for asynchronous notifications done by a function call within the context of a new thread. This provides a multi-threaded process with a more natural means of notification than signals. VxWorks supports this option in user space (processes), but not in the kernel. The notification type is specified using the sigevent structure, which is defined in installDir/vxworks-6.x/target/h/sigeventCommon.h. A pointer the structure is used in the call to register for signal notification; for example, with mq_notify( ). To use the signal event facility, configure VxWorks with the INCLUDE_SIGEVENT component. 4.18.5 Signal Handlers Signals are more appropriate for error and exception handling than as a general-purpose intertask communication mechanism. And normally, signal handlers should be treated like ISRs: no routine should be called from a signal handler that might cause the handler to block. Because signals are asynchronous, it is difficult to predict which resources might be unavailable when a particular signal is raised. To be perfectly safe, call only those routines listed in Table 4-20. Deviate from this practice only if you are certain that your signal handler cannot create a deadlock situation. 236 4 Multitasking 4.18 Signals In addition, you should be particularly careful when using C++ for a signal handler or when invoking a C++ method from a signal handler written in C or assembly. Some of the issues involved in using C++ include the following: ■ Table 4-20 The VxWorks intConnect( ) and signal( ) routines require the address of the function to execute when the interrupt or signal occurs, but the address of a non-static member function cannot be used, so static member functions must be implement. ■ Objects cannot be instantiated or deleted in signal handling code. ■ C++ code used to execute in a signal handler should restrict itself to Embedded C++. No exceptions nor run-time type identification (RTTI) should be used. Routines Callable by Signal Handlers Library Routines bLib All routines errnoLib errnoGet( ), errnoSet( ) eventLib eventSend( ) fppArchLib fppSave( ), fppRestore( ) intLib intContext( ), intCount( ), intVecSet( ), intVecGet( ) intArchLib intLock( ), intUnlock( ) logLib logMsg( ) lstLib All routines except lstFree( ) mathALib All routines, if fppSave( )/fppRestore( ) are used msgQLib msgQSend( ) rngLib All routines except rngCreate( ) and rngDelete( ) semLib semGive( ) except mutual-exclusion semaphores, semFlush( ) sigLib kill( ) taskLib taskSuspend( ), taskResume( ), taskPrioritySet( ), taskPriorityGet( ), taskIdVerify( ), taskIdDefault( ), taskIsReady( ), taskIsSuspended( ), taskTcb( ) 237 4 VxWorks Kernel Programmer's Guide, 6.6 Table 4-20 Routines Callable by Signal Handlers (cont’d) Library Routines tickLib tickAnnounce( ), tickSet( ), tickGet( ) tyLib tyIRd( ), tyITx( ) vxLib vxTas( ), vxMemProbe( ) wdLib wdStart( ), wdCancel( ) Most signals are delivered asynchronously to the execution of a program. Therefore programs must be written to account for the unexpected occurrence of signals, and handle them gracefully. Unlike ISR's, signal handlers execute in the context of the interrupted task. VxWorks does not distinguish between normal task execution and a signal context, as it distinguishes between a task context and an ISR. Therefore the system has no way of distinguishing between a task execution context and a task executing a signal handler. To the system, they are the same. When you write signal handlers make sure that they: ■ Release resources prior to exiting: – – – Free any allocated memory. Close any open files. Release any mutual exclusion resources such as semaphores. ■ Leave any modified data structures in a sane state. ■ Notify the kernel with an appropriate error return value. Mutual exclusion between signal handlers and tasks must be managed with care. In general, users should avoid the following activity in signal handlers: ■ Taking mutual exclusion (such as semaphores) resources that can also be taken by any other element of the application code. This can lead to deadlock. ■ Modifying any shared data memory that may have been in the process of modification by any other element of the application code when the signal was delivered. This compromises mutual exclusion and leads to data corruption. ■ Using longjmp( ) to change the flow of task execution. If longjmp( ) is used in a signal handler to re-initialize a running task, you must ensure that the signal is not sent to the task while the task is holding a critical resource (such as a kernel mutex). For example, if a signal is sent to a task that is executing 238 4 Multitasking 4.19 Watchdog Timers malloc( ), the signal handler that calls longjmp( ) could leave the kernel in an inconsistent state. These scenarios are very difficult to debug, and should be avoided. One safe way to synchronize other elements of the application code and a signal handler is to set up dedicated flags and data structures that are set from signal handlers and read from the other elements. This ensures a consistency in usage of the data structure. In addition, the other elements of the application code must check for the occurrence of signals at any time by periodically checking to see if the synchronizing data structure or flag has been modified in the background by a signal handler, and then acting accordingly. The use of the volatile keyword is useful for memory locations that are accessed from both a signal handler and other elements of the application. Taking a mutex semaphore in a signal handler is an especially bad idea. Mutex semaphores can be taken recursively. A signal handler can therefore easily re-acquire a mutex that was taken by any other element of the application. Since the signal handler is an asynchronously executing entity, it has thereby broken the mutual exclusion that the mutex was supposed to provide. Taking a binary semaphore in a signal handler is an equally bad idea. If any other element has already taken it, the signal handler will cause the task to block on itself. This is a deadlock from which no recovery is possible. Counting semaphores, if available, suffer from the same issue as mutexes, and if unavailable, are equivalent to the binary semaphore situation that causes an unrecoverable deadlock. On a general note, the signal facility should be used only for notifying/handling exceptional or error conditions. Usage of signals as a general purpose IPC mechanism or in the data flow path of an application can cause some of the pitfalls described above. 4.19 Watchdog Timers VxWorks includes a watchdog-timer mechanism that allows any C function to be connected to a specified time delay. Watchdog timers are maintained as part of the system clock ISR. Functions invoked by watchdog timers execute as interrupt service code at the interrupt level of the system clock. Restrictions on ISRs apply to 239 4 VxWorks Kernel Programmer's Guide, 6.6 routines connected to watchdog timers. The functions in Table 4-21 are provided by the wdLib library. Table 4-21 Watchdog Timer Calls Call Description wdCreate( ) Allocates and initializes a watchdog timer. wdDelete( ) Terminates and deallocates a watchdog timer. wdStart( ) Starts a watchdog timer. wdCancel( ) Cancels a currently counting watchdog timer. A watchdog timer is first created by calling wdCreate( ). Then the timer can be started by calling wdStart( ), which takes as arguments the number of ticks to delay, the C function to call, and an argument to be passed to that function. After the specified number of ticks have elapsed, the function is called with the specified argument. The watchdog timer can be canceled any time before the delay has elapsed by calling wdCancel( ). Example 4-6 Watchdog Timers /* Creates a watchdog timer and sets it to go off in 3 seconds.*/ /* includes */ #include #include #include /* defines */ #define SECONDS (3) WDOG_ID myWatchDogId; task (void) { /* Create watchdog */ if ((myWatchDogId = wdCreate( )) == NULL) return (ERROR); /* Set timer to go off in SECONDS - printing a message to stdout */ if (wdStart (myWatchDogId, sysClkRateGet( ) * SECONDS, logMsg, "Watchdog timer just expired\n") == ERROR) return (ERROR); /* ... */ } For information about POSIX timers, see 5.6 POSIX Clocks and Timers, p.259. 240 4 Multitasking 4.20 Interrupt Service Routines 4.20 Interrupt Service Routines Hardware interrupt handling is of key significance in real-time systems, because it is usually through interrupts that the system is informed of external events. For the fastest possible response to interrupts, VxWorks runs interrupt service routines (ISRs) in a special context outside of any task’s context. Thus, interrupt handling involves no task context switch. Table 4-22 lists the interrupt routines provided in intLib and intArchLib. Table 4-22 Interrupt Routines Call Description intConnect( ) Connects a C routine to an interrupt vector. intContext( ) Returns TRUE if called from interrupt level. intCount( ) Gets the current interrupt nesting depth. intLevelSet( ) Sets the processor interrupt mask level. intLock( ) Disables interrupts. intUnlock( ) Re-enables interrupts. intVecBaseSet( ) Sets the vector base address. intVecBaseGet( ) Gets the vector base address. intVecSet( ) Sets an exception vector. intVecGet( ) Gets an exception vector. For information about interrupt locks and latency, see 4.11.1 Interrupt Locks and Latency, p.197. NOTE: The intLock( ) and intUnlock( ) routines are provided for the UP configuration of VxWorks, but not the SMP configuration. Several alternative are available for SMP systems, including the ISR-callable spinlock, which default to intLock( ) and intUnlock( ) behavior in a UP system. For more information, see 15.6.1 ISR-Callable Spinlocks, p.682 and 15.15 Migrating Code to VxWorks SMP, p.702. 241 4 VxWorks Kernel Programmer's Guide, 6.6 4.20.1 Connecting Routines to Interrupts You can use system hardware interrupts other than those used by VxWorks. VxWorks provides the routine intConnect( ), which allows C functions to be connected to any interrupt. The arguments to this routine are the byte offset of the interrupt vector to connect to, the address of the C function to be connected, and an argument to pass to the function. When an interrupt occurs with a vector established in this way, the connected C function is called at interrupt level with the specified argument. When the interrupt handling is finished, the connected function returns. A routine connected to an interrupt in this way is called an interrupt service routine (ISR). Interrupts cannot actually vector directly to C functions. Instead, intConnect( ) builds a small amount of code that saves the necessary registers, sets up a stack entry (either on a special interrupt stack, or on the current task’s stack) with the argument to be passed, and calls the connected function. On return from the function it restores the registers and stack, and exits the interrupt; see Figure 4-15. Figure 4-15 Routine Built by intConnect( ) Wrapper built by intConnect( ) save registers set up stack invoke routine restore registers and stack exit Interrupt Service Routine myISR ( int val; ) ( /* deal with hardware*/ ... ) intConnect (INUM_TO_IVEC (someIntNum), myISR, someVal); For target boards with VME backplanes, the BSP provides two standard routines for controlling VME bus interrupts, sysIntEnable( ) and sysIntDisable( ). 4.20.2 Interrupt Stack All ISRs use the same interrupt stack. This stack is allocated and initialized by the system at startup according to specified configuration parameters. It must be large enough to handle the worst possible combination of nested interrupts. 242 4 Multitasking 4.20 Interrupt Service Routines ! CAUTION: Some architectures do not permit using a separate interrupt stack, and ISRs use the stack of the interrupted task. With such architectures, make sure to create tasks with enough stack space to handle the worst possible combination of nested interrupts and the worst possible combination of ordinary nested calls. See the VxWorks reference for your BSP to determine whether your architecture supports a separate interrupt stack. If it does not, also see Task Stack Protection, p.176. Use the checkStack( ) facility during development to see how close your tasks and ISRs have come to exhausting the available stack space. In addition to experimenting with stack size, you can also configure and test systems with guard zone protection for interrupt stacks (for more information, see Interrupt Stack Protection, p.243). Filling Interrupt Stacks By default, interrupt (and task) stacks are filled with 0xEE. Filling stacks is useful during development for debugging with the checkStack( ) routine. It is generally not used in deployed systems because not filling stacks provides better performance. You can use the VX_GLOBAL_NO_STACK_FILL configuration parameter (when you configure VxWorks) to disable stack filling for all interrupts (and tasks) in the system. Interrupt Stack Protection Systems can be configured with the INCLUDE_PROTECT_INTERRUPT_STACK component to provide guard zone protection at the start and end of the interrupt stack. If the size of the system becomes an issue, the component can be removed for final testing and the deployed system. An overrun guard zone prevents a task from going beyond the end of its predefined stack size and ensures that the integrity of the system is not compromised. An under-run guard zone typically prevents buffer overflows from corrupting memory above the stack. The CPU generates an exception when a task attempts to access any of the guard zones. The size of a stack is always rounded up to a multiple the MMU page size when a guard zone is inserted. 243 4 VxWorks Kernel Programmer's Guide, 6.6 The sizes of the guard zones are defined by the following configuration parameters: ■ INTERRUPT_STACK_OVERFLOW_SIZE for interrupt stack overflow size. ■ INTERRUPT_STACK_UNDERFLOW_SIZE for interrupt stack underflow size. The value of these parameters can be modified to increase the size of the guard zone. The size of a guard zone is rounded up to the CPU MMU page size. The insertion of a guard zone can be prevented by setting the parameter to zero. 4.20.3 Writing and Debugging ISRs There are some restrictions on the routines you can call from an ISR. For example, you cannot use routines like printf( ), malloc( ), and semTake( ) in your ISR. You can, however, use semGive( ), logMsg( ), msgQSend( ), and bcopy( ). For more information, see 4.20.5 Special Limitations of ISRs, p.245. Two basic techniques for debugging an ISR are to use logMsg( ) and to have global variables that are incremented each time though the ISR. You can then print the globals from the shell. You can also use global variables from the shell to turn on different condition flows through the ISR. 4.20.4 ISRs and the Kernel Work Queue The VxWorks kernel reduces interrupt latency to a minimum by protecting portions of its critical sections using a work deferral mechanism as opposed to locking interrupts. Work deferral consists of storing kernel work requests performed by ISRs that interrupt the kernel while it is in one of its critical sections. For example, an ISR that performs a semGive( ) after having interrupted the kernel in a critical section would cause work to be stored in the work queue. This work is processed after the ISR returns and immediately after the kernel exits its critical section. This process involves a static buffer, also known as work queue, used to store work requests until they are processed. This is all internal to the VxWorks kernel and users must never make use of the work queue. However, it is possible for the work queue to overflow in situations where a large number of interrupts cause work deferral without allowing the kernel to complete execution of the critical section that was originally interrupted. These situations are uncommon and are often symptoms of ill-behaved interrupt service routines. A work queue overflow is also known as a work queue panic in reference to the message the kernel displays as a result of an overflow: 244 4 Multitasking 4.20 Interrupt Service Routines workQPanic: Kernel work queue overflow In order to help reduce the occurrences of work queue overflows, system architects can use the WIND_JOBS_MAX kernel configuration parameter to increase the size of the kernel work queue. However in most cases this is simply hiding the root cause of the overflow. 4.20.5 Special Limitations of ISRs Many VxWorks facilities are available to ISRs, but there are some important limitations. These limitations stem from the fact that an ISR does not run in a regular task context and has no task control block, so all ISRs share a single stack. For this reason, the basic restriction on ISRs is that they must not invoke routines that might cause the caller to block. For example, they must not try to take a semaphore, because if the semaphore is unavailable, the kernel tries to switch the caller to the pended state. However, ISRs can give semaphores, releasing any tasks waiting on them. Because the memory facilities malloc( ) and free( ) take a semaphore, they cannot be called by ISRs, and neither can routines that make calls to malloc( ) and free( ). For example, ISRs cannot call any creation or deletion routines. ISRs also must not perform I/O through VxWorks drivers. Although there are no inherent restrictions in the I/O system, most device drivers require a task context because they might block the caller to wait for the device. An important exception is the VxWorks pipe driver, which is designed to permit writes by ISRs. VxWorks supplies a logging facility, in which a logging task prints text messages to the system console. This mechanism was specifically designed for ISR use, and is the most common way to print messages from ISRs. For more information, see the VxWorks API reference for logLib. An ISR also must not call routines that use a floating-point coprocessor. In VxWorks, the interrupt driver code created by intConnect( ) does not save and restore floating-point registers; thus, ISRs must not include floating-point instructions. If an ISR requires floating-point instructions, it must explicitly save and restore the registers of the floating-point coprocessor using routines in fppArchLib. In addition, you should be particularly careful when using C++ for an ISR or when invoking a C++ method from an ISR written in C or assembly. Some of the issues involved in using C++ include the following: 245 4 VxWorks Kernel Programmer's Guide, 6.6 ■ The VxWorks intConnect( ) routine require the address of the function to execute when the interrupt occurs, but the address of a non-static member function cannot be used, so static member functions must be implement. ■ Objects cannot be instantiated or deleted in ISR code. ■ C++ code used to execute in an ISR should restrict itself to Embedded C++. No exceptions nor run-time type identification (RTTI) should be used. All VxWorks utility libraries, such as the linked-list and ring-buffer libraries, can be used by ISRs. As discussed earlier (4.5 Task Error Status: errno, p.184), the global variable errno is saved and restored as a part of the interrupt enter and exit code generated by the intConnect( ) facility. Thus, errno can be referenced and modified by ISRs as in any other code. Table 4-23 lists routines that can be called from ISRs. 246 4 Multitasking 4.20 Interrupt Service Routines Table 4-23 Routines Callable by ISRs Library Routine bLib All routines errnoLib errnoGet( ), errnoSet( ) eventLib eventSend( ) fppArchLib fppSave( ), fppRestore( ) intLib intContext( ), intCount( ), intVecSet( ), intVecGet( ) intArchLib intLock( ), intUnlock( ) logLib logMsg( ) lstLib All routines except lstFree( ) mathALib All routines, if fppSave( )/fppRestore( ) are used msgQLib msgQSend( ) rngLib All routines except rngCreate( ) and rngDelete( ) pipeDrv write( ) selectLib selWakeup( ), selWakeupAll( ) semLib semGive( ) except mutual-exclusion semaphores, semFlush( ) semPxLib sem_post( ) sigLib kill( ) taskLib taskSuspend( ), taskResume( ), taskPrioritySet( ), taskPriorityGet( ), taskIdVerify( ), taskIdDefault( ), taskIsReady( ), taskIsSuspended( ), taskTcb( ) tickLib tickAnnounce( ), tickSet( ), tickGet( ) tyLib tyIRd( ), tyITx( ) vxLib vxTas( ), vxMemProbe( ) wdLib wdStart( ), wdCancel( ) 4 247 VxWorks Kernel Programmer's Guide, 6.6 4.20.6 Exceptions at Interrupt Level When a task causes a hardware exception such as an illegal instruction or bus error, the task is suspended and the rest of the system continues uninterrupted. However, when an ISR causes such an exception, there is no safe recourse for the system to handle the exception. The ISR has no context that can be suspended. Instead, VxWorks stores the description of the exception in a special location in low memory and executes a system restart. The VxWorks boot loader tests for the presence of the exception description in low memory and if it is detected, display it on the system console. The boot loader’s e command re-displays the exception description; see Wind River Workbench User’s Guide: Setting up Your Hardware. One example of such an exception is the following message: workQPanic: Kernel work queue overflow. This exception usually occurs when kernel calls are made from interrupt level at a very high rate. It generally indicates a problem with clearing the interrupt signal or a similar driver problem. (See 4.20.4 ISRs and the Kernel Work Queue, p.244.) 4.20.7 Reserving High Interrupt Levels The VxWorks interrupt support described earlier in this section is acceptable for most applications. However, on occasion, low-level control is required for events such as critical motion control or system failure response. In such cases it is desirable to reserve the highest interrupt levels to ensure zero-latency response to these events. To achieve zero-latency response, VxWorks provides the routine intLockLevelSet( ), which sets the system-wide interrupt-lockout level to the specified level. If you do not specify a level, the default is the highest level supported by the processor architecture. For information about architecture-specific implementations of intLockLevelSet( ), see the VxWorks Architecture Supplement. ! CAUTION: Some hardware prevents masking certain interrupt levels; check the hardware manufacturer’s documentation. 248 4 Multitasking 4.20 Interrupt Service Routines 4.20.8 Additional Restrictions for ISRs at High Interrupt Levels ISRs connected to interrupt levels that are not locked out (either an interrupt level higher than that set by intLockLevelSet( ), or an interrupt level defined in hardware as non-maskable) have special restrictions: 4 ■ The ISR can be connected only with intVecSet( ). ■ The ISR cannot use any VxWorks operating system facilities that depend on interrupt locks for correct operation. The effective result is that the ISR cannot safely make any call to any VxWorks function, except reboot. For more information, see the VxWorks Architecture Supplement for the architecture in question. ! WARNING: The use of NMI with any VxWorks functionality, other than reboot, is not recommended. Routines marked as interrupt safe do not imply they are NMI safe and, in fact, are usually the very ones that NMI routines must not call (because they typically use intLock( ) to achieve the interrupt safe condition). 4.20.9 Interrupt-to-Task Communication While it is important that VxWorks support direct connection of ISRs that run at interrupt level, interrupt events usually propagate to task-level code. Many VxWorks facilities are not available to interrupt-level code, including I/O to any device other than pipes. The following techniques can be used to communicate from ISRs to task-level code: ■ Shared Memory and Ring Buffers ISRs can share variables, buffers, and ring buffers with task-level code. ■ Semaphores ISRs can give semaphores (except for mutual-exclusion semaphores and VxMP shared semaphores) that tasks can take and wait for. ■ Message Queues ISRs can send messages to message queues for tasks to receive (except for shared message queues using VxMP). If the queue is full, the message is discarded. 249 VxWorks Kernel Programmer's Guide, 6.6 ■ Pipes ISRs can write messages to pipes that tasks can read. Tasks and ISRs can write to the same pipes. However, if the pipe is full, the message written is discarded because the ISR cannot block. ISRs must not invoke any I/O routine on pipes other than write( ). ■ Signals ISRs can signal tasks, causing asynchronous scheduling of their signal handlers. ■ VxWorks Events ISRs can send VxWorks events to tasks. 250 5 POSIX Facilities 5.1 Introduction 252 5.2 Configuring VxWorks with POSIX Facilities 253 5.3 General POSIX Support 255 5.4 POSIX Header Files 257 5.5 POSIX Namespace 259 5.6 POSIX Clocks and Timers 259 5.7 POSIX Asynchronous I/O 263 5.8 POSIX Advisory File Locking 263 5.9 POSIX Page-Locking Interface 264 5.10 POSIX Threads 264 5.11 POSIX Thread Mutexes and Condition Variables 273 5.12 POSIX and VxWorks Scheduling 277 5.13 POSIX Semaphores 289 5.14 POSIX Message Queues 299 5.15 POSIX Signals 313 5.16 POSIX Memory Management 313 251 VxWorks Kernel Programmer's Guide, 6.6 5.1 Introduction VxWorks provides extensive POSIX support in many of its native kernel libraries. To facilitate application portability, VxWorks provides additional POSIX interfaces as optional components. In the kernel, VxWorks implements some of the traditional interfaces described by the POSIX standard IEEE Std 1003.1 (POSIX.1) as well as many of the real-time interfaces in the POSIX.1 optional functionality. For detailed information about POSIX standards and facilities, see The Open Group Web sites at http://www.opengroup.org/ and http://www.unix.org/. POSIX and Real-Time Systems While VxWorks provides many POSIX compliant APIs, not all POSIX APIs are suitable for embedded and real-time systems, or are entirely compatible with the VxWorks operating system architecture. In a few cases, therefore, Wind River has imposed minor limitations on POSIX functionality to serve either real-time systems or VxWorks compatibility. For example: ■ Swapping memory to disk is not appropriate in real-time systems, and VxWorks provides no facilities for doing so. It does, however, provide POSIX page-locking routines to facilitate porting code to VxWorks. The routines otherwise provide no useful function—pages are always locked in VxWorks systems (for more information see 5.9 POSIX Page-Locking Interface, p.264). ■ VxWorks tasks are scheduled on a system-wide basis; processes themselves cannot be scheduled. As a consequence, while POSIX access routines allow two values for contention scope (PTHREAD_SCOPE_SYSTEM and PTHREAD_SCOPE_PROCESS), only system-wide scope is implemented in VxWorks for these routines (for more information, see 5.10 POSIX Threads, p.264 and 5.12 POSIX and VxWorks Scheduling, p.277). Any such limitations on POSIX functionality are identified in this chapter, or in other chapters of this guide that provide more detailed information on specific POSIX APIs. POSIX and VxWorks Facilities This chapter describes the POSIX support provided by VxWorks and VxWorks-specific POSIX extensions. In addition, it compares native VxWorks facilities with similar POSIX facilities that are also available with VxWorks. The qualifier VxWorks is used in this chapter to identify native non-POSIX APIs for purposes of comparison with POSIX APIs. For example, you can find a discussion of VxWorks semaphores contrasted to POSIX semaphores in 5.13.1 Comparison of 252 5 POSIX Facilities 5.2 Configuring VxWorks with POSIX Facilities POSIX and VxWorks Semaphores, p.290, although POSIX semaphores are also implemented in VxWorks. VxWorks extensions to POSIX are identified as such. NOTE: This chapter provides information about POSIX facilities available in the kernel. For information about facilities available for real-time processes (RTPs), see the corresponding chapter in the VxWorks Application Programmer’s Guide. 5.2 Configuring VxWorks with POSIX Facilities VxWorks provides extensive POSIX support for the kernel with many of its libraries (see 5.3 General POSIX Support, p.255), but the default configuration of VxWorks does not include many other POSIX facilities that may be used. The optional VxWorks components that provide support for individual POSIX libraries are described in this section. General POSIX support for kernel space can be provided with the BUNDLE_POSIX component bundle. If memory constraints require a finer-grained configuration, individual components can be used for selected features. See the configuration instructions for individual POSIX features throughout this chapter for more information in this regard. ! CAUTION: The set of components used for POSIX support in kernel space is not the same as the set of components used for POSIX support in user space. For information about the components for user space, see Table 5-1, and see the VxWorks Application Programmer's Guide: POSIX Facilities for the appropriate component bundle. 5.2.1 VxWorks Components for POSIX Facilities Table 5-1 provides an overview of the individual VxWorks components that must be configured in the kernel to provide support for the specified POSIX facilities. Networking facilities are described in the Wind River Network Stack for VxWorks 6 Programmer’s Guide. 253 5 VxWorks Kernel Programmer's Guide, 6.6 Table 5-1 VxWorks Components Providing POSIX Facilities POSIX Facility Required VxWorks Component for Kernel for Processes Standard C library INCLUDE_ANSI_* components Dinkum C library (libc) Asynchronous I/O INCLUDE_POSIX_AIO, with system driver INCLUDE_POSIX_AIO_SYSDR V and INCLUDE_PIPES INCLUDE_POSIX_CLOCKS and INCLUDE_POSIX_TIMERS Clocks INCLUDE_POSIX_CLOCKS INCLUDE_POSIX_CLOCKS Directory and file utilities INCLUDE_POSIX_DIRLIB N/A ftruncate( ) INCLUDE_POSIX_FTRUNC N/A Memory locking INCLUDE_POSIX_MEM N/A Memory management N/A INCLUDE_RTP Memory-mapped files N/A INCLUDE_POSIX_MAPPED_FILES Shared memory objects N/A INCLUDE_POSIX_MAPPED_FILES and INCLUDE_POSIX_SHM Message queues INCLUDE_POSIX_MQ INCLUDE_POSIX_MQ pthreads INCLUDE_POSIX_THREADS INCLUDE_POSIX_CLOCKS, INCLUDE_POSIX_PTHREAD_SCHEDULE, and INCLUDE_PTHREAD_CPUTIME Process Scheduling INCLUDE_POSIX_SCHED API N/A Semaphores INCLUDE_POSIX_SEM INCLUDE_POSIX_SEM Signals INCLUDE_POSIX_SIGNALS N/A Timers INCLUDE_POSIX_TIMERS INCLUDE_POSIX_TIMERS Trace N/A INCLUDE_POSIX_TRACE 254 5 POSIX Facilities 5.3 General POSIX Support Table 5-1 VxWorks Components Providing POSIX Facilities (cont’d) POSIX Facility POSIX PSE52 support Required VxWorks Component for Kernel for Processes N/A BUNDLE_RTP_POSIX_PSE52 5 5.3 General POSIX Support Many POSIX-compliant libraries are provided for VxWorks. These libraries are listed in Table 5-2; see the API references for these libraries for detailed information. 255 VxWorks Kernel Programmer's Guide, 6.6 Table 5-2 POSIX Libraries Functionality Library Asynchronous I/O aioPxLib Buffer manipulation bLib Clock facility clockLib Directory handling dirLib Environment handling C Library File duplication iosLib File management fsPxLib and ioLib I/O functions ioLib Options handling getopt POSIX message queues mqPxLib POSIX semaphores semPxLib POSIX timers timerLib POSIX threads pthreadLib Standard I/O and some ANSI C Library Math C Library Memory allocation memLib and memPartLib Network/Socket APIs network libraries String manipulation C Library Trace facility pxTraceLib The following sections of this chapter describe the optional POSIX API components that are provided in addition to the native VxWorks APIs. 256 5 POSIX Facilities 5.4 POSIX Header Files ! CAUTION: Wind River advises that you do not use both POSIX libraries and native VxWorks libraries that provide similar functionality. Doing so may result in undesirable interactions between the two, as some POSIX APIs manipulate resources that are also used by native VxWorks APIs. For example, do not use tickLib routines to manipulate the system's tick counter if you are also using clockLib routines, do not use the taskLib API to change the priority of a POSIX thread instead of the pthread API, and so on. Checking for POSIX Support at Run-time A POSIX application can use the following APIs at run-time to determine the status of POSIX support in the system: ■ The sysconf( ) routine returns the current values of the configurable system variables, allowing an application to determine whether an optional feature is supported or not, and the precise value of system's limits. ■ The confstr( ) routine returns a string associated with a system variable. With this release, the confstr( ) routine returns a string only for the system's default path. ■ The uname( ) routine lets an application get information about the system on which it is running. The identification information provided for VxWorks is the system name (VxWorks), the network name of the system, the system's release number, the machine name (BSP model), the architecture's endianness, the kernel version number, the processor name (CPU family), the BSP revision level, and the system's build date. 5.4 POSIX Header Files The POSIX 1003.1 standard defines a set of header files as part of the application development environment. The VxWorks user-side development environment provides more POSIX header files than the kernel’s, and their content is also more in agreement with the POSIX standard than the kernel header files. The POSIX header files available for the kernel development environment are listed in Table 5-3. 257 5 VxWorks Kernel Programmer's Guide, 6.6 Table 5-3 POSIX Header Files Header File Description aio.h asynchronous input and output assert.h verify program assertion ctype.h character types dirent.h format of directory entries errno.h system error numbers fcntl.h file control options limits.h implementation-defined constants locale.h category macros math.h mathematical declarations mqueue.h message queues pthread.h pthreads sched.h execution scheduling semaphore.h semaphores setjmp.h stack environment declarations signal.h signals stdio.h standard buffered input/output stdlib.h standard library definitions string.h string operations sys/mman.h memory management declarations sys/resource.h definitions for XSI resource operations sys/stat.h data returned by the stat( ) function sys/types.h data types sys/un.h definitions for UNIX domain sockets 258 5 POSIX Facilities 5.5 POSIX Namespace Table 5-3 POSIX Header Files (cont’d) Header File Description time.h time types trace.h trace facility unistd.h standard symbolic constants and types utime.h access and modification times structure 5 5.5 POSIX Namespace POSIX namespace isolation can be provided for user-mode (RTP) applications. For information in this regard, see the VxWorks Application Programmer’s Guide: POSIX Facilities. 5.6 POSIX Clocks and Timers VxWorks provides POSIX 1003.1b standard clock and timer interfaces. POSIX Clocks POSIX defines various software (virtual) clocks, which are identified as the CLOCK_REALTIME clock, CLOCK_MONOTONIC clock, process CPU-time clocks, and thread CPU-time clocks. These clocks all use one system hardware timer. The real-time clock and the monotonic clock are system-wide clocks, and are therefore supported for both the VxWorks kernel and processes. The process CPU-time clocks are not supported in VxWorks. The thread CPU-time clocks are supported for POSIX threads running in processes. A POSIX thread can use the real-time clock, the monotonic clock, and a thread CPU-time clock for its application. 259 VxWorks Kernel Programmer's Guide, 6.6 For information about thread CPU-time clocks, see the VxWorks Application Programmer’s Guide: POSIX Facilities. The real-time clock can be reset (but only from the kernel). The monotonic clock cannot be reset, and provides the time that has elapsed since the system booted. The real-time clock can be accessed with the POSIX clock and timer routines by using the clock_id parameter CLOCK_REALTIME. A real-time clock can be reset at run time with a call to clock_settime( ) from within the kernel (not from a process). The monotonic clock can be accessed by calling clock_gettime( ) with a clock_id parameter of CLOCK_MONOTONIC. A monotonic clock keeps track of the time that has elapsed since system startup; that is, the value returned by clock_gettime( ) is the amount of time (in seconds and nanoseconds) that has passed since the system booted. A monotonic clock cannot be reset. Applications can therefore rely on the fact that any measurement of a time interval that they might make has not been falsified by a call to clock_settime( ). Both CLOCK_REALTIME and CLOCK_MONOTONIC are defined in time.h. See Table 5-4 for a list of the POSIX clock routines. The obsolete VxWorks-specific POSIX extension clock_setres( ) is provided for backwards-compatibility purposes. For more information about clock routines, see the API reference for clockLib. Table 5-4 POSIX Clock Routines Routine clock_getres( ) Description Get the clock resolution (CLOCK_REALTIME and CLOCK_MONOTONIC). clock_setres( ) Set the clock resolution. Obsolete VxWorks-specific POSIX extension. clock_gettime( ) Get the current clock time (CLOCK_REALTIME and CLOCK_MONOTONIC). clock_settime( ) Set the clock to a specified time for CLOCK_REALTIME (fails for CLOCK_MONOTONIC; not supported for a thread CPU-time clock in the kernel). To include the clockLib library in the system, configure VxWorks with the INCLUDE_POSIX_CLOCKS component. For thread CPU-time clocks, the INCLUDE_POSIX_PTHREAD_SCHEDULER and INCLUDE_POSIX_THREAD_CPUTIME components must be used as well. 260 5 POSIX Facilities 5.6 POSIX Clocks and Timers POSIX Timers The POSIX timer facility provides routines for tasks to signal themselves at some time in the future. Routines are provided to create, set, and delete a timer. Timers are created based on clocks. In the kernel, the CLOCK_REALTIME and CLOCK_MONOTONIC clocks are supported for timers. In processes, the CLOCK_REALTIME clock, CLOCK_MONOTONIC clock, and thread CPU-time clocks (including CLOCK_THREAD_CPUTIME_ID clock) are supported. When a timer goes off, the default signal, SIGALRM, is sent to the task. To install a signal handler that executes when the timer expires, use the sigaction( ) routine (see 4.18 Signals, p.226). See Table 5-5 for a list of the POSIX timer routines. The VxWorks timerLib library includes a set of VxWorks-specific POSIX extensions: timer_open( ), timer_close( ), timer_cancel( ), timer_connect( ), and timer_unlink( ). These routines allow for an easier and more powerful use of POSIX timers on VxWorks. For more information, see the VxWorks API reference for timerLib. Table 5-5 POSIX Timer Routines Routine Description timer_create( ) Allocate a timer using the specified clock for a timing base (CLOCK_REALTIME or CLOCK_MONOTONIC). timer_delete( ) Remove a previously created timer. timer_open( ) Open a named timer. VxWorks-specific POSIX extension. timer_close( ) Close a named timer. VxWorks-specific POSIX extension. timer_gettime( ) Get the remaining time before expiration and the reload value. timer_getoverrun( ) Return the timer expiration overrun. timer_settime( ) Set the time until the next expiration and arm timer. timer_cancel( ) Cancel a timer. VxWorks-specific POSIX extension. 261 5 VxWorks Kernel Programmer's Guide, 6.6 Table 5-5 Example 5-1 POSIX Timer Routines (cont’d) Routine Description timer_connect( ) Connect a user routine to the timer signal. VxWorks-specific POSIX extension. timer_unlink( ) Unlink a named timer. VxWorks-specific POSIX extension. nanosleep( ) Suspend the current pthread (task) until the time interval elapses. sleep( ) Delay for a specified amount of time. alarm( ) Set an alarm clock for delivery of a signal. POSIX Timers /* This example creates a new timer and stores it in timerid. */ /* includes */ #include #include int createTimer (void) { timer_t timerid; /* create timer */ if (timer_create (CLOCK_REALTIME, NULL, &timerid) == ERROR) { printf ("create FAILED\n"); return (ERROR); } return (OK); } The POSIX nanosleep( ) routine provides specification of sleep or delay time in units of seconds and nanoseconds, in contrast to the ticks used by the VxWorks taskDelay( ) function. Nevertheless, the precision of both is the same, and is determined by the system clock rate; only the units differ. To include the timerLib library in a system, configure VxWorks with the INCLUDE_POSIX_TIMERS component. 262 5 POSIX Facilities 5.7 POSIX Asynchronous I/O 5.7 POSIX Asynchronous I/O POSIX asynchronous I/O (AIO) routines are provided by the aioPxLib library. The VxWorks AIO implementation meets the specification of the POSIX 1003.1 standard. For more information, see 7.7 Asynchronous Input/Output, p.381. 5 5.8 POSIX Advisory File Locking POSIX advisory file locking provides byte-range locks on POSIX-conforming files (for VxWorks, this means files in an HRFS file system). The VxWorks implementation meets the specification of the POSIX 1003.1 standard. POSIX advisory file locking is provided through the fcntl( ) file control function. To include POSIX advisory file locking facilities in VxWorks, configure the system with the INCLUDE_POSIX_ADVISORY_FILE_LOCKING component. The VxWorks implementation of advisory file locking involves a behavioral difference with regard to deadlock detection because VxWorks processes are not scheduled. Note that this distinction only matters if you have multiple pthreads (or tasks) within one process (RTP). According to POSIX, advisory locks are identified by a process ID, and when a process exits all of its advisory locks are destroyed, which is true for VxWorks. But because VxWorks processes cannot themselves be scheduled, individual advisory locks on a given byte range of a file have two owners: the pthread (or task) that actually holds the lock, and the process that contains the pthread. In addition, the calculation of whether one lock would deadlock another lock is done on a pthread basis, rather than a process basis. This means that deadlocks are detected if the pthread requesting a new lock would block on any pthread (in any given process) that is currently blocked (whether directly or indirectly) on any advisory lock that is held by the requesting pthread. Immediate-blocking detection (F_SETLK requests) always fail immediately if the requested byte range cannot be locked without waiting for some other lock, regardless of the identity of the owner of that lock. 263 VxWorks Kernel Programmer's Guide, 6.6 5.9 POSIX Page-Locking Interface The real-time extensions of the POSIX 1003.1 standard are used with operating systems that perform paging and swapping. On such systems, applications that attempt real-time performance can use the POSIX page-locking facilities to protect certain blocks of memory from paging and swapping. VxWorks does not support memory paging and swapping because the serious delays in execution time that they cause are undesirable in a real-time system. However, page-locking routines can be included in VxWorks to facilitate porting POSIX applications to VxWorks. These routines do not perform any function, as all pages are always kept in memory. The POSIX page-locking routines are part of the memory management library, mmanPxLib, and are listed in Table 5-6. Table 5-6 POSIX Page-Locking Routines Routine Purpose on Systems with Paging or Swapping mlockall( ) Locks into memory all pages used by a task. munlockall( ) Unlocks all pages used by a task. mlock( ) Locks a specified page. munlock( ) Unlocks a specified page. To include the mmanPxLib library in the system, configure VxWorks with the INCLUDE_POSIX_MEM component. 5.10 POSIX Threads POSIX threads (also known as pthreads) are similar to VxWorks tasks, but with additional characteristics. In VxWorks pthreads are implemented on top of native tasks, but maintain pthread IDs that differ from the IDs of the underlying tasks. The main reasons for including POSIX thread support in VxWorks are the following: 264 5 POSIX Facilities 5.10 POSIX Threads ■ For porting POSIX applications to VxWorks. ■ To make use of the POSIX thread scheduler in real-time processes (including concurrent scheduling policies). For information about POSIX thread scheduler, see 5.12 POSIX and VxWorks Scheduling, p.277. 5 5.10.1 POSIX Thread Attributes A major difference between VxWorks tasks and POSIX threads is the way in which options and settings are specified. For VxWorks tasks these options are set with the task creation API, usually taskSpawn( ). POSIX threads, on the other hand, have characteristics that are called attributes. Each attribute contains a set of values, and a set of access routines to retrieve and set those values. You specify all pthread attributes before pthread creation in the attributes object pthread_attr_t. In a few cases, you can dynamically modify the attribute values of a pthread after its creation. 5.10.2 VxWorks-Specific Pthread Attributes The VxWorks implementation of POSIX threads provides two additional pthread attributes (which are POSIX extensions)—pthread name and pthread options—as well as routines for accessing them. Pthread Name While POSIX threads are not named entities, the VxWorks tasks upon which they are based are named. By default the underlying task elements are named pthrNumber (for example, pthr3). The number part of the name is incremented each time a new thread is created (with a roll-over at 2^32 - 1). It is, however, possible to name these tasks using the thread name attribute. ■ Attribute Name: threadname ■ Possible Values: a null-terminated string of characters ■ Default Value: none (the default naming policy is used) ■ Access Functions (VxWorks-specific POSIX extensions): pthread_attr_setname( ) and pthread_attr_getname( ) 265 VxWorks Kernel Programmer's Guide, 6.6 Pthread Options POSIX threads are agnostic with regard to target architecture. Some VxWorks tasks, on the other hand, may be created with specific options in order to benefit from certain features of the architecture. For example, for the Altivec-capable PowerPC architecture, tasks must be created with the VX_ALTIVEC_TASK in order to make use of the Altivec processor. The pthread options attribute can be used to set such options for the VxWorks task upon which the POSIX thread is based. ■ Attribute Name: threadoptions ■ Possible Values: the same as the VxWorks task options. See taskLib.h ■ Default Value: none (the default task options are used) ■ Access Functions (VxWorks-specific POSIX extensions): pthread_attr_setopt( ) and pthread_attr_getopt( ) 5.10.3 Specifying Attributes when Creating Pthreads The following examples create a pthread using the default attributes and use explicit attributes. Example 5-2 Creating a pthread Using Explicit Scheduling Attributes pthread_t tid; pthread_attr_t attr; int ret; pthread_attr_init(&attr); /* set the inheritsched attribute to explicit */ pthread_attr_setinheritsched(&attr, PTHREAD_EXPLICIT_SCHED); /* set the schedpolicy attribute to SCHED_FIFO */ pthread_attr_setschedpolicy(&attr, SCHED_FIFO); /* create the pthread */ ret = pthread_create(&tid, &attr, entryFunction, entryArg); 266 5 POSIX Facilities 5.10 POSIX Threads Example 5-3 Creating a pthread Using Default Attributes pthread_t tid; int ret; /* create the pthread with NULL attributes to designate default values */ ret = pthread_create(&tid, NULL, entryFunction, entryArg); Example 5-4 Designating Your Own Stack for a pthread 5 pthread_t threadId; pthread_attr_t attr; void * stackaddr = NULL; int stacksize = 0; /* initialize the thread's attributes */ pthread_attr_init (&attr); /* * Allocate memory for a stack region for the thread. Malloc() is used * for simplification since a real-life case is likely to use memPartAlloc() * on the kernel side, or mmap() on the user side. */ stacksize = 2 * 4096 /* let's allocate two pages */ stackaddr = malloc (stacksize); if (stackbase == NULL) { printf ("FAILED: mystack: malloc failed\n"); return (-1); } /* set the stackaddr attribute */ pthread_attr_setstackaddr (&attr, stackaddr); /* set the stacksize attribute */ pthread_attr_setstacksize (&attr, stacksize); /* set the schedpolicy attribute to SCHED_FIFO */ pthread_attr_setschedpolicy (&attr, SCHED_FIFO); /* create the pthread */ ret = pthread_create (&threadId, &attr, mystack_thread, 0); 267 VxWorks Kernel Programmer's Guide, 6.6 5.10.4 POSIX Thread Creation and Management VxWorks provides many POSIX thread routines. Table 5-7 lists a few that are directly relevant to pthread creation or execution. See the VxWorks API reference for information about the other routines, and more details about all of them. Table 5-7 POSIX Thread Routines Routine Description pthread_create( ) Create a pthread. pthread_cancel( ) Cancel the execution of a pthread pthread_detach( ) Detach a running pthread so that it cannot be joined by another pthread. pthread_join( ) Wait for a pthread to terminate. pthread_getschedparam( ) Dynamically set value of scheduling priority attribute. pthread_setschedparam( ) Dynamically set scheduling priority and policy parameter. sched_get_priority_max( ) Get the maximum priority that a pthread can get. sched_get_priority_min( ) Get the minimum priority that a pthread can get. sched_rr_get_interval( ) Get the time quantum of execution of the round-robin policy. sched_yield( ) Relinquishes the CPU. 268 5 POSIX Facilities 5.10 POSIX Threads 5.10.5 POSIX Thread Attribute Access The POSIX attribute-access routines are described in Table 5-8. The VxWorks-specific POSIX extension routines are described in section 5.10.2 VxWorks-Specific Pthread Attributes, p.265. Table 5-8 POSIX Thread Attribute-Access Routines 5 Routine Description pthread_attr_getstacksize( ) Get value of the stack size attribute. pthread_attr_setstacksize( ) Set the stack size attribute. pthread_attr_getstackaddr( ) Get value of stack address attribute. pthread_attr_setstackaddr( ) Set value of stack address attribute. pthread_attr_getdetachstate( ) Get value of detachstate attribute (joinable or detached). pthread_attr_setdetachstate( ) Set value of detachstate attribute (joinable or detached). pthread_attr_getscope( ) Get contention scope. Only PTHREAD_SCOPE_SYSTEM is supported for VxWorks. pthread_attr_setscope( ) Set contention scope. Only PTHREAD_SCOPE_SYSTEM is supported for VxWorks. pthread_attr_getinheritsched( ) Get value of scheduling-inheritance attribute. pthread_attr_setinheritsched( ) Set value of scheduling-inheritance attribute. pthread_attr_getschedpolicy( ) Get value of the scheduling-policy attribute (which is not used by default). pthread_attr_setschedpolicy( ) Set scheduling-policy attribute (which is not used by default). pthread_attr_getschedparam( ) Get value of scheduling priority attribute. pthread_attr_setschedparam( ) Set scheduling priority attribute. 269 VxWorks Kernel Programmer's Guide, 6.6 Table 5-8 POSIX Thread Attribute-Access Routines (cont’d) Routine Description pthread_attr_getopt( ) Get the task options applying to the pthread. VxWorks-specific POSIX extension. pthread_attr_setopt( ) Set non-default task options for the pthread. VxWorks-specific POSIX extension. pthread_attr_getname( ) Get the name of the pthread. VxWorks-specific POSIX extension. pthread_attr_setname( ) Set a non-default name for the pthread. VxWorks-specific POSIX extension. 5.10.6 POSIX Thread Private Data POSIX threads can store and access private data; that is, pthread-specific data. They use a key maintained for each pthread by the pthread library to access that data. A key corresponds to a location associated with the data. It is created by calling pthread_key_create( ) and released by calling pthread_key_delete( ). The location is accessed by calling pthread_getspecific( ) and pthread_setspecific( ). This location represents a pointer to the data, and not the data itself, so there is no limitation on the size and content of the data associated with a key. The pthread library supports a maximum of 256 keys for all the pthreads in the kernel. The pthread_key_create( ) routine has an option for a destructor function, which is called when the creating pthread exits or is cancelled, if the value associated with the key is non-NULL. This destructor function frees the storage associated with the data itself, and not with the key. It is important to set a destructor function for preventing memory leaks to occur when the pthread that allocated memory for the data is cancelled. The key itself should be freed as well, by calling pthread_key_delete( ), otherwise the key cannot be reused by the pthread library. 5.10.7 POSIX Thread Cancellation POSIX provides a mechanism, called cancellation, to terminate a pthread gracefully. There are two types of cancellation: deferred and asynchronous. 270 5 POSIX Facilities 5.10 POSIX Threads Deferred cancellation causes the pthread to explicitly check to see if it was cancelled. This happens in one of the two following ways: ■ ■ The code of the pthread executes calls to pthread_testcancel( ) at regular intervals. The pthread calls a function that contains a cancellation point during which the pthread may be automatically cancelled. Asynchronous cancellation causes the execution of the pthread to be forcefully interrupted and a handler to be called, much like a signal.1 Automatic cancellation points are library routines that can block the execution of the pthread for a lengthy period of time. NOTE: While the msync( ), fcntl( ), and tcdrain( ) routines are mandated POSIX 1003.1 cancellation points, they are not provided with VxWorks for this release. The POSIX cancellation points provided in VxWorks libraries are described in Table 5-9. 1. Asynchronous cancellation is actually implemented with a special signal, SIGCNCL, which users should be careful not to block or to ignore. 271 5 VxWorks Kernel Programmer's Guide, 6.6 Table 5-9 Pthread Cancellation Points in VxWorks Libraries Library Routines aioPxLib aio_suspend( ) ioLib creat( ), open( ), read( ), write( ), close( ), fsync( ), fdatasync( ) mqPxLib mq_receive( ), mq_send( ) pthreadLib pthread_cond_timedwait( ), pthread_cond_wait( ), pthread_join( ), pthread_testcancel( ) semPxLib sem_wait( ) sigLib pause( ), sigsuspend( ), sigtimedwait( ), sigwait( ), sigwaitinfo( ) timerLib sleep( ), nanosleep( ) Routines that can be used with cancellation points of pthreads are listed in Table 5-10. Table 5-10 Pthread Cancellation Routines Routine Description pthread_cancel( ) Cancel execution of a pthread. pthread_testcancel( ) Create a cancellation point in the calling pthread. pthread_setcancelstate( ) Enables or disables cancellation. pthread_setcanceltype( ) Selects deferred or asynchronous cancellation. pthread_cleanup_push( ) Registers a function to be called when the pthread is cancelled, exits, or calls pthread_cleanup_pop( ) with a non-null run parameter. pthread_cleanup_pop( ) Unregisters a function previously registered with pthread_cleanup_push( ). This function is immediately executed if the run parameter is non-null. 272 5 POSIX Facilities 5.11 POSIX Thread Mutexes and Condition Variables 5.11 POSIX Thread Mutexes and Condition Variables Pthread mutexes (mutual exclusion variables) and condition variables provide compliance with the POSIX 1003.1c standard. Like POSIX threads, mutexes and condition variables have attributes associated with them. Mutex attributes are held in a data type called pthread_mutexattr_t, which contains two attributes, protocol and prioceiling. The routines used to manage these attributes are described below. For more information about these and other mutex routines, see the API reference for pthreadLib. 5.11.1 Thread Mutexes The routines that can be used to act directly on a mutex object and on the mutex attribute object are listed in Table 5-11 and Table 5-12 (respectively). Table 5-11 POSIX Routines Acting on a Mutex Object Routine Description pthread_mutex_destroy( ) Destroy a mutex. pthread_mutex_init( ) Initialize a mutex. pthread_mutex_getprioceiling( ) Get the priority ceiling of a mutex. pthread_mutex_setprioceiling( ) Set the priority ceiling of a mutex. pthread_mutex_lock( ) Lock a mutex. pthread_mutex_trylock( ) Check and lock a mutex if available. pthread_mutex_unlock( ) Unlock a mutex. 273 5 VxWorks Kernel Programmer's Guide, 6.6 Table 5-12 POSIX Routines Acting on a Mutex Attribute Object Routine Description pthread_mutexattr_init( ) Initialize mutex attributes object. pthread_mutexattr_destroy( ) Destroy mutex attributes object. pthread_mutexattr_getprioceiling( ) Get prioceiling attribute of mutex attributes object. pthread_mutexattr_setprioceiling( ) Set prioceiling attribute of mutex attributes object. pthread_mutexattr_getprotocol( ) Get protocol attribute of mutex attributes object. pthread_mutexattr_setprotocol( ) Set protocol attribute of mutex attributes object. Protocol Mutex Attribute The protocol mutex attribute defines how the mutex variable deals with the priority inversion problem (which is described in the section for VxWorks mutual-exclusion semaphores; see 4.12.3 Mutual-Exclusion Semaphores, p.205). ■ Attribute Name: protocol ■ Possible Values: PTHREAD_PRIO_NONE, PTHREAD_PRIO_INHERIT and PTHREAD_PRIO_PROTECT ■ Access Routines: pthread_mutexattr_getprotocol( ) and pthread_mutexattr_setprotocol( ) The PTHREAD_PRIO_INHERIT option is the default value of the protocol attribute for pthreads created in the kernel (unlike pthreads created in processes, for which the default is PTHREAD_PRIO_NONE). The PTHREAD_PRIO_INHERIT value is used to create a mutex with priority inheritance—and is equivalent to the association of SEM_Q_PRIORITY and SEM_INVERSION_SAFE options used with semMCreate( ). A pthread owning a mutex variable created with the PTHREAD_PRIO_INHERIT value inherits the priority of any higher-priority pthread waiting for the mutex and executes at this elevated priority until it releases the mutex, at which points it returns to its original priority. 274 5 POSIX Facilities 5.11 POSIX Thread Mutexes and Condition Variables Because it might not be desirable to elevate a lower-priority pthread to a priority above a certain level, POSIX defines the notion of priority ceiling, described below. Mutual-exclusion variables created with priority protection use the PTHREAD_PRIO_PROTECT value. Priority Ceiling Mutex Attribute 5 The prioceiling attribute is the POSIX priority ceiling for mutex variables created with the protocol attribute set to PTHREAD_PRIO_PROTECT. ■ Attribute Name: prioceiling ■ Possible Values: any valid (POSIX) priority value (0-255, with zero being the lowest). ■ Access Routines: pthread_mutexattr_getprioceiling( ) and pthread_mutexattr_setprioceiling( ) ■ Dynamic Access Routines: pthread_mutex_getprioceiling( ) and pthread_mutex_setprioceiling( ) Note that the POSIX priority numbering scheme is the inverse of the VxWorks scheme. For more information see 5.12.2 POSIX and VxWorks Priority Numbering, p.279. A priority ceiling is defined by the following conditions: ■ Any pthread attempting to acquire a mutex, whose priority is higher than the ceiling, cannot acquire the mutex. ■ Any pthread whose priority is lower than the ceiling value has its priority elevated to the ceiling value for the duration that the mutex is held. ■ The pthread’s priority is restored to its previous value when the mutex is released. 5.11.2 Condition Variables A pthread condition variable corresponds to an object that permits pthreads to synchronize on an event or state represented by the value of a variable. This is a more complicated type of synchronization than the one allowed by mutexes only. Its main advantage is that is allows for passive waiting (as opposed to active waiting or polling) on a change in the value of the variable. Condition variables are used in conjunction with mutexes (one mutex per condition variable). The routines 275 VxWorks Kernel Programmer's Guide, 6.6 that can be used to act directly on a condition variable and on the condition variable attribute object are listed in Table 5-11 and Table 5-12 (respectively). Table 5-13 Table 5-14 POSIX Routines Acting on a Condition Variable Object Routine Description pthread_cond_destroy( ) Destroy condition variables. pthread_cond_init( ) Initialize condition variables. pthread_cond_broadcast( ) Broadcast a condition. pthread_cond_signal( ) Signal a condition. pthread_cond_wait( ) Wait on a condition. pthread_cond_timedwait( ) Wait on a condition with timeout. POSIX Routines Acting on a Condition Variable Attribute Object Routine Description pthread_condattr_destroy( ) Destroy condition variable attributes object. pthread_condattr_init( ) Initialize condition variable attributes object. 276 5 POSIX Facilities 5.12 POSIX and VxWorks Scheduling 5.12 POSIX and VxWorks Scheduling VxWorks can be configured with either the traditional (native) VxWorks scheduler or with a POSIX thread scheduler. Neither can be used to schedule processes (RTPs). The only entities that can be scheduled in VxWorks are tasks and pthreads. The VxWorks implementation of a POSIX thread scheduler is an enhancement of the traditional VxWorks scheduler that provides additional scheduling facilities for pthreads running in processes. With either scheduler, VxWorks tasks and pthreads share a single priority range and the same global scheduling scheme. With the POSIX thread scheduler, however, pthreads running in processes may have individual (concurrent) scheduling policies. Note that VxWorks must be configured with the POSIX thread scheduler in order to run pthreads in processes. NOTE: Wind River recommends that you do not use both POSIX APIs and VxWorks APIs in the same application. Doing so may make a POSIX application non-compliant. Table 5-15 provides an overview of how scheduling works for tasks and pthreads, for each of the schedulers, in both the kernel and processes (RTPs). The key differences are the following: ■ The POSIX thread scheduler provides POSIX scheduling support for threads running in processes. ■ In all other cases, the POSIX thread scheduler schedules pthreads and tasks in the same (non-POSIX) manner as the traditional VxWorks scheduler. (There is a minor difference between how it handles tasks and pthreads whose priorities have been lowered; see Differences in Re-Queuing Pthreads and Tasks With Lowered Priorities, p.285.) ■ The traditional VxWorks scheduler cannot be used to schedule pthreads in processes. In fact, pthreads cannot be started in processes unless VxWorks is configured with the POSIX thread scheduler. The information provided in Table 5-15 is discussed in detail in subsequent sections. 277 5 VxWorks Kernel Programmer's Guide, 6.6 Table 5-15 Task and Pthread Scheduling in the Kernel and in Processes POSIX Thread Scheduler Execution Environment Kernel Processes Tasks Pthreads Priority-based preemptive, or round-robin scheduling. Same as task scheduling. Priority-based preemptive, or round robin scheduling. POSIX FIFO, round-robin, sporadic, or other (system default). No concurrent scheduling policies. Concurrent scheduling policies available. Traditional VxWorks Scheduler Tasks Pthreads Priority-based preemptive, or round-robin scheduling. Same as task scheduling. Priority-based preemptive, or round-robin scheduling. N/A. No concurrent scheduling policies. Pthreads cannot be run in processes with traditional VxWorks scheduler.a a. The traditional VxWorks scheduler cannot ensure behavioral compliance with the POSIX 1 standard. 278 5 POSIX Facilities 5.12 POSIX and VxWorks Scheduling 5.12.1 Differences in POSIX and VxWorks Scheduling In general, the POSIX scheduling model and scheduling in a VxWorks system differ in the following ways—regardless of whether the system is configured with the Wind River POSIX thread scheduler or the traditional VxWorks scheduler: ■ POSIX supports a two-level scheduling model that includes the concept of contention scope, by which the scheduling of pthreads can apply system wide or on a process basis. In VxWorks, on the other hand, processes (RTPs) cannot themselves be scheduled, and tasks and pthreads are scheduled on a system-wide (kernel and processes) basis. ■ POSIX applies scheduling policies on a process-by-process and thread-by-thread basis. VxWorks applies scheduling policies on a system-wide basis, for all tasks and pthreads, whether in the kernel or in processes. This means that all tasks and pthreads use either a preemptive priority scheme or a round-robin scheme. The only exception to this rule is that pthreads executing in processes can be subject to concurrent (individual) scheduling policies, including sporadic scheduling (note that the POSIX thread scheduler must be used in this case). ■ POSIX supports the concept of scheduling allocation domain; that is, the association between processes or threads and processors. Since VxWorks does not support multi-processor hardware, there is only one domain on VxWorks and all the tasks and pthreads are associated to it. ■ The POSIX priority numbering scheme is the inverse of the VxWorks scheme. For more information see 5.12.2 POSIX and VxWorks Priority Numbering, p.279. ■ VxWorks does not support the POSIX thread-concurrency feature, as all threads are scheduled. The POSIX thread-concurrency APIs are provided for application portability, but they have no effect. 5.12.2 POSIX and VxWorks Priority Numbering The POSIX priority numbering scheme is the inverse of the VxWorks priority numbering scheme. In POSIX, the higher the number, the higher the priority. In VxWorks, the lower the number, the higher the priority, where 0 is the highest priority. The priority numbers used with the POSIX scheduling library, schedPxLib, do not, therefore, match those used and reported by all other components of VxWorks. You can change the default POSIX numbering scheme by setting the global variable posixPriorityNumbering to FALSE. If you do so, schedPxLib uses the 279 5 VxWorks Kernel Programmer's Guide, 6.6 VxWorks numbering scheme (a smaller number means a higher priority) and its priority numbers match those used by the other components of VxWorks. In the following sections, discussions of pthreads and tasks at the same priority level refer to functionally equivalent priority levels, and not to priority numbers. 5.12.3 Default Scheduling Policy All VxWorks tasks and pthreads are scheduled according to the system-wide default scheduling policy. The only exception to this rule is for pthreads running in user mode (in processes). In this case, concurrent scheduling policies that differ from the system default can be applied to pthreads. Note that pthreads can be run in processes only if VxWorks is configured with the POSIX thread scheduler; they cannot be run in processes if VxWorks is configured with the traditional scheduler. The system-wide default scheduling policy for VxWorks, regardless of which scheduler is used, is priority-based preemptive scheduling—which corresponds to the POSIX SCHED_FIFO scheduling policy. At run-time the active system-wide default scheduling policy can be changed to round-robin scheduling with the kernelTimeSlice( ) routine. It can be changed back by calling kernelTimeSlice( ) with a parameter of zero. VxWorks round-robin scheduling corresponds to the POSIX SCHED_RR policy. The kernelTimeSlice( ) routine cannot be called in user mode (that is, from a process). A call with a non-zero parameter immediately affects all kernel and user tasks, all kernel pthreads, and all user pthreads using the SCHED_OTHER policy. Any user pthreads running with the SCHED_RR policy are unaffected by the call; but those started after it use the newly defined timeslice. 280 5 POSIX Facilities 5.12 POSIX and VxWorks Scheduling 5.12.4 VxWorks Traditional Scheduler The VxWorks traditional scheduler can be used with both tasks and pthreads in the kernel. It cannot be used with pthreads in processes. If VxWorks is configured with the traditional scheduler, a pthread_create( ) call in a process fails and the errno is set to ENOSYS. The traditional VxWorks scheduler schedules pthreads as if they were tasks. All tasks and pthreads executing in a system are therefore subject to the current default scheduling policy (either the priority-based preemptive policy or the round-robin scheduling policy; see 5.12.3 Default Scheduling Policy, p.280), and concurrent policies cannot be applied to individual pthreads. For general information about the traditional scheduler and how it works with tasks, see 4.3 Task Scheduling, p.166. The scheduling options provided by the traditional VxWorks scheduler are similar to the POSIX ones. The following pthreads scheduling policies correspond to the traditional VxWorks scheduling policies: ■ SCHED_FIFO is similar to VxWorks priority-based preemptive scheduling. There are differences as to where tasks or pthreads are placed in the ready queue if their priority is lowered; see Caveats About Scheduling Behavior with the POSIX Thread Scheduler, p.284. ■ SCHED_RR corresponds to VxWorks round-robin scheduling. ■ SCHED_OTHER corresponds to the current system-wide default scheduling policy. The SCHED_OTHER policy is the default policy for pthreads in VxWorks. There is no VxWorks traditional scheduler policy that corresponds to SCHED_SPORADIC. Configuring VxWorks with the Traditional Scheduler VxWorks is configured with the traditional scheduler by default. This scheduler is provided by the INCLUDE_VX_TRADITIONAL_SCHEDULER component. Caveats About Scheduling Behavior with the VxWorks Traditional Scheduler Concurrent scheduling policies are not supported for pthreads in the kernel, and care must therefore be taken with pthread scheduling-inheritance and scheduling policy attributes. If the scheduling-inheritance attribute is set to PTHREAD_EXPLICIT_SCHED and the scheduling policy to SCHED_FIFO or SCHED_RR, and this policy does not 281 5 VxWorks Kernel Programmer's Guide, 6.6 match the current system-wide default scheduling policy, the creation of pthreads fails. Wind River therefore recommends that you always use PTHREAD_INHERIT_SCHED (which is the default) as a scheduling-inheritance attribute. In this case the current VxWorks scheduling policy applies, and the parent pthread's priority is used. Or, if the pthread must be started with a different priority than its parent, the scheduling-inheritance attribute can be set to PTHREAD_EXPLICIT_SCHED and the scheduling policy attribute set to be SCHED_OTHER (which corresponds to the current system-wide default scheduling policy.). In order to take advantage of the POSIX scheduling model, VxWorks must be configured with the POSIX thread scheduler, and the pthreads in question must be run in processes (RTPs). See 5.12.5 POSIX Threads Scheduler, p.282. 5.12.5 POSIX Threads Scheduler The POSIX thread scheduler can be used to schedule both pthreads and tasks in a VxWorks system. Note that the purpose of the POSIX thread scheduler is to provide POSIX scheduling support for pthreads running in processes. There is no reason to use it in a system that does not require this support (kernel-only systems, or systems with processes but without pthreads). The POSIX thread scheduler is required for running pthreads in processes, where it provides compliance with POSIX 1003.1 for pthread scheduling (including concurrent scheduling policies). If VxWorks is not configured with the POSIX thread scheduler, pthreads cannot be created in processes. NOTE: The POSIX priority numbering scheme is the inverse of the VxWorks scheme, so references to a given priority level or same level in comparisons of these schemes refer to functionally equivalent priority levels, and not to priority numbers. For more information about the numbering schemes see 5.12.2 POSIX and VxWorks Priority Numbering, p.279. Scheduling in the Kernel The POSIX thread scheduler schedules kernel tasks and kernel pthreads in the same manner as the traditional VxWorks task scheduler. See 4.3 Task Scheduling, p.166 for information about the traditional scheduler and how it works with VxWorks tasks, and 5.12.4 VxWorks Traditional Scheduler, p.281 for information about how 282 5 POSIX Facilities 5.12 POSIX and VxWorks Scheduling POSIX scheduling policies correspond to the traditional VxWorks scheduling policies. Scheduling in Processes When VxWorks is configured with the POSIX thread scheduler, tasks executing in processes are scheduled according to system-wide default scheduling policy. On the other hand, pthreads executing in processes are scheduled according to POSIX 1003.1. Scheduling policies can be assigned to each pthread and changed dynamically. The scheduling policies are as follows: ■ SCHED_FIFO is a preemptive priority scheduling policy. For a given priority level, pthreads scheduled with this policy are handled as peers of the VxWorks tasks at the same level. There is a slight difference in how pthreads and tasks are handled if their priorities are lowered (for more information; see Differences in Re-Queuing Pthreads and Tasks With Lowered Priorities, p.285). ■ SCHED_RR is a per-priority round-robin scheduling policy. For a given priority level, all pthreads scheduled with this policy are given the same time of execution (time-slice) before giving up the CPU. ■ SCHED_SPORADIC is a policy used for aperiodic activities, which ensures that the pthreads associated with the policy are served periodically at a high priority for a bounded amount of time, and a low background priority at all other times. ■ SCHED_OTHER corresponds to the scheduling policy currently in use for VxWorks tasks, which is either preemptive priority or round-robin. Pthreads scheduled with this policy are submitted to the system's global scheduling policy, exactly like VxWorks tasks or kernel pthreads. Note the following with regard to the VxWorks implementation of the SCHED_SPORADIC policy: ■ The system periodic clock is used for time accounting. ■ Dynamically changing the scheduling policy to SCHED_SPORADIC is not supported; however, dynamically changing the policy from SCHED_SPORADIC to another policy is supported. ■ VxWorks does not impose an upper limit on the maximum number of replenishment events with the SS_REPL_MAX macro. A default of 40 events is set with the sched_ss_max_repl field of the thread attribute structure, which can be changed. 283 5 VxWorks Kernel Programmer's Guide, 6.6 Configuring VxWorks with the POSIX Thread Scheduler To configure VxWorks with the POSIX thread scheduler, add the INCLUDE_POSIX_PTHREAD_SCHEDULER component to the kernel. Note that only the SCHED_FIFO, SCHED_RR, and SCHED_OTHER scheduling policies are provided with the INCLUDE_POSIX_PTHREAD_SCHEDULER component. For the SCHED_SPORADIC scheduling policy, the INCLUDE_PX_SCHED_SPORADIC_POLICY component must be included as well. The bundle BUNDLE_RTP_POSIX_PSE52 includes the INCLUDE_PX_SCHED_SPORADIC_POLICY component as well as the INCLUDE_POSIX_PTHREAD_SCHEDULER component. The configuration parameter POSIX_PTHREAD_RR_TIMESLICE may be used to configure the default time slicing interval for pthreads started with the SCHED_RR policy. To modify the time slice at run time, call kernelTimeSlice( ) with a different time slice value. The new time slice value only affects pthreads created after the kernelTimeSlice( ) call. NOTE: The INCLUDE_POSIX_PTHREAD_SCHEDULER component is a standalone component. It is not dependent on any other POSIX components nor is it automatically included with any other components. The POSIX thread scheduler must be added explicitly with either the INCLUDE_POSIX_PTHREAD_SCHEDULER component or the BUNDLE_RTP_POSIX_PSE52 bundle. The POSIX thread scheduler component is independent because it is intended to be used only with pthreads in processes; kernel-only systems that use pthreads, have no need to change from the default VxWorks traditional scheduler. Caveats About Scheduling Behavior with the POSIX Thread Scheduler Using the POSIX thread scheduler involves a few complexities that should be taken into account when designing your system. Care should be taken with regard to the following: ■ Using both round-robin and priority-based preemptive scheduling policies. ■ Running pthreads with the individual SCHED_OTHER policy. ■ Differences in re-queuing pthreads and tasks with lowered priorities. ■ Backwards compatibility issues for POSIX applications designed for the VxWorks traditional scheduler. 284 5 POSIX Facilities 5.12 POSIX and VxWorks Scheduling Using both Round-Robin and Priority-Based Preemptive Policies Using a combination of round-robin and priority-based preemptive policies for tasks and pthreads of the same priority level can lead to task or pthread CPU starvation for the entities running with the round-robin policy. When VxWorks is running with round-robin scheduling as the system default, tasks may not run with their expected time slice if there are pthreads running at the same priority level with the concurrent (individual) SCHED_FIFO policy. This is because one of the pthreads may monopolize the CPU and starve the tasks. Even if the usurper pthread is preempted, it stays at the head of its priority lists (as POSIX mandates), and continues to monopolize the CPU when that priority level can run again. Pthreads scheduled with the SCHED_RR or SCHED_OTHER policy are at the same disadvantage as the tasks scheduled with the round-robin policy. Similarly, when VxWorks is running with preemptive scheduling as the system default, tasks may starve pthreads with the same priority level if the latter have the concurrent (individual) SCHED_RR policy. Running pthreads with the Concurrent SCHED_OTHER Policy Pthreads created with the concurrent (individual) SCHED_OTHER policy behave the same as the system-wide default scheduling policy, which means that: ■ If the system default is currently priority-based preemptive scheduling, the SCHED_OTHER pthreads run with the preemptive policy. ■ If the system default is currently round-robin scheduling, the SCHED_OTHER pthreads run with the round-robin policy. While changing the default system policy from priority-based preemptive scheduling to round-robin scheduling (or the opposite) changes the effective scheduling policy for pthreads created with SCHED_OTHER, it has no effect on pthreads created with SCHED_RR or SCHED_FIFO. Differences in Re-Queuing Pthreads and Tasks With Lowered Priorities The POSIX thread scheduler re-queues pthreads that have had their priority lowered differently than it re-queues tasks that have had their priority lowered. The difference is as follows: ■ When the priority of a pthread is lowered (with the pthread_setschedprio( ) routine), the POSIX thread scheduler places it at the head of the priority list. ■ When the priority of a task is lowered (with the taskPrioritySet( ) routine), the POSIX thread scheduler places it at the tail of the priority list—which is the same as what the traditional VxWorks scheduler would do. 285 5 VxWorks Kernel Programmer's Guide, 6.6 What this means is that lowering the priority of a task and a pthread may have a different effect on when they will run (if there are other tasks or pthreads in their priority list). For example, if a task and a pthread each have their priority lowered to effectively the same level, the pthread will be at the head of the priority list and the task at the end. The pthread will run before any other pthreads or tasks at this level, and the task after any other pthreads or tasks. Backwards Compatibility Issues for Applications Using the POSIX thread scheduler changes the behavior of POSIX applications that were written to run with the traditional VxWorks scheduler. For existing POSIX applications that require backward-compatibility, the scheduling policy can be changed to SCHED_OTHER for all pthreads. This causes their policy to default to the active VxWorks task scheduling policy (as was the case before the introduction of the POSIX thread scheduler). 5.12.6 POSIX Scheduling Routines The POSIX 1003.1b scheduling routines provided by the schedPxLib library for VxWorks are described in Table 5-16. Table 5-16 POSIX Scheduling Routines Routine Description sched_get_priority_max( ) Gets the maximum pthread priority. sched_get_priority_min( ) Gets the minimum pthread priority. sched_rr_get_interval( ) If round-robin scheduling is in effect, gets the time slice length. sched_yield( ) Relinquishes the CPU. For more information about these routines, see the schedPxLib API reference. 286 5 POSIX Facilities 5.12 POSIX and VxWorks Scheduling NOTE: Several scheduling routines that were provided with schedPxLib for VxWorks 5.x and early versions of VxWorks 6.x are not POSIX compliant, and are maintained only for backward compatibility in the kernel. The use of these routines is deprecated: sched_setparam( ), sched_getparam( ), sched_setscheduler( ), and sched_getscheduler( ). The native VxWorks routines taskPrioritySet( ) and taskPriorityGet( ) should be used for task priorities. The POSIX routines pthread_setschedparam( ) and pthread_getschedparam( ) should be used for pthread priorities. For information about changing the default system scheduling policy, see 5.12.3 Default Scheduling Policy, p.280. For information about concurrent scheduling policies, see 5.12.5 POSIX Threads Scheduler, p.282. Note that the POSIX priority numbering scheme is the inverse of the VxWorks scheme. For more information see 5.12.2 POSIX and VxWorks Priority Numbering, p.279. To include the schedPxLib library in the system, configure VxWorks with the INCLUDE_POSIX_SCHED component. 5.12.7 Getting Scheduling Parameters: Priority Limits and Time Slice The routines sched_get_priority_max( ) and sched_get_priority_min( ) return the maximum and minimum possible POSIX priority, respectively. If round-robin scheduling is enabled, you can use sched_rr_get_interval( ) to determine the length of the current time-slice interval. This routine takes as an argument a pointer to a timespec structure (defined in time.h), and writes the number of seconds and nanoseconds per time slice to the appropriate elements of that structure. 287 5 VxWorks Kernel Programmer's Guide, 6.6 Example 5-5 Getting the POSIX Round-Robin Time Slice /* The following example checks that round-robin scheduling is enabled, * gets the length of the time slice, and then displays the time slice. */ /* includes */ #include #include STATUS rrgetintervalTest (void) { struct timespec slice; /* turn on round robin */ kernelTimeSlice (30); if (sched_rr_get_interval (0, &slice) == ERROR) { printf ("get-interval test failed\n"); return (ERROR); } printf ("time slice is %l seconds and %l nanoseconds\n", slice.tv_sec, slice.tv_nsec); return (OK); } 288 5 POSIX Facilities 5.13 POSIX Semaphores 5.13 POSIX Semaphores POSIX defines both named and unnamed semaphores, which have the same properties, but which use slightly different interfaces. The POSIX semaphore library provides routines for creating, opening, and destroying both named and unnamed semaphores. When opening a named semaphore, you assign a symbolic name,2 which the other named-semaphore routines accept as an argument. The POSIX semaphore routines provided by semPxLib are shown in Table 5-17. Table 5-17 POSIX Semaphore Routines Routine Description sem_init( ) Initializes an unnamed semaphore. sem_destroy( ) Destroys an unnamed semaphore. sem_open( ) Initializes/opens a named semaphore. sem_close( ) Closes a named semaphore. sem_unlink( ) Removes a named semaphore. sem_wait( ) Lock a semaphore. sem_trywait( ) Lock a semaphore only if it is not already locked. sem_post( ) Unlock a semaphore. sem_getvalue( ) Get the value of a semaphore. sem_timedwait( ) Lock a semaphore with a timeout. To include the POSIX semPxLib library semaphore routines in the system, configure VxWorks with the INCLUDE_POSIX_SEM component. 2. Some operating systems, such as UNIX, require symbolic names for objects that are to be shared among processes. This is because processes do not normally share memory in such operating systems. In VxWorks, named semaphores can be used to share semaphores between real-time processes. In the VxWorks kernel there is no need for named semaphores, because all kernel objects have unique identifiers. However, using named semaphores of the POSIX variety provides a convenient way of determining the object’s ID. 289 5 VxWorks Kernel Programmer's Guide, 6.6 VxWorks also provides semPxLibInit( ), a non-POSIX (kernel-only) routine that initializes the kernel’s POSIX semaphore library. It is called by default at boot time when POSIX semaphores have been included in the VxWorks configuration. 5.13.1 Comparison of POSIX and VxWorks Semaphores POSIX semaphores are counting semaphores; that is, they keep track of the number of times they are given. The VxWorks semaphore mechanism is similar to that specified by POSIX, except that VxWorks semaphores offer these additional features: ■ ■ ■ ■ ■ ■ priority inheritance task-deletion safety the ability for a single task to take a semaphore multiple times ownership of mutual-exclusion semaphores semaphore timeouts queuing mechanism options When these features are important, VxWorks semaphores are preferable to POSIX semaphores. (For information about these features, see 4. Multitasking.) The POSIX terms wait (or lock) and post (or unlock) correspond to the VxWorks terms take and give, respectively. The POSIX routines for locking, unlocking, and getting the value of semaphores are used for both named and unnamed semaphores. The routines sem_init( ) and sem_destroy( ) are used for initializing and destroying unnamed semaphores only. The sem_destroy( ) call terminates an unnamed semaphore and deallocates all associated memory. The routines sem_open( ), sem_unlink( ), and sem_close( ) are for opening and closing (destroying) named semaphores only. The combination of sem_close( ) and sem_unlink( ) has the same effect for named semaphores as sem_destroy( ) does for unnamed semaphores. That is, it terminates the semaphore and deallocates the associated memory. ! WARNING: When deleting semaphores, particularly mutual-exclusion semaphores, avoid deleting a semaphore still required by another task. Do not delete a semaphore unless the deleting task first succeeds in locking that semaphore. Similarly for named semaphores, close semaphores only from the same task that opens them. 290 5 POSIX Facilities 5.13 POSIX Semaphores 5.13.2 Using Unnamed Semaphores When using unnamed semaphores, typically one task allocates memory for the semaphore and initializes it. A semaphore is represented with the data structure sem_t, defined in semaphore.h. The semaphore initialization routine, sem_init( ), lets you specify the initial value. Once the semaphore is initialized, any task can use the semaphore by locking it with sem_wait( ) (blocking) or sem_trywait( ) (non-blocking), and unlocking it with sem_post( ). Semaphores can be used for both synchronization and exclusion. Thus, when a semaphore is used for synchronization, it is typically initialized to zero (locked). The task waiting to be synchronized blocks on a sem_wait( ). The task doing the synchronizing unlocks the semaphore using sem_post( ). If the task that is blocked on the semaphore is the only one waiting for that semaphore, the task unblocks and becomes ready to run. If other tasks are blocked on the semaphore, the task with the highest priority is unblocked. When a semaphore is used for mutual exclusion, it is typically initialized to a value greater than zero, meaning that the resource is available. Therefore, the first task to lock the semaphore does so without blocking, setting the semaphore to 0 (locked). Subsequent tasks will block until the semaphore is released. As with the previous scenario, when the semaphore is released the task with the highest priority is unblocked. 291 5 VxWorks Kernel Programmer's Guide, 6.6 Example 5-6 POSIX Unnamed Semaphores /* * This example uses unnamed semaphores to synchronize an action between the * calling task and a task that it spawns (tSyncTask). To run from the shell, * spawn as a task: * * -> sp unnameSem */ /* includes */ #include #include /* forward declarations */ void syncTask (sem_t * pSem); /************************************************************************ * unnameSem - test case for unamed semaphores * * This routine tests unamed semaphores. * * RETURNS: N/A * * ERRNOS: N/A */ void unnameSem (void) { sem_t * pSem; /* reserve memory for semaphore */ pSem = (sem_t *) malloc (sizeof (sem_t)); if (pSem == NULL) { printf ("pSem allocation failed\n"); return; } /* initialize semaphore to unavailable */ if (sem_init (pSem, 0, 0) == -1) { printf ("unnameSem: sem_init failed\n"); free ((char *) pSem); return; } /* create sync task */ printf ("unnameSem: spawning task...\n"); 292 5 POSIX Facilities 5.13 POSIX Semaphores if (taskSpawn ("tSyncTask", 90, 0, 2000, syncTask, pSem) == ERROR) { printf ("Failed to spawn tSyncTask\n"); sem_destroy (pSem); free ((char *) pSem); return; } /* do something useful to synchronize with syncTask */ /* unlock sem */ printf ("unnameSem: posting semaphore - synchronizing action\n"); if (sem_post (pSem) == -1) { printf ("unnameSem: posting semaphore failed\n"); sem_destroy (pSem); free ((char *) pSem); return; } /* all done - destroy semaphore */ if (sem_destroy (pSem) == -1) { printf ("unnameSem: sem_destroy failed\n"); return; } free ((char *) pSem); } void syncTask ( sem_t * pSem ) { /* wait for synchronization from unnameSem */ if (sem_wait (pSem) == -1) { printf ("syncTask: sem_wait failed \n"); return; } else printf ("syncTask: sem locked; doing sync’ed action...\n"); /* do something useful here */ } 293 5 VxWorks Kernel Programmer's Guide, 6.6 5.13.3 Using Named Semaphores The sem_open( ) routine either opens a named semaphore that already exists or, as an option, creates a new semaphore. You can specify which of these possibilities you want by combining the following flag values: O_CREAT Create the semaphore if it does not already exist. If it exists, either fail or open the semaphore, depending on whether O_EXCL is specified. O_EXCL Open the semaphore only if newly created; fail if the semaphore exists. The results, based on the flags and whether the semaphore accessed already exists, are shown in Table 5-18. Table 5-18 Possible Outcomes of Calling sem_open( ) Flag Settings If Semaphore Exists If Semaphore Does Not Exist None Semaphore is opened. Routine fails. O_CREAT Semaphore is opened. Semaphore is created. O_CREAT and O_EXCL Routine fails. Semaphore is created. O_EXCL Routine fails. Routine fails. Once initialized, a semaphore remains usable until explicitly destroyed. Tasks can explicitly mark a semaphore for destruction at any time, but the system only destroys the semaphore when no task has the semaphore open. If VxWorks is configured with INCLUDE_POSIX_SEM_SHOW, you can use show( ) from the shell (with the C interpreter) to display information about a POSIX semaphore. 3 3. The show( ) routine is not a POSIX routine, nor is it meant to be used programmatically. It is designed for interactive use with the shell (with the shell’s C interpreter). 294 5 POSIX Facilities 5.13 POSIX Semaphores This example shows information about the POSIX semaphore mySem with two tasks blocked and waiting for it: -> show semId value = 0 = 0x0 Semaphore name sem_open() count Semaphore value No. of blocked tasks :mySem :3 :0 :2 5 Note that show( ) takes the semaphore ID as the argument. For a group of collaborating tasks to use a named semaphore, one of the tasks first creates and initializes the semaphore, by calling sem_open( ) with the O_CREAT flag. Any task that must use the semaphore thereafter, opens it by calling sem_open( ) with the same name, but without setting O_CREAT. Any task that has opened the semaphore can use it by locking it with sem_wait( ) (blocking) or sem_trywait( ) (non-blocking), and then unlocking it with sem_post( ) when the task is finished with the semaphore. To remove a semaphore, all tasks using it must first close it with sem_close( ), and one of the tasks must also unlink it. Unlinking a semaphore with sem_unlink( ) removes the semaphore name from the name table. After the name is removed from the name table, tasks that currently have the semaphore open can still use it, but no new tasks can open this semaphore. If a task tries to open the semaphore without the O_CREAT flag, the operation fails. An unlinked semaphore is deleted by the system when the last task closes it. NOTE: POSIX named semaphores may be shared between processes only if their names start with a / (forward slash) character. They are otherwise private to the process in which they were created, and cannot be accessed from another process. See 4.9 Public and Private Objects, p.194. 295 VxWorks Kernel Programmer's Guide, 6.6 Example 5-7 POSIX Named Semaphores /* * In this example, nameSem() creates a task for synchronization. The * new task, tSyncSemTask, blocks on the semaphore created in nameSem(). * Once the synchronization takes place, both tasks close the semaphore, * and nameSem() unlinks it. To run this task from the shell, spawn * nameSem as a task: * -> sp nameSem, "myTest" */ /* includes */ #include #include #include #include #include /* forward declaration */ void syncSemTask (char * name); /**************************************************************************** * * nameSem - test program for POSIX semaphores * * This routine opens a named semaphore and spawns a task, tSyncSemTask, which * waits on the named semaphore. * * RETURNS: N/A * * ERRNO: N/A */ void nameSem ( char * name ) { sem_t * semId; /* create a named semaphore, initialize to 0*/ printf ("nameSem: creating semaphore\n"); if ((semId = sem_open (name, O_CREAT, 0, 0)) == (sem_t *) -1) { printf ("nameSem: sem_open failed\n"); return; } printf ("nameSem: spawning sync task\n"); if (taskSpawn ("tSyncSemTask", 90, 0, 4000, (FUNCPTR) syncSemTask, (int) name, 0, 0, 0, 0, 0, 0, 0, 0, 0) == ERROR) { printf ("nameSem: unable to spawn tSyncSemTask\n"); sem_close(semId); 296 5 POSIX Facilities 5.13 POSIX Semaphores return; } /* do something useful to synchronize with syncSemTask */ /* give semaphore */ printf ("nameSem: posting semaphore - synchronizing action\n"); if (sem_post (semId) == -1) { printf ("nameSem: sem_post failed\n"); sem_close(semId); return; } /* all done */ if (sem_close (semId) == -1) { printf ("nameSem: sem_close failed\n"); return; } if (sem_unlink (name) == -1) { printf ("nameSem: sem_unlink failed\n"); return; } printf ("nameSem: closed and unlinked semaphore\n"); } /**************************************************************************** * * syncSemTask - waits on a named POSIX semaphore * * This routine waits on the named semaphore created by nameSem(). * * RETURNS: N/A * * ERRNO: N/A */ void syncSemTask ( char * name ) { sem_t * semId; /* open semaphore */ printf ("syncSemTask: opening semaphore\n"); if ((semId = sem_open (name, 0)) == (sem_t *) -1) { printf ("syncSemTask: sem_open failed\n"); return; } 297 5 VxWorks Kernel Programmer's Guide, 6.6 /* block waiting for synchronization from nameSem */ printf ("syncSemTask: attempting to take semaphore...\n"); if (sem_wait (semId) == -1) { printf ("syncSemTask: taking sem failed\n"); return; } printf ("syncSemTask: has semaphore, doing sync'ed action ...\n"); /* do something useful here */ if (sem_close (semId) == -1) { printf ("syncSemTask: sem_close failed\n"); return; } } 298 5 POSIX Facilities 5.14 POSIX Message Queues 5.14 POSIX Message Queues The POSIX message queue routines, provided by mqPxLib, are shown in Table 5-19. Table 5-19 POSIX Message Queue Routines 5 Routine Description mq_open( ) Opens a message queue. mq_close( ) Closes a message queue. mq_unlink( ) Removes a message queue. mq_send( ) Sends a message to a queue. mq_receive( ) Gets a message from a queue. mq_notify( ) Signals a task that a message is waiting on a queue. mq_setattr( ) Sets a queue attribute. mq_getattr( ) Gets a queue attribute. mq_timedsend( ) Sends a message to a queue, with a timeout. mq_timedreceive( ) Gets a message from a queue, with a timeout. Note that there are behavioral differences between the kernel and user space versions of mq_open( ). The kernel version allows for creation of a message queue for any permission specified by the oflags parameter. The user-space version complies with the POSIX PSE52 profile, so that after the first call, any subsequent calls in the same process are only allowed if an equivalent or lower permission is specified. For information about the use of permissions with the user-space version of mq_open( ), see the VxWorks Application Programmer’s Guide: POSIX Facilities. The VxWorks initialization routine mqPxLibInit( ) initializes the kernel’s POSIX message queue library (this is a kernel-only routine). It is called automatically at boot time when the INCLUDE_POSIX_MQ component is part of the system. For information about the VxWorks message queue library, see the msgQLib API reference. 299 VxWorks Kernel Programmer's Guide, 6.6 5.14.1 Comparison of POSIX and VxWorks Message Queues POSIX message queues are similar to VxWorks message queues, except that POSIX message queues provide messages with a range of priorities. The differences are summarized in Table 5-20. Table 5-20 Message Queue Feature Comparison Feature VxWorks Message Queues POSIX Message Queues Maximum Message Queue Levels 1 (specified by 32 (specified by MSG_PRI_NORMAL | M SG_PRI_URGENT) MAX_PRIO_MAX) Blocked Message Queues FIFO or priority-based Priority-based Received with Timeout msgQReceive( ) option mq_timedreceive( ) (user-space only) Task Notification With VxWorks message queue events mq_notify( ) Close/Unlink Semantics With msgQOpen library Yes Send with Timeout msgQsend( ) option mq_timesend( ) (user-space only) 5.14.2 POSIX Message Queue Attributes A POSIX message queue has the following attributes: ■ an optional O_NONBLOCK flag, which prevents a mq_receive( ) call from being a blocking call if the message queue is empty ■ the maximum number of messages in the message queue ■ the maximum message size ■ the number of messages currently on the queue Tasks can set or clear the O_NONBLOCK flag using mq_setattr( ), and get the values of all the attributes using mq_getattr( ). (As allowed by POSIX, this implementation of message queues makes use of a number of internal flags that are not public.) 300 5 POSIX Facilities 5.14 POSIX Message Queues Example 5-8 Setting and Getting Message Queue Attributes /* * This example sets the O_NONBLOCK flag and examines message queue * attributes. */ /* includes */ #include #include #include #include /* defines */ #define MSG_SIZE 16 int attrEx ( char * name ) { mqd_t struct mq_attr struct mq_attr char int mqPXId; attr; oldAttr; buffer[MSG_SIZE]; prio; 5 /* mq descriptor */ /* queue attribute structure */ /* old queue attributes */ /* create read write queue that is blocking */ attr.mq_flags = 0; attr.mq_maxmsg = 1; attr.mq_msgsize = 16; if ((mqPXId = mq_open (name, O_CREAT | O_RDWR , 0, &attr)) == (mqd_t) -1) return (ERROR); else printf ("mq_open with non-block succeeded\n"); /* change attributes on queue - turn on non-blocking */ attr.mq_flags = O_NONBLOCK; if (mq_setattr (mqPXId, &attr, &oldAttr) == -1) return (ERROR); else { /* paranoia check - oldAttr should not include non-blocking. */ if (oldAttr.mq_flags & O_NONBLOCK) return (ERROR); else printf ("mq_setattr turning on non-blocking succeeded\n"); } 301 VxWorks Kernel Programmer's Guide, 6.6 /* try receiving - there are no messages but this shouldn't block */ if (mq_receive (mqPXId, buffer, MSG_SIZE, &prio) == -1) { if (errno != EAGAIN) return (ERROR); else printf ("mq_receive with non-blocking didn’t block on empty queue\n"); } else return (ERROR); /* use mq_getattr to verify success */ if (mq_getattr (mqPXId, &oldAttr) == -1) return (ERROR); else { /* test that we got the values we think we should */ if (!(oldAttr.mq_flags & O_NONBLOCK) || (oldAttr.mq_curmsgs != 0)) return (ERROR); else printf ("queue attributes are:\n\tblocking is %s\n\t message size is: %d\n\t max messages in queue: %d\n\t no. of current msgs in queue: %d\n", oldAttr.mq_flags & O_NONBLOCK ? "on" : "off", oldAttr.mq_msgsize, oldAttr.mq_maxmsg, oldAttr.mq_curmsgs); } /* clean up - close and unlink mq */ if (mq_unlink (name) == -1) return (ERROR); if (mq_close (mqPXId) == -1) return (ERROR); return (OK); } 302 5 POSIX Facilities 5.14 POSIX Message Queues 5.14.3 Displaying Message Queue Attributes The mqPxShow( ) routine can be used to display information about POSIX message queues, as illustrated below. -> mq_open ("mymq4", 0x4201, 0) value = 8380448 = 0x7fe020 -> mqPxShow 0x7fe020 Message queue name : mymq4 No. of messages in queue : 0 Maximum no. of messages : 16 Maximum message size : 16 Flags : O_WRONLY 5 O_NONBLOCK (0x4001 ) 5.14.4 Communicating Through a Message Queue Before a set of tasks can communicate through a POSIX message queue, one of the tasks must create the message queue by calling mq_open( ) with the O_CREAT flag set. Once a message queue is created, other tasks can open that queue by name to send and receive messages on it. Only the first task opens the queue with the O_CREAT flag; subsequent tasks can open the queue for receiving only (O_RDONLY), sending only (O_WRONLY), or both sending and receiving (O_RDWR). To put messages on a queue, use mq_send( ). If a task attempts to put a message on the queue when the queue is full, the task blocks until some other task reads a message from the queue, making space available. To avoid blocking on mq_send( ), set O_NONBLOCK when you open the message queue. In that case, when the queue is full, mq_send( ) returns -1 and sets errno to EAGAIN instead of pending, allowing you to try again or take other action as appropriate. One of the arguments to mq_send( ) specifies a message priority. Priorities range from 0 (lowest priority) to 31 (highest priority). When a task receives a message using mq_receive( ), the task receives the highest-priority message currently on the queue. Among multiple messages with the same priority, the first message placed on the queue is the first received (FIFO order). If the queue is empty, the task blocks until a message is placed on the queue. To avoid pending (blocking) on mq_receive( ), open the message queue with O_NONBLOCK; in that case, when a task attempts to read from an empty queue, mq_receive( ) returns -1 and sets errno to EAGAIN. To close a message queue, call mq_close( ). Closing the queue does not destroy it, but only asserts that your task is no longer using the queue. To request that the 303 VxWorks Kernel Programmer's Guide, 6.6 queue be destroyed, call mq_unlink( ). Unlinking a message queue does not destroy the queue immediately, but it does prevent any further tasks from opening that queue, by removing the queue name from the name table. Tasks that currently have the queue open can continue to use it. When the last task closes an unlinked queue, the queue is destroyed. NOTE: In VxWorks, a POSIX message queue whose name does not start with a forward-slash (/) character is considered private to the process that has opened it and can not be accessed from another process. A message queue whose name starts with a forward-slash (/) character is a public object, and other processes can access it (as according to the POSIX standard). See 4.9 Public and Private Objects, p.194. 304 5 POSIX Facilities 5.14 POSIX Message Queues Example 5-9 POSIX Message Queues /* * In this example, the mqExInit() routine spawns two tasks that * communicate using the message queue. * To run this test case on the target shell: * * -> sp mqExInit */ /* mqEx.h - message example header */ /* defines */ #define MQ_NAME "exampleMessageQueue" /* forward declarations */ void receiveTask (void); void sendTask (void); /* testMQ.c - example using POSIX message queues */ /* includes */ #include #include #include #include #include #include #include /* defines */ #define HI_PRIO 31 #define MSG_SIZE 16 #define MSG "greetings" /**************************************************************************** * * mqExInit - main for message queue send and receive test case * * This routine spawns to tasks to perform the message queue send and receive * test case. * * RETURNS: OK, or ERROR * * ERRNOS: N/A */ 305 5 VxWorks Kernel Programmer's Guide, 6.6 int mqExInit (void) { /* create two tasks */ if (taskSpawn ("tRcvTask", 151, 0, 4000, (FUNCPTR) receiveTask, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0) == ERROR) { printf ("taskSpawn of tRcvTask failed\n"); return (ERROR); } if (taskSpawn ("tSndTask", 152, 0, 4000, (FUNCPTR) sendTask, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0) == ERROR) { printf ("taskSpawn of tSendTask failed\n"); return (ERROR); } return (OK); } /**************************************************************************** * * receiveTask - receive messages from the message queue * * This routine creates a message queue and calls mq_receive() to wait for * a message arriving in the message queue. * * RETURNS: OK, or ERROR * * ERRNOS: N/A */ void receiveTask (void) { mqd_t mqPXId; /* msg queue descriptor */ char msg[MSG_SIZE]; /* msg buffer */ int prio; /* priority of message */ /* open message queue using default attributes */ if ((mqPXId = mq_open (MQ_NAME, O_RDWR | O_CREAT, 0, NULL)) == (mqd_t) -1) { printf ("receiveTask: mq_open failed\n"); return; } /* try reading from queue */ if (mq_receive (mqPXId, msg, MSG_SIZE, &prio) == -1) { printf ("receiveTask: mq_receive failed\n"); return; } else 306 5 POSIX Facilities 5.14 POSIX Message Queues { printf ("receiveTask: Msg of priority %d received:\n\t\t%s\n", prio, msg); } } /**************************************************************************** * * sendTask - send a message to a message queue * * This routine opens an already created message queue and * calls mq_send() to send a message to the opened message queue. * * RETURNS: OK, or ERROR * * ERRNOS: N/A */ void sendTask (void) { mqd_t mqPXId; /* msg queue descriptor */ /* open msg queue; should already exist with default attributes */ if ((mqPXId = mq_open (MQ_NAME, O_RDWR, 0, NULL)) == (mqd_t) -1) { printf ("sendTask: mq_open failed\n"); return; } /* try writing to queue */ if (mq_send (mqPXId, MSG, sizeof (MSG), HI_PRIO) == -1) { printf ("sendTask: mq_send failed\n"); return; } else printf ("sendTask: mq_send succeeded\n"); } 5.14.5 Notification of Message Arrival A pthread (or task) can use the mq_notify( ) routine to request notification of the arrival of a message at an empty queue. The pthread can thereby avoid blocking or polling to wait for a message. Each queue can register only one pthread for notification at a time. Once a queue has a pthread to notify, no further attempts to register with mq_notify( ) can succeed until the notification request is satisfied or cancelled. 307 5 VxWorks Kernel Programmer's Guide, 6.6 Once a queue sends notification to a pthread, the notification request is satisfied, and the queue has no further special relationship with that particular pthread; that is, the queue sends a notification signal only once for each mq_notify( ) request. To arrange for one specific pthread to continue receiving notification signals, the best approach is to call mq_notify( ) from the same signal handler that receives the notification signals. To cancel a notification request, specify NULL instead of a notification signal. Only the currently registered pthread can cancel its notification request. The mq_notify( ) mechanism does not send notification: Example 5-10 ■ When additional messages arrive at a message queue that is not empty. That is, notification is only sent when a message arrives at an empty message queue. ■ If another pthread was blocked on the queue with mq_receive( ). ■ After a response has been made to the call to mq_notify( ). That is, only one notification is sent per mq_notify( ) call. Message Queue Notification /* * In this example, a task uses mq_notify() to discover when a message * has arrived on a previously empty queue. To run this from the shell: * * -> ld < mq_notify_test.o * -> sp exMqNotify, "greetings" * -> mq_send * */ /* includes */ #include #include #include #include #include #include #include /* defines */ #define QNAM "PxQ1" #define MSG_SIZE 64 /* limit on message sizes */ /* forward declarations */ static void exNotificationHandle (int, siginfo_t *, void *); static void exMqRead (mqd_t); 308 5 POSIX Facilities 5.14 POSIX Message Queues /**************************************************************************** * exMqNotify - example of how to use mq_notify() * * This routine illustrates the use of mq_notify() to request notification * via signal of new messages in a queue. To simplify the example, a * single task both sends and receives a message. * * RETURNS: 0 on success, or -1 * * ERRNOS: N/A */ int exMqNotify ( char * pMessage, /* text for message to self */ int loopCnt /* number of times to send a msg */ ) { struct mq_attr attr; /* queue attribute structure */ struct sigevent sigNotify; /* to attach notification */ struct sigaction mySigAction; /* to attach signal handler */ mqd_t exMqId; /* id of message queue */ int cnt = 0; /* Minor sanity check; avoid exceeding msg buffer */ if (MSG_SIZE <= strlen (pMessage)) { printf ("exMqNotify: message too long\n"); return (-1); } /* * Install signal handler for the notify signal and fill in * a sigaction structure and pass it to sigaction(). Because the handler * needs the siginfo structure as an argument, the SA_SIGINFO flag is * set in sa_flags. */ mySigAction.sa_sigaction = exNotificationHandle; mySigAction.sa_flags = SA_SIGINFO; sigemptyset (&mySigAction.sa_mask); if (sigaction (SIGUSR1, &mySigAction, NULL) == -1) { printf ("sigaction failed\n"); return (-1); } /* * Create a message queue - fill in a mq_attr structure with the * size and no. of messages required, and pass it to mq_open(). */ attr.mq_flags = 0; attr.mq_maxmsg = 2; attr.mq_msgsize = MSG_SIZE; 309 5 VxWorks Kernel Programmer's Guide, 6.6 if ((exMqId = mq_open (QNAM, O_CREAT | O_RDWR | O_NONBLOCK, 0, &attr)) == (mqd_t) - 1 ) { printf ("mq_open failed\n"); return (-1); } /* * Set up notification: fill in a sigevent structure and pass it * to mq_notify(). The queue ID is passed as an argument to the * signal handler. */ sigNotify.sigev_signo = SIGUSR1; sigNotify.sigev_notify = SIGEV_SIGNAL; sigNotify.sigev_value.sival_int = (int) exMqId; if (mq_notify (exMqId, &sigNotify) == -1) { printf ("mq_notify failed\n"); return (-1); } /* * We just created the message queue, but it may not be empty; * a higher-priority task may have placed a message there while * we were requesting notification. mq_notify() does nothing if * messages are already in the queue; therefore we try to * retrieve any messages already in the queue. */ exMqRead (exMqId); /* * Now we know the queue is empty, so we will receive a signal * the next time a message arrives. * * We send a message, which causes the notify handler to be invoked. * It is a little silly to have the task that gets the notification * be the one that puts the messages on the queue, but we do it here * to simplify the example. A real application would do other work * instead at this point. */ if (mq_send (exMqId, pMessage, 1 + strlen (pMessage), 0) == -1) { printf ("mq_send failed\n"); } /* Cleanup */ if (mq_close (exMqId) == -1) { printf ("mq_close failed\n"); return (-1); 310 5 POSIX Facilities 5.14 POSIX Message Queues } /* More cleanup */ if (mq_unlink (QNAM) == -1) { printf ("mq_unlink failed\n"); return (-1); } 5 return (0); } /**************************************************************************** * exNotificationHandle - handler to read in messages * * This routine is a signal handler; it reads in messages from a * message queue. * * RETURNS: N/A * * ERRNOS: N/A */ static void exNotificationHandle ( int sig, /* signal number */ siginfo_t * pInfo, /* signal information */ void * pSigContext /* unused (required by posix) */ ) { struct sigevent sigNotify; mqd_t exMqId; /* Get the ID of the message queue out of the siginfo structure. */ exMqId = (mqd_t) pInfo->si_value.sival_int; /* * Request notification again; it resets each time * a notification signal goes out. */ sigNotify.sigev_signo = pInfo->si_signo; sigNotify.sigev_value = pInfo->si_value; sigNotify.sigev_notify = SIGEV_SIGNAL; if (mq_notify (exMqId, &sigNotify) == -1) { printf ("mq_notify failed\n"); return; } 311 VxWorks Kernel Programmer's Guide, 6.6 /* Read in the messages */ exMqRead (exMqId); } /**************************************************************************** * exMqRead - read in messages * * This small utility routine receives and displays all messages * currently in a POSIX message queue; assumes queue has O_NONBLOCK. * * RETURNS: N/A * * ERRNOS: N/A */ static void exMqRead ( mqd_t exMqId ) { char msg[MSG_SIZE]; int prio; /* * Read in the messages - uses a loop to read in the messages * because a notification is sent ONLY when a message is sent on * an EMPTY message queue. There could be multiple msgs if, for * example, a higher-priority task was sending them. Because the * message queue was opened with the O_NONBLOCK flag, eventually * this loop exits with errno set to EAGAIN (meaning we did an * mq_receive() on an empty message queue). */ while (mq_receive (exMqId, msg, MSG_SIZE, &prio) != -1) { printf ("exMqRead: mqId (0x%x) received message: %s\n", exMqId, msg); } if (errno != EAGAIN) { printf ("mq_receive: errno = %d\n", errno); } } 312 5 POSIX Facilities 5.15 POSIX Signals 5.15 POSIX Signals VxWorks provides POSIX signal routines, as well as BSD-compatible routines and native VxWorks routines in the kernel. For information about these facilities, see 4.18 Signals, p.226. 5 5.16 POSIX Memory Management The VxWorks kernel provides POSIX memory management support for dynamic memory allocation with calloc( ), malloc( ), realloc( ), and free( ). For more information in this regard, see 6.7 Kernel Heap and Memory Partition Management, p.329. The kernel also provides the following POSIX memory locking routines: mlock( ), munlock( ), mlockall( ), and munlockall( ). However, memory mappings in VxWorks are always memory-resident. This ensures deterministic memory access for mapped files, but it also means that physical memory is continuously associated with mappings, until it is unmapped. Therefore, these POSIX memory locking routines do not do anything, and are provided simply for application portability. For information about the POSIX memory management facilities that are available only in processes, see the VxWorks Application Programmer’s Guide: POSIX Facilities. 313 VxWorks Kernel Programmer's Guide, 6.6 314 6 Memory Management Kernel Facilities 6.1 Introduction 316 6.2 Configuring VxWorks With Memory Management Facilities 317 6.3 System Memory Maps 317 6.4 Shell Commands 327 6.5 System RAM Autosizing 327 6.6 Reserved Memory 328 6.7 Kernel Heap and Memory Partition Management 329 6.8 Memory Error Detection 331 6.9 Virtual Memory Management 343 6.10 Additional Memory Protection Features 353 6.11 Processes Without MMU Support 355 315 VxWorks Kernel Programmer's Guide, 6.6 6.1 Introduction VxWorks provides memory management facilities for all code that executes in the kernel, as well as memory management facilities for applications that execute as real-time processes. This chapter deals primarily with kernel-space memory management, although it also provides information about what memory maps look like for systems that include support for processes (and related facilities). This chapter discusses the following topics: ■ The VxWorks components required for different types of memory management support. ■ The layout of memory for different configurations of VxWorks. ■ Excluding memory from VxWorks use. ■ Using run-time memory autosizing. ■ The kernel heap and memory partition management facilities that are available in the kernel. ■ Memory error detection facilities, including instrumentation provided by VxWorks components and the Wind River compiler. ■ Virtual memory management, both automated and programmatic. ■ Using the real-time process environment without an MMU. For information about the memory management facilities available to process-based applications, see VxWorks Application Programmer’s Guide: Memory Management. For information about additional error detection facilities useful for debugging software faults, see 11. Error Detection and Reporting. NOTE: This chapter provides information about facilities available in the VxWorks kernel. For information about facilities available to real-time processes, see the corresponding chapter in the VxWorks Application Programmer’s Guide. 316 6 Memory Management 6.2 Configuring VxWorks With Memory Management Facilities 6.2 Configuring VxWorks With Memory Management Facilities Information about configuring VxWorks with various memory management facilities is provided in the context of the discussions of those facilities. See: ■ ■ ■ ■ ■ ■ ■ 6.4 Shell Commands, p.327 6.5 System RAM Autosizing, p.327 6.6 Reserved Memory, p.328 6.7 Kernel Heap and Memory Partition Management, p.329 6.8 Memory Error Detection, p.331 6.9 Virtual Memory Management, p.343 6.11 Processes Without MMU Support, p.355 6 6.3 System Memory Maps This section describes the VxWorks memory map as it appears with different configurations and run-time activity: ■ A system without process support. ■ A system with process support, but without processes running. ■ A system with process support and two processes running, as well as a shared library and a shared data region. In addition, it describes various memory views within a single system. 317 VxWorks Kernel Programmer's Guide, 6.6 6.3.1 System Memory Map Without Process Support In a VxWorks system RAM is delimited by: ■ The LOCAL_MEM_LOCAL_ADRS BSP configuration parameter, which defines the start of the system RAM. ■ The address returned by the routine sysPhysMemTop( ), which is at the top of system RAM. This address is either determined at run-time if RAM autosizing is enabled (see 6.5 System RAM Autosizing, p.327). If autosizing is disabled, then sysPhysMemTop( ) is calculated using the BSP configuration parameter LOCAL_MEM_SIZE; that is sysPhysMemTop( ) returns LOCAL_MEM_LOCAL_ADRS + LOCAL_MEM_SIZE. (LOCAL_MEM_LOCAL_ADRS and LOCAL_MEM_SIZE are configuration parameters of the INCLUDE_MEMORY_CONFIG component.) System RAM must be contiguous. For systems without an MMU or with the MMU disabled, this means that the system RAM must be in contiguous physical memory. For systems with and MMU enabled, the system RAM must be mapped contiguously in virtual memory. In the latter case, the physical space may be non-contiguous for some architectures that do not require an identity mapped kernel. For the architecture specific requirements, see the VxWorks Architecture Supplement. ! CAUTION: The SMP configuration of VxWorks does not support MMU-less configurations. For information about VxWorks SMP, see 15. VxWorks SMP. Within system RAM, the elements of a VxWorks system are arranged as follows: ■ Below RAM_LOW_ADRS there is an architecture specific layout of memory blocks used for saving boot parameters, the system exception message area, the exception or interrupt vector table, and so on. For specific details, see the VxWorks Architecture Supplement. ■ The kernel code (text, data, and bss) starting at address RAM_LOW_ADRS. ROM-resident images are an exception, for which the text segment is located outside of the system RAM (see 2.4.1 VxWorks Image Types, p.15). ■ The WDB target agent memory pool is located immediately above the kernel code, if WDB is configured into the system (see 12.6 WDB Target Agent, p.626). ■ The kernel heap follows the WDB memory pool. ■ An optional area of persistent memory. 318 6 Memory Management 6.3 System Memory Maps ■ An optional area of user-reserved memory may be located above the kernel heap. Figure 6-1 illustrates a typical memory map for a system without process support. For a comparable illustration of a system with process support—which means it has unmapped memory available for processes that have not yet been created—see Figure 6-2. Note that the memory pool for the WDB target agent is present only if WDB is configured into the kernel. Without WDB, the kernel heap starts right above the end of the kernel BSS ELF segment. The routine sysMemTop( ) returns the end of the kernel heap area. If both the user-reserved memory size (USER_RESERVED_MEM) and the persistent memory size (PM_RESERVED_MEM) are zero, then sysMemTop( ) returns the same value than sysPhysMemTop( ), and the kernel heap extends to the end of the system RAM area. For more information about configuring user-reserved memory and persistent memory. See 6.6 Reserved Memory, p.328 for more information. Also see 6.3.2 System Memory Map with Process Support, p.321. 319 6 VxWorks Kernel Programmer's Guide, 6.6 Figure 6-1 Fig 5-1: Memory Map of a System Without Process Support LOCAL_MEM_LOCAL_ADRS (start of system RAM) RAM_LOW_ADRS (start of kernel text) Kernel Image (text + rodata + data + bss) WDB Memory Pool End of Kernel BSS (optional) Start of Kernel Heap Kernel Heap (System Memory Partition) User-Reserved Memory Area (optional) ED&R Persistent Memory Area sysMemTop( ) = sysPhysMemTop( ) USR_RESERVED_MEM PM_RESERVED_MEM sysPhysMemTop( ) - PM_RESERVED_MEM (optional) sysPhysMemTop( ) (end of system RAM) 320 6 Memory Management 6.3 System Memory Maps 6.3.2 System Memory Map with Process Support Kernel applications have access to the same memory management facilities as described in 6.3 System Memory Maps, p.317, whether process support is included or not. The only difference between the two configurations relates to the size of the kernel heap. Without process support, the kernel heap extends up to sysMemTop( ). With process support the kernel heap does not extend up to sysMemTop( ), but instead uses the KERNEL_HEAP_SIZE parameter (set in the INCLUDE_RTP component) as its size. This parameter is disregarded if process support is not included in VxWorks. By default, KERNEL_HEAP_SIZE is set to two-thirds of the RAM located between sysMemTop( ) and the end of the kernel code, or the end of the WDB memory pool when the WDB component is included into the system configuration. Figure 6-2 illustrates this configuration. The RAM located between sysMemTop( ) and the end of the kernel heap is left unmapped. RAM pages are allocated from that unmapped RAM area when process, shared library, or shared data region space must be mapped. For a comparable image of a system without process support, see Figure 6-1. 321 6 VxWorks Kernel Programmer's Guide, 6.6 Figure 6-2 Fig 5-2: Memory Map of a System With Process Support LOCAL_MEM_LOCAL_ADRS RAM_LOW_ADRS Kernel Image (text + rodata + data + bss) WDB Memory Pool End of Kernel BSS (optional) Kernel Heap Start of Kernel Heap KERNEL_HEAP_SIZE End of Kernel Heap RAM initially unmapped (dynamically mapped when creating RTPs, SLs, or SDs) User-Reserved Memory Area (optional) ED&R Persistent Memory Area sysMemTop( ) = sysPhysMemTop( ) USR_RESERVED_MEM PM_RESERVED_MEM sysPhysMemTop( ) - PM_RESERVED_MEM (optional) sysPhysMemTop( ) 322 6 Memory Management 6.3 System Memory Maps The default setting of KERNEL_HEAP_SIZE should be adjusted to meet the requirements of the system. 6.3.3 System Memory Map with Processes Running A VxWorks system configured for real-time processes may have one or more applications executing as processes at run-time. It may also have shared libraries and shared data regions instantiated. The kernel, each of the processes, shared libraries, and shared data regions occupy a discrete space in virtual memory. Each VxWorks process has its own region of virtual memory; processes do not overlap in virtual memory. This flat virtual-memory map provides advantages in speed, in a programming model that accommodates systems with and without an MMU, and in debugging applications (see 6.11 Processes Without MMU Support, p.355). The virtual space assigned to a process is not necessarily composed of one large contiguous block of virtual memory. In some cases it will be composed of several smaller blocks of virtual space which are discontinuous from each other. Figure 6-3 illustrates the memory map of a system with the kernel areas (RAM and I/O), two different processes (RTP A and RTP B), as well as one shared library, and one shared data region. 323 6 VxWorks Kernel Programmer's Guide, 6.6 Figure 6-3 Fig 5-3: Memory Map of a System With Two Processes Kernel Code + Kernel Heap + Kernel Task Stacks + Kernel Object Modules RTP A Code RTP B Heap Kernel Memory Space RTP B Task Stacks RTP A Memory Space RTP A Heap RTP B Memory Space Shared Library Shared Library and Shared Data Memory Space RTP B Code RTP A Tasks Stacks Shared Data Region I/O Region 1 I/O Region 2 324 6 Memory Management 6.3 System Memory Maps Each process has its own virtual memory context, defined by its MMU translation table used to map virtual and physical memory, and other information about each page of memory. This memory context describes the virtual space that all of the tasks in a the process can access. In other words, it defines the memory view of a process. The kernel space is mapped with supervisor access privilege in the memory context of each process (but not with user mode privilege). Therefore tasks executing in a process can access kernel memory space only in system calls, during which the execution is switched to supervisor mode. (For information about system calls, see VxWorks Application Programmer’s Guide: Applications and Processes.) A shared library or shared data region is mapped into the virtual context of a process only when the process’ application code opens or creates it, and it effectively disappears from the process’ memory view when the application closes or deletes the shared library or shared data region. Figure 6-4 illustrates the different memory views of a system with two processes (RTP A and RTP B), a shared library that both RTP A and RTP B opened, as well as a shared data region that both a kernel application and RTP B opened. The first memory view corresponds to the memory space accessible by kernel tasks. The second and third memory views correspond to the memory space accessible by tasks executing in process A, respectively process B. Note that the grayed areas are only accessible during system calls. 325 6 VxWorks Kernel Programmer's Guide, 6.6 Figure 6-4 Fig 5-4: System Memory Views Kernel Memory View Kernel Code + Kernel Heap + Kernel Task Stacks + Kernel Object Modules RTP A Memory View Kernel Code + Kernel Heap + Kernel Task Stacks + Kernel Object Modules RTP B Memory View Kernel Code + Kernel Heap + Kernel Task Stacks + Kernel Object Modules RTP A Code RTP B Heap RTP B Task Stacks RTP A Heap Shared Library Shared Library RTP B Code RTP A Tasks Stacks Shared Data Region 326 Shared Data Region I/O Region 1 I/O Region 1 I/O Region 1 I/O Region 2 I/O Region 2 I/O Region 2 6 Memory Management 6.4 Shell Commands Note that on system without an MMU, or with the MMU disabled, there is only one memory view shared by the kernel and all process tasks. This memory view corresponds to Figure 6-3. Any task in the system, whether it is a kernel or a task executing in a process, has access to all the memory: kernel space, I/O regions, any processes memory, shared libraries, and shared data regions. In other words, such configurations do not provide any memory protection. For more information, see 6.11 Processes Without MMU Support, p.355. 6 6.4 Shell Commands The shell’s adrSpaceShow( ) show routine (for the C interpreter) or the adrsp info command (for the command interpreter) can be used to display an overview of the address space usage at time of the call. These are included in the kernel with the INCLUDE_ADR_SPACE_SHOW and INCLUDE_ADR_SPACE_SHELL_CMD components, respectively. The rtpMemShow( ) show routine or the rtp meminfo command can be used to display the private mappings of a process. These are included with the INCLUDE_RTP_SHOW and INCLUDE_RTP_SHOW_SHELL_CMD components, respectively. The kernel mappings can be displayed with the vmContextShow( ) show routine or the vm context command. These are included with the INCLUDE_VM_SHOW and INCLUDE_VM_SHOW_SHELL_CMD components, respectively. 6.5 System RAM Autosizing When RAM autosizing is supported by the BSP, defining the configuration parameter LOCAL_MEM_AUTOSIZE will enable run time memory sizing. The default definition state for this parameter and the implementation itself is BSP-dependent. Check the BSP reference to see if this feature is supported or not. When autosizing is supported by the BSP and LOCAL_MEM_AUTOSIZE is defined, the top of system RAM as reported by sysPhysMemTop( ) is the value determined at run-time. 327 VxWorks Kernel Programmer's Guide, 6.6 If the LOCAL_MEM_AUTOSIZE is not defined, the top of the system RAM as reported by sysPhysMemTop( ) is the address calculated as: (LOCAL_MEM_LOCAL_ADRS + LOCAL_MEM_SIZE) If the BSP is unable to perform run time memory sizing then a compile time error should be generated, informing the user of the limitation. LOCAL_MEM_AUTOSIZE, LOCAL_MEM_LOCAL_ADRS and LOCAL_MEM_SIZE are parameters of the INCLUDE_MEM_CONFIG component. 6.6 Reserved Memory Two types of reserved memory can be configured in VxWorks system RAM: user-reserved memory and persistent memory. Reserved memory is not cleared by VxWorks at startup or during system operation. Boot loaders may or may not clear the area; see Boot Loaders and Reserved Memory, p.328. User-reserved memory, configured with the BSP parameter USER_RESERVED_MEM, is part of the system RAM that can managed by kernel applications independently of the kernel heap. Persistent memory, configured with the parameter PM_RESERVED_MEM, is the part of system RAM that is used by the error detection and reporting facilities (see 11. Error Detection and Reporting). For the layout of the user-reserved memory and the persistent memory, see figures Figure 6-1 and Figure 6-2. Boot Loaders and Reserved Memory Boot loaders may or may not clear reserved memory, depending on the configuration that was used to create them. If the boot loader is built with both USER_RESERVED_MEM and PM_RESERVED_MEM set to zero, the system RAM is cleared through the address calculated as: (LOCAL_MEM_LOCAL_ADRS + LOCAL_MEM_SIZE) To ensure that reserved memory is not cleared, the boot loader should be created with the USER_RESERVED_MEM and the PM_RESERVED_MEM parameter set to the desired sizes; that is, the same values that are used to build the downloaded VxWorks image. 328 6 Memory Management 6.7 Kernel Heap and Memory Partition Management For information about VxWorks boot loaders, see 3. Boot Loader. NOTE: If autosizing of system RAM is enabled, the top of the system RAM detected at run-time may be different from the address calculated as LOCAL_MEM_LOCAL_ADRS + LOCAL_MEM_SIZE, resulting in non-identical location of the memory range not being cleared by the boot loader. For more information about autosizing, see 6.5 System RAM Autosizing, p.327. 6 6.7 Kernel Heap and Memory Partition Management VxWorks provides facilities for heap access and memory partition management. The memLib and memPartLib libraries provide routines to access the kernel heap, including standard ANSI-compatible routines as well as routines to manipulate kernel memory partitions. The kernel heap is used by all code running in the kernel, including kernel libraries and components, kernel applications, and by processes when executing system calls. Memory partitions consist of areas of memory that are used for dynamic memory allocations by applications and kernel components. Memory partitions may be used to reserve portions of memory for specific applications, or to isolate dynamic memory usage on an application basis. The kernel heap is a specific memory partition, which is also referred to as the system memory partition. 6.7.1 Configuring the Kernel Heap and the Memory Partition Manager There are two kernel components for configuring the kernel heap and the memory partition manager. The core functionality for both the kernel heap and memory partition is provided by the INCLUDE_MEM_MGR_BASIC component (see the VxWorks API reference for memPartLib). The INCLUDE_MEM_MGR_FULL component extends the functionality required for a full-featured heap and memory partition manager (see the VxWorks API reference for memLib). The kernel heap is automatically created by the system when either one of these components are included in the VxWorks configuration. The size of the kernel heap is set as described in 6.3 System Memory Maps, p.317; see Figure 6-1 and Figure 6-2. 329 VxWorks Kernel Programmer's Guide, 6.6 Information about allocation statistics in the kernel heap and in kernel memory partitions can be obtained with the show routines provided with the INCLUDE_MEM_SHOW component. For more information, see the VxWorks API reference for memShow. 6.7.2 Basic Heap and Memory Partition Manager The memPartLib library (INCLUDE_MEM_MGR_BASIC) provides the core facilities for memory partition support, including some of the standard ANSI-compatible routines such as malloc( ), and free( ). The core functionality of memPartLib provides for the following API: ■ Creation and deletion of memory partitions with memPartCreate( ) and memPartDelete( ). ■ Addition of memory to a specific memory partition with memPartAddToPool( ), or to the heap with memAddToPool( ). ■ Allocation and freeing of memory blocks from a specific memory partitions with memPartAlloc( ), memPartAlignedAlloc( ), and memPartFree( ); and from the heap with malloc( ) and free( ). 6.7.3 Full Heap and Memory Partition Manager The memLib library (provided by the INCLUDE_MEM_MGR_FULL component) adds a few more routines to provide a full-featured memory partition and heap allocator. The features provided in this library are: ■ Allocation of memory aligned to a specific boundary with memalign( ), and alignment to a page with valloc( ). ■ Reallocation of blocks of memory in a specific partition with memPartRealloc( ), or in the heap with realloc( ). ■ The ANSI-compatible routines calloc( ), and cfree( ). ■ Obtaining memory partition statistics with routines memPartInfoGet( ) and memPartFindMax( ), or in the heap with memFindMax( ) and memInfoGet( ). ■ Built-in error checking. This feature is controlled with the heap and partition options. Two types of errors can be enabled. The first type, block error, is detected during block validation in free( ), realloc( ), memPartFree( ) and memPartRealloc( ). The second type, allocation error, is detected by any of the 330 6 Memory Management 6.8 Memory Error Detection allocation and re-allocation routines. There are options to enable logging an error message and/or to suspend the task hitting the error. Setting and getting error handling options of a specific memory partition can be done with memPartOptionsSet( ) and memPartOptionsGet( ). The debugging options for the heap are controlled with memOptionsSet( ) and memOptionGet( ). Additional heap and memory partition error detection is provided with heap and partition memory instrumentation (see 6.8.1 Heap and Partition Memory Instrumentation, p.331). For more information, see the VxWorks API references for memPartLib and memLib. 6.8 Memory Error Detection Support for memory error detection is provided by two optional instrumentation libraries. The memEdrLib library performs error checks of operations in the kernel heap and memory partitions in the kernel. The Run-Time Error Checking (RTEC) feature of the Wind River Compiler can be used to check for additional errors, such as buffer overruns and underruns, static and automatic variable reference checks. Errors detected by these facilities are reported by the error detection and reporting facility, which must, therefore be included in the VxWorks kernel configuration. See 11. Error Detection and Reporting. 6.8.1 Heap and Partition Memory Instrumentation To supplement the error detection features built into memLib and memPartLib (such as valid block checking), components can be added to VxWorks to perform automatic, programmatic, and interactive error checks on memLib and memPartLib operations. The components help detect common programming errors such as double-freeing an allocated block, freeing or reallocating an invalid pointer, memory leaks. In addition, with compiler-assisted code instrumentation, they help detect bounds-check violations, buffer over-runs and under-runs, pointer references to free memory blocks, pointer references to automatic variables outside the scope of the variable, and so on. Note that compiler-assisted instrumentation must be used 331 6 VxWorks Kernel Programmer's Guide, 6.6 in order to track buffer underruns and overruns. For information about compiler instrumentation, see 6.8.2 Compiler Instrumentation, p.338. Errors detected by the automatic checks are logged by the error detection and reporting facility. Configuring VxWorks with Memory Partition and Heap Instrumentation To enable the basic level of memory partition and heap instrumentation, the following components must be included into the kernel configuration: ■ INCLUDE_MEM_EDR, includes the basic memory partition debugging functionality and instrumentation code. ■ INCLUDE_EDR_ERRLOG, INCLUDE_EDR_POLICIES and INCLUDE_EDR_SHOW for error detection, reporting, and persistent memory. For more information see 11. Error Detection and Reporting. The following component may also be included: ■ INCLUDE_MEM_EDR_SHOW, for enabling the show routines. In addition, the following parameters of the INCLUDE_MEM_EDR component can be modified: MEDR_EXTENDED_ENABLE Set to TRUE to enable logging trace information for each allocated block, but at the cost of increased memory used to store entries in the allocation database. The default setting is FALSE. MEDR_FILL_FREE_ENABLE Set to TRUE to enable pattern-filling queued free blocks. This aids detecting writes into freed buffers. The default setting is FALSE. MEDR_FREE_QUEUE_LEN Maximum length of the free queue. When a memory block is freed, instead of immediately returning it to the partition's memory pool, it is kept in a queue. This is useful for detecting references to a memory block after it has been freed. When the queue reaches the maximum length allowed, the blocks are returned to the respective memory pool in a FIFO order. Queuing is disabled when this parameter is 0. Default setting for this parameter is 64. MEDR_BLOCK_GUARD_ENABLE Enable guard signatures in the front and the end of each allocated block. Enabling this feature aids in detecting buffer overruns, underruns, and some heap memory corruption. The default setting is FALSE. 332 6 Memory Management 6.8 Memory Error Detection MEDR_POOL_SIZE Set the size of the memory pool used to maintain the memory block database. Default setting in the kernel is 1MB. The database uses 32 bytes per memory block without extended information enabled, and 64 bytes per block with extended information enabled (call stack trace). This pool is allocated from the kernel heap. Error Types During execution, errors are automatically logged when the allocation, free, and re-allocation functions are called. The following error types are automatically identified and logged: ■ Allocation returns block address within an already allocated block from the same partition. This would indicate corruption in the partition data structures. ■ Allocation returns block address that is in the task's stack space. This would indicate corruption in the partition data structures. ■ Allocation returns block address that is in the kernel's static data section. This would indicate corruption in the partition data structures. ■ Freeing a pointer that is in the task’s stack space. ■ Freeing memory that was already freed and is still in the free queue. ■ Freeing memory that is in the kernel’s static data section. ■ Freeing memory in a different partition than the one in which it was allocated. ■ Freeing a partial memory block. ■ Freeing a memory block with the guard zone corrupted, when the MEDR_BLOCK_GUARD_ENABLE environment variable is TRUE. ■ Pattern in a memory block which is in the free queue has been corrupted, when the MEDR_FILL_FREE_ENABLE environment variable is TRUE. Shell Commands The show routines and commands described in Table 6-1 are available for use with the shell’s C and command interpreters to display information. 333 6 VxWorks Kernel Programmer's Guide, 6.6 Table 6-1 Shell Commands C Interpreter Command Interpreter Description edrShow( ) edr show Displays error records. memEdrPartShow( ) mem part list Displays a summary of the instrumentation information for memory partitions in the kernel. memEdrBlockShow( ) mem block list Displays information about allocated blocks. Blocks can be selected using a combination of various querying criteria: partition ID, block address, allocating task ID, block type. memEdrFreeQueueFlush( ) mem queue flush Flushes the free queue. When this routine is called, freeing of all blocks in the free queue is finalized so that all corresponding memory blocks are returned the free pool of the respective partition. memEdrBlockMark( ) Marks or unmarks selected blocks allocated at the time of the call. The selection criteria may include partition ID and/or allocating task ID. This routine can be used to monitor memory leaks by displaying information of unmarked blocks with memBlockShow( ) or mem block list. 334 mem block mark and mem block unmark 6 Memory Management 6.8 Memory Error Detection Code Example The following kernel application code is used to demonstrate various errors detected with the heap and partition memory instrumentation (line numbers are included for reference purposes). Its use is illustrated in Shell Session Example, p.335. #include #include 6 void heapErrors (void) { char * pChar; pChar = malloc (24); free (pChar + 2); free (pChar); free (pChar); pChar = malloc (32); } /* free partial block */ /* double-free block */ /* leaked memory */ Shell Session Example The following shell session is executed with the C interpreter. The sample code listed above is compiled and linked in the VxWorks kernel (see 2.6.8 Linking Kernel Application Object Modules with VxWorks, p.64). The kernel must include the INCLUDE_MEM_EDR and INCLUDE_MEM_EDR_SHOW components. In order to enable saving call stack information, the parameter MEDR_EXTENDED_ENABLE is set TRUE. Also, the kernel should be configured with the error detection and reporting facility, including the show routines, as described in 11.2 Configuring Error Detection and Reporting Facilities, p.564. First mark all allocated blocks: -> memEdrBlockMark value = 6390 = 0x18f6 Next, clear the error log. This step is optional, and is done only to start with a clean log: -> edrClear value = 0 = 0x0 The kernel application may be started in a new task spawned with the sp( ) utility, as follows: -> taskId = sp (heapErrors) New symbol "taskId" added to kernel symbol table. Task spawned: id = 0x246d010, name = t1 taskId = 0x2469ed0: value = 38195216 = 0x246d010 335 VxWorks Kernel Programmer's Guide, 6.6 At this point the application finished execution. The following command lists the memory blocks allocated, but not freed by the application task. Note that the listing shows the call stack at the time of the allocation: -> memEdrBlockShow 0, 0, taskId, 5, 1 Addr Type Size Part ID Task ID Task Name Trace -------- ------ -------- -------- -------- ------------ -----------246d7a0 alloc 32 269888 246d010 -t1 heapErrors() memPartAlloc() 0x001bdc88() Errors detected while executing the application are logged in persistent memory region. 336 6 Memory Management 6.8 Memory Error Detection Display the log using edrShow( ). The first error corresponds to line 9 in the test code; the second error corresponds to line 12. -> edrShow ERROR LOG ========= Log Size: Record Size: Max Records: CPU Type: Errors Missed: Error count: Boot count: Generation count: 524288 bytes (128 pages) 4096 bytes 123 0x5a 0 (old) + 0 (recent) 2 20 94 6 ==[1/2]============================================================== Severity/Facility: NON-FATAL/KERNEL Boot Cycle: 20 OS Version: 6.0.0 Time: THU JAN 01 00:00:31 1970 (ticks = 1880) Task: "t1" (0x0246d010) freeing part of allocated memory block PARTITION: 0x269888 PTR=0x246bea2 BLOCK: allocated at 0x0246bea0, 24 bytes <<<< >>>> 0x0011d240 0x00111364 0x001c26f8 0x001bdc6c vxTaskEntry +0x54 : heapErrors +0x24 : memPartFree +0xa4 : memEdrItemGet+0x588: heapErrors () free () 0x001bdbb4 () 0x001bd71c () ==[2/2]============================================================== Severity/Facility: NON-FATAL/KERNEL Boot Cycle: 20 OS Version: 6.0.0 Time: THU JAN 01 00:00:31 1970 (ticks = 1880) Task: "t1" (0x0246d010) freeing memory in free list PARTITION: 0x269888 PTR=0x246bea0 BLOCK: free block at 0x0246bea0, 24 bytes <<<< >>>> 0x0011d240 vxTaskEntry +0x54 : 0x00111374 heapErrors +0x34 : 0x001c26f8 memPartFree +0xa4 : 0x001bdc6c memEdrItemGet+0x588: value = 0 = 0x0 heapErrors () free () 0x001bdbb4 () 0x001bd71c () 337 VxWorks Kernel Programmer's Guide, 6.6 6.8.2 Compiler Instrumentation Additional errors are detected if the application is compiled using the Run-Time Error Checking (RTEC) feature of the Wind River Compiler (Diab). The following flag should be used: -Xrtc=option NOTE: This feature is not available with the GNU compiler. Code compiled with the -Xrtc flag is instrumented for run-time checks such as pointer reference check and pointer arithmetic validation, standard library parameter validation, and so on. These instrumentations are supported through the memory partition run-time error detection library. Table 6-2 lists the -Xrtc options that are supported. Note that using the -Xrtc flag without specifying any options is the same as using them all. Table 6-2 -Xrtc Options Option Description 0x01 register and check static (global) variables 0x02 register and check automatic variables 0x08 pointer reference checks 0x10 pointer arithmetic checks 0x20 pointer increment/decrement checks 0x40 standard function checks; for example memset( ) and bcopy( ) 0x80 report source code filename and line number in error logs 338 6 Memory Management 6.8 Memory Error Detection The errors and warnings detected by the RTEC compile-in instrumentation are logged by the error detection and reporting facility (see 11. Error Detection and Reporting). The following error types are identified: ■ ■ ■ ■ ■ ■ Bounds-check violation for allocated memory blocks. Bounds-check violation of static (global) variables. Bounds-check violation of automatic variables. Reference to a block in the free queue. Reference to the free part of the task’s stack. De-referencing a NULL pointer. 6 Configuring VxWorks for RTEC Support Support for this feature in the kernel is enabled by adding the INCLUDE_MEM_EDR_RTC component, as well as the components described in section Configuring VxWorks with Memory Partition and Heap Instrumentation, p.332. Shell Commands The compiler provided instrumentation automatically logs errors detected in applications using the error detection and reporting facility. For a list of the shell commands available for error logs see 11.4 Displaying and Clearing Error Records, p.568. Code Example Application code built with the RTEC instrumentation has compiler-generated constructors. To ensure that the constructors are called when a module is dynamically downloaded, the module must be processed similarly to a C++ application. For example, the following make rule can be used: TGT_DIR=$(WIND_BASE)/target %.out : %.c @ $(RM) $@ $(CC) $(CFLAGS) -Xrtc=0xfb $(OPTION_OBJECT_ONLY) $< @ $(RM) ctdt_$(BUILD_EXT).c $(NM) $(basename $@).o | $(MUNCH) > ctdt_$(BUILD_EXT).c $(MAKE) CC_COMPILER=$(OPTION_DOLLAR_SYMBOLS) ctdt_$(BUILD_EXT).o $(LD_PARTIAL) $(LD_PARTIAL_LAST_FLAGS) $(OPTION_OBJECT_NAME)$@ $(basename $@).o ctdt_$(BUILD_EXT).o include $(TGT_DIR)/h/make/rules.library 339 VxWorks Kernel Programmer's Guide, 6.6 The the following application code generates various errors that can be recorded and displayed (line numbers are included for reference purposes). Its use is illustrated in Shell Session Example, p.340. #include #include #include void refErrors () { char name[] = "very_long_name"; char * pChar; int state[] = { 0, 1, 2, 3 }; int ix = 0; pChar = malloc (13); memcpy (pChar, name, strlen (name)); /* bounds check violation */ /* of allocated block */ for (ix = 0; ix < 4; ix++) state[ix] = state [ix + 1]; /* bounds check violation */ free (pChar); memcpy (pChar, "another_name", 12); } /* reference a free block */ Shell Session Example The following shell session log is executed with the C interpreter. The sample code listed above is compiled and linked in the VxWorks kernel (see 2.6.8 Linking Kernel Application Object Modules with VxWorks, p.64). The kernel must include the INCLUDE_MEM_EDR and INCLUDE_MEM_EDR_RTC components. Also, the kernel should be configured with the error detection and reporting facility, including the show routines, as described in 11.2 Configuring Error Detection and Reporting Facilities, p.564. First, clear the error log to start with a clean log: -> edrClear value = 0 = 0x0 Start the kernel application in a new task spawned with the sp( ) utility: -> sp refErrors Task spawned: id = 0x246d7d0, name = t2 value = 38197200 = 0x246d7d0 At this point the application finished execution. Errors detected while executing the application are logged in the persistent memory region. Display the log using 340 6 Memory Management 6.8 Memory Error Detection edrShow( ). In the example below, the log display is interspersed with description of the errors. -> edrShow ERROR LOG ========= Log Size: Record Size: Max Records: CPU Type: Errors Missed: Error count: Boot count: Generation count: 524288 bytes (128 pages) 4096 bytes 123 0x5a 0 (old) + 0 (recent) 3 21 97 6 The first error corresponds to line 13 in the test code. A string of length 14 is copied into a allocated buffer of size 13: ==[1/3]============================================================== Severity/Facility: NON-FATAL/KERNEL Boot Cycle: 21 OS Version: 6.0.0 Time: THU JAN 01 00:14:22 1970 (ticks = 51738) Task: "t2" (0x0246d7d0) Injection Point: refErr.c:13 memory block bounds-check violation PTR=0x246be60 OFFSET=0 SIZE=14 BLOCK: allocated at 0x0246be60, 13 bytes <<<< >>>> 0x0011d240 vxTaskEntry +0x54 : 0x00111390 () 0x00111470 refErrors +0xe4 : __rtc_chk_at () 0x001bd02c memEdrErrorLog+0x13c: _sigCtxSave () 341 VxWorks Kernel Programmer's Guide, 6.6 The second error refers to line 18: the local state array is referenced with index 4. Since the array has only four elements, the range of valid indexes is 0 to 3: ==[2/3]============================================================== Severity/Facility: NON-FATAL/KERNEL Boot Cycle: 21 OS Version: 6.0.0 Time: THU JAN 01 00:14:22 1970 (ticks = 51738) Task: "t2" (0x0246d7d0) Injection Point: refErr.c:18 memory block bounds-check violation PTR=0x278ba94 OFFSET=16 SIZE=4 BLOCK: automatic at 0x0278ba94, 16 bytes <<<< >>>> 0x0011d240 vxTaskEntry +0x54 : 0x00111390 () 0x001114a0 refErrors +0x114: __rtc_chk_at () 0x001bd02c memEdrErrorLog+0x13c: _sigCtxSave () The last error is caused by the code on line 22. A memory block that has been freed is being modified: ==[3/3]============================================================== Severity/Facility: NON-FATAL/KERNEL Boot Cycle: 21 OS Version: 6.0.0 Time: THU JAN 01 00:14:22 1970 (ticks = 51739) Task: "t2" (0x0246d7d0) Injection Point: refErr.c:22 pointer to free memory block PTR=0x246be60 OFFSET=0 SIZE=12 BLOCK: free block at 0x0246be60, 13 bytes <<<< >>>> 0x0011d240 vxTaskEntry +0x54 : 0x00111390 () 0x00111518 refErrors +0x18c: __rtc_chk_at () 0x001bd02c memEdrErrorLog+0x13c: _sigCtxSave () 342 6 Memory Management 6.9 Virtual Memory Management 6.9 Virtual Memory Management VxWorks can be configured with an architecture-independent interface to the CPU’s memory management unit (MMU) to provide virtual memory support. This support includes the following features: ■ Setting up the kernel memory context at boot time. ■ Mapping pages in virtual space to physical memory. ■ Setting caching attributes on a per-page basis. ■ Setting protection attributes on a per-page basis. ■ Setting a page mapping as valid or invalid. ■ Locking and unlocking TLB entries for pages of memory. ■ Enabling page optimization. 6 The programmable elements of virtual memory (VM) support are provided by the vmBaseLib library. NOTE: There are differences in the vmBaseLib library provided for the symmetric multiprocessor (SMP) and uniprocessor (UP) configurations of VxWorks, and special guidelines for its use in optimizing SMP applications. For more information about vmBaseLib and SMP, see vmBaseLib Restrictions, p.709 and Using vmBaseLib, p.701. For general information about VxWorks SMP and about migration, see 15. VxWorks SMP and 15.15 Migrating Code to VxWorks SMP, p.702. When process (RTP) support is included in VxWorks with the INCLUDE_RTP component, the virtual memory facilities also provide system support for managing multiple virtual memory contexts, such as creation and deletion of process memory context. For information about additional MMU-based memory protection features beyond basic virtual memory support, see 6.10 Additional Memory Protection Features, p.353. Also note that errors (exceptions) generated with the use of virtual memory features can be detected and managed with additional VxWorks facilities. See 11. Error Detection and Reporting for more information. 343 VxWorks Kernel Programmer's Guide, 6.6 6.9.1 Configuring Virtual Memory Management The components listed in Table 6-3 provide basic virtual memory management, as well as show routines for use from the shell. Table 6-3 MMU Components Constant Description INCLUDE_MMU_GLOBAL_MAP Initialize the kernel's global MMU mappings according to the BSP's sysPhysMemDesc[ ] table. See Configuring the Kernel Virtual Memory Context, p.344. INCLUDE_MMU_BASIC Include the vmBaseLib API, which is used for programmatic management of virtual memory (see 6.9.2 Managing Virtual Memory Programmatically, p.346). INCLUDE_LOCK_TEXT_SECTION Kernel text TLB locking optimization. INCLUDE_PAGE_SIZE_OPTIMIZATION Page size optimization for the kernel. INCLUDE_VM_SHOW Virtual memory show routines for the shell C interpreter. INCLUDE_VM_SHOW_SHELL_CMD Virtual memory show commands for the shell command interpreter. For information about related components see 6.10 Additional Memory Protection Features, p.353. Configuring the Kernel Virtual Memory Context The kernel virtual memory context is created automatically at boot time based on configuration data provided by the BSP. The primary data is in the sysPhysMemDesc[ ] table, which is usually defined in the BSP’s sysLib.c file. The table defines the initial kernel mappings and initial attributes. The entries in this table are of PHYS_MEM_DESC structure type, which is defined in vmLib.h. There is usually no need to change the default sysPhysMemDesc[ ] configuration. However, modification may be required or advisable, for example, when: 344 6 Memory Management 6.9 Virtual Memory Management ■ New driver support or new devices (for example, flash memory) are added to the system. ■ The protection or cache attributes of certain entries must be changed. For example, entries for flash memory can be read-only if the content of the flash is never written from VxWorks. However, if a flash driver such as TrueFFS is used, the protection attribute has to be set to writable. ■ There are unused entries in the table. In general, it is best to keep only those entries that actually describe the system, as each entry may require additional system RAM for page tables (depending on size of the entry, its location relative to other entries, and architecture-specific MMU parameters). The larger the memory blocks mapped, the more memory is used for page tables. The sysPhysMemDesc[ ] table can be modified at run-time. This is useful, for example, with PCI drivers that can be auto-configured, which means that memory requirements are detected at run-time. In this case the size and address fields can be updated programmatically for the corresponding sysPhysMemDesc[ ] entries. It is important to make such updates before the VM subsystem is initialized by usrMmuInit( ), for example during execution of sysHwInit( ). ! CAUTION: The regions of memory defined in sysPhysMemDesc[ ] must be page-aligned, and must span complete pages. In other words, the first three fields (virtual address, physical address, and length) of a PHYS_MEM_DESC structure must all be even multiples of the MMU page size. Specifying elements of sysPhysMemDesc[ ] that are not page-aligned causes the target to reboot during initialization. See the VxWorks Architecture Supplement to determine what page size is supported for the architecture in question. Configuration Example This example is based on multiple CPUs using the shared-memory network. A separate memory board is used for the shared-memory pool. Because this memory is not mapped by default, it must be added to sysPhysMemDesc[ ] for all the boards on the network. The memory starts at 0x4000000 and must be made non-cacheable, as shown in the following code fragment: 345 6 VxWorks Kernel Programmer's Guide, 6.6 /* shared memory */ { (VIRT_ADDR) 0x4000000, /* virtual address */ (PHYS_ADDR) 0x4000000, /* physical address */ 0x20000, /* length */ /* initial state mask */ MMU_ATTR_VALID_MSK | MMU_ATTR_PROT_MSK | MMU_ATTR_CACHE_MSK, /* initial state */ MMU_ATTR_VALID | MMU_ATTR_PROT_SUP_READ | MMU_ATTR_PROT_SUP_WRITE | MMU_ATTR_CACHE_OFF } For some architectures, the system RAM (the memory used for the VxWorks kernel image, kernel heap, and so on) must be identity mapped. This means that for the corresponding entry in the sysPhysMemDesc[ ] table, the virtual address must be the same as the physical address. For more information see 6.3 System Memory Maps, p.317 and the VxWorks Architecture Supplement. 6.9.2 Managing Virtual Memory Programmatically This section describes the facilities provided for manipulating the MMU programmatically using low-level routines in vmBaseLib. You can make portions of memory non-cacheable, write-protect portions of memory, invalidate pages, lock TLB entries, or optimize the size of memory pages. For more information about the virtual memory routines, see the VxWorks API reference for vmBaseLib. NOTE: There are differences in the vmBaseLib library provided for the symmetric multiprocessor (SMP) and uniprocessor (UP) configurations of VxWorks, and special guidelines for its use in optimizing SMP applications. For more information about vmBaseLib and SMP, see vmBaseLib Restrictions, p.709 and Using vmBaseLib, p.701. For general information about VxWorks SMP and about migration, see 15. VxWorks SMP and 15.15 Migrating Code to VxWorks SMP, p.702. Modifying Page States Each virtual memory page (typically 4 KB) has a state associated with it. A page can be valid/invalid, readable, writable, executable, or cacheable/non-cacheable. The state of a page can be changed with the vmStateSet( ) routine. See Table 6-4 and Table 6-5 for lists of the page state constants and page state masks that can be used with vmStateSet( ). A page state mask must be used to describe which flags 346 6 Memory Management 6.9 Virtual Memory Management are being changed. A logical OR operator can be used with states and masks to define both mapping protection and cache attributes. Table 6-4 Page State Constants Constant Description MMU_ATTR_VALID Valid translation MMU_ATTR_VALID_NOT Invalid translation MMU_ATTR_PRO_SUP_READ Readable memory in kernel mode MMU_ATTR_PRO_SUP_WRITE Writable memory in kernel mode MMU_ATTR_PRO_SUP_EXE Executable memory in kernel mode MMU_ATTR_PRO_USR_READ Readable memory in user mode MMU_ATTR_PRO_USR_WRITE Writable memory in user mode MMU_ATTR_PRO_USR_EXE Executable memory in user mode MMU_ATTR_CACHE_OFF Non-cacheable memory MMU_ATTR_CACHE_COPYBACK Cacheable memory, copyback mode MMU_ATTR_CACHE_WRITETHRU Cacheable memory, writethrough mode MMU_ATTR_CACHE_DEFAULT Default cache mode (equal to either COPYBACK, WRITETHRU, or CACHE_OFF, depending on the setting of USER_D_CACHE_MODE) MMU_ATTR_CACHE_COHERENCY Memory coherency is enforced (not supported on all architectures; for more information, see the VxWorks Architecture Supplement) MMU_ATTR_CACHE_GUARDED Prevent out-of-order load operations, and pre-fetches (not supported on all architectures; for more information, see the VxWorks Architecture Supplement) MMU_ATTR_NO_BLOCK Page attributes can be changed from ISR. 6 347 VxWorks Kernel Programmer's Guide, 6.6 Table 6-4 Page State Constants (cont’d) Constant Description MMU_ATTR_SPL_0 Optional Architecture Specific States (only used by some architectures; for more information, see the VxWorks Architecture Supplement) ... MMU_ATTR_SPL_7 Table 6-5 Page State Masks Constant Description MMU_ATTR_VALID_MSK Modify valid flag MMU_ATTR_PROT_MSK Modify protection flags MMU_ATTR_CACHE_MSK Modify cache flags MMU_ATTR_SPL_MSK Modify architecture specific flags Not all combinations of protection settings are supported by all CPUs. For example, many processor types do not provide setting for execute or non-execute settings. On such processors, readable also means executable. For information about architecture-specific page states and their combination, see the VxWorks Architecture Supplement. Making Memory Non-Writable Sections of memory can be write-protected using vmStateSet( ) to prevent inadvertent access. This can be used, for example, to restrict modification of a data object to a particular routine. If a data object is global but read-only, tasks can read the object but not modify it. Any task that must modify this object must call the associated routine. Inside the routine, the data is made writable for the duration of the routine, and on exit, the memory is set to MMU_ATTR_PROT_SUP_READ. Nonwritable Memory Example In this code example, a task calls dataModify( ) to modify the data structure pointed to by pData. This routine makes the memory writable, modifies the data, and sets the memory back to nonwritable. If a task subsequently tries to modify the data without using dataModify( ), a data access exception occurs. 348 6 Memory Management 6.9 Virtual Memory Management /* privateCode.h - header file to make data writable from routine only */ #define MAX 1024 typedef struct myData { char stuff[MAX]; int moreStuff; } MY_DATA; /* privateCode.c - uses VM contexts to make data private to a code segment */ #include #include #include #include #include "privateCode.h" MY_DATA * pData; SEM_ID dataSemId; int pageSize; /*********************************************************************** * * initData - allocate memory and make it nonwritable * * This routine initializes data and should be called only once. * */ STATUS initData (void) { pageSize = vmPageSizeGet(); /* create semaphore to protect data */ dataSemId = semBCreate (SEM_Q_PRIORITY, SEM_EMPTY); /* allocate memory = to a page */ pData = (MY_DATA *) valloc (pageSize); /* initialize data and make it read-only */ bzero ((char *) pData, pageSize); if (vmStateSet (NULL, (VIRT_ADDR) pData, pageSize, MMU_ATTR_PROT_MSK, MMU_ATTR_PROT_SUP_READ) == ERROR) { semGive (dataSemId); return (ERROR); } /* release semaphore */ semGive (dataSemId); return (OK); } /******************************************************************** * * dataModify - modify data * * To modify data, tasks must call this routine, passing a pointer to * the new data. * To test from the shell use: * -> initData * -> sp dataModify * -> d pData * -> bfill (pdata, 1024, ‘X’) */ 349 6 VxWorks Kernel Programmer's Guide, 6.6 STATUS dataModify ( MY_DATA * pNewData ) { /* take semaphore for exclusive access to data */ semTake (dataSemId, WAIT_FOREVER); /* make memory writable */ if (vmStateSet (NULL, (VIRT_ADDR) pData, pageSize, MMU_ATTR_PROT_MSK, MMU_ATTR_PROT_SUP_READ | MMU_ATTR_PROT_SUP_WRITE) == ERROR) { semGive (dataSemId); return (ERROR); } /* update data*/ bcopy ((char *) pNewData, (char *) pData, sizeof(MY_DATA)); /* make memory not writable */ if (vmStateSet (NULL, (VIRT_ADDR) pData, pageSize, MMU_ATTR_PROT_MSK, MMU_ATTR_PROT_SUP_READ) == ERROR) { semGive (dataSemId); return (ERROR); } semGive (dataSemId); return (OK); } Invalidating Memory Pages To invalidate memory on a page basis, use vmStateSet( ) as follows: vmStateSet (NULL, address, len, MMU_ATTR_VALID_MSK, MMU_ATTR_VALID_NOT); Any access to a mapping made invalid generates an exception whether it is a read or a write access. To re-validate the page, use vmStateSet( ) as follows: vmStateSet (NULL, address, len, MMU_ATTR_VALID_MSK, MMU_ATTR_VALID); Locking TLB Entries For some processors it is possible to force individual entries in the Translation Look-aside Buffer (TLB) to remain permanently in the TLB. When the architecture-specific MMU library supports this feature, the vmPageLock( ) routine can be used to lock page entries, and vmPageUnlock( ) to unlock page entries. 350 6 Memory Management 6.9 Virtual Memory Management The INCLUDE_LOCK_TEXT_SECTION component provides facilities for TLB locking. When this component is included in VxWorks, the kernel image text section is automatically locked at system startup. This feature can be used for performance optimizations in a manner similar to cache locking. When often-used page entries are locked in the TLB, the number of TLB misses can be reduced. Note that the number of TLB entries are generally limited on all processors types, so locking too many entries can result in contention for the remaining entries that are used dynamically. For more information, see the VxWorks Architecture Supplement. Page Size Optimization For some processors it is possible to enable larger page sizes than the default (defined by VM_PAGE_SIZE) for large, contiguous memory blocks that have homogeneous memory attributes. There are several advantages to using such optimization, including: ■ Reducing the number of page table entries (PTE) needed to map memory, resulting in less memory used. ■ More efficient TLB entry usage, resulting in fewer TLB misses, therefore potentially better performance. Optimization of the entire kernel memory space (including I/O blocks) at startup can be accomplished by configuring VxWorks with the INCLUDE_PAGE_SIZE_OPTIMIZATION component. Page size optimization for specific blocks of memory can be accomplished at run-time with the vmPageOptimize( ) routine. De-optimization is performed automatically when necessary. For example, if part of a memory block that has been optimized is set with different attributes, the large page is automatically broken up into multiple smaller pages and the new attribute is set to the requested pages only. Setting Page States in ISRs For many types of processors, vmStateSet( ) is a non-blocking routine, and can therefore be called safely from ISRs. However, it may block in some cases, such as on processors that support page size optimization (see Page Size Optimization, p.351). 351 6 VxWorks Kernel Programmer's Guide, 6.6 To make sure that vmStateSet( ) can be called safely from an ISR for specific pages, the page must first have the MMU_ATTR_NO_BLOCK attribute set. The following code example shows how this can be done: #include #include #define DATA_SIZE 0x10000 char * pData; void someInitFunction () { /* allocate buffer */ pData = (char *) valloc (DATA_SIZE); /* set no-block attribute for the buffer */ vmStateSet (NULL, (VIRT_ADDR) pData, DATA_SIZE, MMU_ATTR_SPL_MSK, MMU_ATTR_NO_BLOCK); } void someISR () { ... /* now it's safe to set any attribute for the buffer in an ISR */ vmStateSet (NULL, (VIRT_ADDR) pData, DATA_SIZE, MMU_ATTR_PROT_MSK, MMU_ATTR_SUP_RWX); ... } 6.9.3 Troubleshooting The show routines and commands described in Table 6-6 are available to assist with trouble-shooting virtual memory problems. 352 6 Memory Management 6.10 Additional Memory Protection Features Table 6-6 Virtual Memory Shell Commands C Interpreter Command Interpreter Description vmContextShow( ) vm context Lists information about the entire process context, including private mappings and kernel mappings (for supervisor access), as well as any shared data contexts attached to the process. rtpMemShow( ) rtp meminfo Lists only the process’ private mappings. These routines and commands are provided by the INCLUDE_VM_SHOW, INCLUDE_VM_SHOW_SHELL_CMD, INCLUDE_RTP_SHOW, and INCLUDE_RTP_SHOW_SHELL_CMD components. For more details and usage example of the show routines see the VxWorks shell references. 6.10 Additional Memory Protection Features VxWorks provides MMU-based features that supplement basic virtual memory support to provide a more reliable run-time environment. These additional memory-protection features are: ■ ■ ■ ■ ■ task stack overrun and underrun detection interrupt stack overrun and underrun detection non-executable task stacks text segment write-protection exception vector table write-protection For information about basic virtual memory support, see 6.9 Virtual Memory Management, p.343. Errors generated with the use of these features can be detected and managed with additional VxWorks facilities. See 11. Error Detection and Reporting for more information. 353 6 VxWorks Kernel Programmer's Guide, 6.6 6.10.1 Configuring VxWorks for Additional Memory Protection The components listed in Table 6-7 provide additional memory-protection features. They can be added to VxWorks as a unit with the INCLUDE_KERNEL_HARDENING component. The individual and composite components all include the basic virtual memory component INCLUDE_MMU_BASIC by default. Table 6-7 Additional Memory Protection Components Component Description INCLUDE_PROTECT_TASK_STACK Task stack overrun and underrun protection. INCLUDE_TASK_STACK_NO_EXEC Non-executable task stacks. INCLUDE_PROTECT_TEXT Text segment write-protection. INCLUDE_PROTECT_VEC_TABLE Exception vector table write-protection and NULL pointer reference detection. INCLUDE_PROTECT_INTERRUPT_STACK Interrupt stack overrun and underrun protection. Note that protection of the kernel text segment—and the text segments of kernel modules dynamically loaded into the kernel space—is not provided by default. On the other hand, the text segment of processes and shared libraries is always write-protected, whether or not VxWorks is configured with the INCLUDE_PROTECT_TEXT component. Similarly, the execution stack of a process task is not affected by the INCLUDE_PROTECT_TASK_STACK or INCLUDE_TASK_STACK_NO_EXEC components—it is always protected unless the task is spawned with the taskSpawn( ) option VX_NO_STACK_PROTECT. 6.10.2 Stack Overrun and Underrun Detection VxWorks can be configured so that guard zones are inserted at the beginning and end of task execution stacks. For more information, see Task Stack Guard Zones, p.176. The operating system can also be configured to insert guard zones at both ends of the interrupt stack. For more information, see Interrupt Stack Protection, p.243. 354 6 Memory Management 6.11 Processes Without MMU Support 6.10.3 Non-Executable Task Stack VxWorks can be configured so that task stacks are non-executable. For more information, see Non-Executable Task Stacks, p.177. 6.10.4 Text Segment Write Protection All text segments are write-protected when VxWorks is configured with the INCLUDE_PROTECT_TEXT component. When VxWorks is loaded, all text segments are write-protected The text segments of any additional object modules loaded in the kernel space using ld( ) are automatically marked as read-only. When object modules are loaded, memory that is to be write-protected is allocated in page-size increments. No additional steps are required to write-protect kernel application code. 6.10.5 Exception Vector Table Write Protection When VxWorks is configured with the INCLUDE_PROTECT_VEC_TABLE component, the exception vector table is write-protected during system initialization. The architecture-specific API provided to modify the vector table automatically write-enables the exception vector table for the duration of the call. For more information about these APIs, see the VxWorks Architecture Supplement for the architecture in question. 6.11 Processes Without MMU Support VxWorks can be configured to provide support for real-time processes on a system based on a processor without an MMU, or based on a processor with MMU but with the MMU disabled. With this configuration, a software simulation-based memory page management library keeps track of identity mappings only. This means that there is no address translation, and memory page attributes (protection attributes and cache attributes) are not supported. 355 6 VxWorks Kernel Programmer's Guide, 6.6 ! CAUTION: VxWorks SMP does not support MMU-less configurations. For information about VxWorks SMP, see 15. VxWorks SMP. The advantages of a configuration without MMU support are that it: ■ Enables the process environment on systems without an MMU. It provides private namespace for applications, for building applications independently from the kernel, and for simple migration from systems without an MMU to those with one. ■ Allows application code be run in non-privileged (user) mode. ■ Under certain conditions, it may provide increased performance by eliminating overhead of the TLB miss and reload. This assumes, however, that there is no negative impact due to the changed cache conditions. The limitations of this configuration are: ■ Depending on the processor type, BSP configuration, drivers and OS facilities used, disabling the MMU may require disabling the data cache as well. Disabling the data cache results in significant performance penalty that is much greater than the benefit derived from avoiding TLB misses. ■ There is no memory protection. That is, memory cannot be write-protected, and neither the kernel or any process are protected from other processes. ■ The address space is limited to the available system RAM, which is typically smaller than it would be available on systems with MMU-based address translation enabled. Because of the smaller address space, a system is more likely to run out of large contiguous blocks of memory due to fragmentation. ■ Not all processors and target boards can be used with the MMU disabled. For the requirements of your system see the hardware manual of the board and processor used. For information about architecture and processor-specific limitations, see the VxWorks Architecture Supplement. Configuring VxWorks With Process Support for Systems Without an MMU There are no special components needed for the process environment with software-simulated paging. As with any configurations that provide process support, the INCLUDE_RTP component must be added to the kernel. The steps required to enable software-simulated paging are: 356 6 Memory Management 6.11 Processes Without MMU Support 1. Add the INCLUDE_RTP component to include process support. This automatically includes all dependent subsystems, among them INCLUDE_MMU_BASIC. 2. Change the SW_MMU_ENABLE parameter of the INCLUDE_MMU_BASIC component to TRUE (the default value is FALSE). In addition, the following optional configuration steps can reduce the footprint of the system: 3. 4. Change the VM_PAGE_SIZE parameter of the INCLUDE_MMU_BASIC component. The default is architecture-dependent; usually 4K or 8K. Allowed values are 1K, 2K, 4K, 8K, 16K, 32K, 64K. Typically, a smaller page size results in finer granularity and therefore more efficient use of the memory space. However, smaller page size requires more memory needed for keeping track the mapping information. Disable stack guard page protection by changing the TASK_STACK_OVERFLOW_SIZE and TASK_STACK_UNDERFLOW_SIZE configuration parameters to zero. Without protection provided by an MMU, stack overflow and underflow cannot be detected, so the guard pages serve no purpose. 5. Remove the following components from the VxWorks configuration: INCLUDE_KERNEL_HARDENING, INCLUDE_PROTECT_TEXT, INCLUDE_PROTECT_VEC_TABLE, INCLUDE_PROTECT_TASK_STACK, INCLUDE_TASK_STACK_NO_EXEC, and INCLUDE_PROTECT_INTERRUPT_STACK. Without an MMU, these features do not work. Including them only results in unnecessary consumption of resources. 357 6 VxWorks Kernel Programmer's Guide, 6.6 358 7 I/O System 7.1 Introduction 360 7.2 Configuring VxWorks With I/O Facilities 362 7.3 Files, Devices, and Drivers 363 7.4 Basic I/O 365 7.5 Buffered I/O: stdio 378 7.6 Other Formatted I/O 380 7.7 Asynchronous Input/Output 381 7.8 Devices in VxWorks 391 7.9 Differences Between VxWorks and Host System I/O 422 7.10 Internal I/O System Structure 423 7.11 PCMCIA 450 7.12 Peripheral Component Interconnect: PCI 450 359 VxWorks Kernel Programmer's Guide, 6.6 7.1 Introduction The VxWorks I/O system is designed to present a simple, uniform, device-independent interface to any kind of device, including: ■ character-oriented devices such as terminals or communications lines ■ random-access block devices such as disks ■ virtual devices such as intertask pipes and sockets ■ monitor and control devices such as digital and analog I/O devices ■ network devices that give access to remote devices The VxWorks I/O system provides standard C libraries for both basic and buffered I/O. The basic I/O libraries are UNIX-compatible; the buffered I/O libraries are ANSI C-compatible. Internally, the VxWorks I/O system has a unique design that makes it faster and more flexible than most other I/O systems. These are important attributes in a real-time system. The diagram in Figure 7-1 illustrates the relationships between the different elements of the VxWorks I/O system. All of these elements are discussed in this chapter, except for file system routines (which are dealt with in 8. Local File Systems), and the network elements (which are covered in the Wind River Network Stack for VxWorks 6 Programmer’s Guide). 360 7 I/O System 7.1 Introduction Figure 7-1 Overview of the VxWorks I/O System Application Buffered I/O: stdio fioLib fread( ) fwrite( ) fioRead( ) printf( ) sprintf( ) Basic I/O Routines (device independent) Network Sockets Interface read( ) write( ) send( ) recv( ) Driver Routines File System Routines NetWork Stack Routines Library Routines xxRead( ) xxWrite( ) bsdSend( ) bsdReceive( ) tyLib xxRead( ) xxWrite( ) XBD Routines Hardware Devices xyzStrategy( ) Network Disk Drive Serial Device NOTE: The dotted lines in Figure 7-1 indicate that the XBD facility is required for some file systems, but not others. For example, HRFS and dosFs require XBD, while ROMFS has its own interface to drivers. See 7.8.8 Extended Block Device Facility: XBD, p.402. NOTE: This chapter provides information about facilities available in the VxWorks kernel. For information about facilities available to real-time processes, see the corresponding chapter in the VxWorks Application Programmer’s Guide. 361 7 VxWorks Kernel Programmer's Guide, 6.6 7.2 Configuring VxWorks With I/O Facilities The components providing the primary VxWorks I/O facilities are as follows: ■ INCLUDE_IO_BASIC—provides basic I/O functionality. ■ INCLUDE_IO_FILE_SYSTEM—provides file system support. ■ INCLUDE_POSIX_DIRLIB—provides POSIX directory utilities. ■ INCLUDE_POSIX_FS—provides POSIX file system APIs. ■ INCLUDE_IO_REMOVABLE—provides support for removable file systems. ■ INCLUDE_IO_POSIX—Provides POSIX I/O support. ■ INCLUDE_IO_RTP—provides I/O support for RTPs. ■ INCLUDE_IO_MISC—miscellaneous IO functions that are no longer referenced but are provided for backwards compatibility. The component INCLUDE_IO_SYSTEM is provided for backward compatibility. It includes all the components listed above. Components that provide support for additional features are described throughout this chapter. 362 7 I/O System 7.3 Files, Devices, and Drivers 7.3 Files, Devices, and Drivers In VxWorks, applications access I/O devices by opening named files. A file can refer to one of two things: ■ An unstructured raw device such as a serial communications channel or an intertask pipe. ■ A logical file on a structured, random-access device containing a file system. Consider the following named files: 7 /usr/myfile /pipe/mypipe /tyCo/0 The first refers to a file called myfile, on a disk device called /usr. The second is a named pipe (by convention, pipe names begin with /pipe). The third refers to a physical serial channel. However, I/O can be done to or from any of these in the same way. Within VxWorks, they are all called files, even though they refer to very different physical objects. Devices are handled by device drivers. In general, using the I/O system does not require any further understanding of the implementation of devices and drivers. Note, however, that the VxWorks I/O system gives drivers considerable flexibility in the way they handle each specific device. Drivers conform to the conventional user view presented here, but can differ in the specifics. See 7.8 Devices in VxWorks, p.391. Although all I/O is directed at named files, it can be done at two different levels: basic and buffered. The two differ in the way data is buffered and in the types of calls that can be made. These two levels are discussed in later sections. 7.3.1 Filenames and the Default Device A filename is specified as a character string. An unstructured device is specified with the device name. In the case of file system devices, the device name is followed by a filename. Thus, the name /tyCo/0 might name a particular serial I/O channel, and the name DEV1:/file1 indicates the file file1 on the DEV1: device. When a filename is specified in an I/O call, the I/O system searches for a device with a name that matches at least an initial substring of the filename. The I/O function is then directed at this device. 363 VxWorks Kernel Programmer's Guide, 6.6 If a matching device name cannot be found, then the I/O function is directed at a default device. You can set this default device to be any device in the system, including no device at all, in which case failure to match a device name returns an error. You can obtain the current default path by using ioDefPathGet( ). You can set the default path by using ioDefPathSet( ). Non-block devices are named when they are added to the I/O system, usually at system initialization time. Block devices are named when they are initialized for use with a specific file system. The VxWorks I/O system imposes no restrictions on the names given to devices. The I/O system does not interpret device or filenames in any way, other than during the search for matching device and filenames. It is useful to adopt some naming conventions for device and file names: most device names begin with a forward-slash (/), except non-NFS network devices, and VxWorks HRFS and dosFs file system devices. NOTE: To be recognized by the virtual root file system, device names must begin with a single leading forward-slash, and must not contain any other slash characters. For more information, see 8.3 Virtual Root File System: VRFS, p.457. By convention, NFS-based network devices are mounted with names that begin with a slash. For example: /usr Non-NFS network devices are named with the remote machine name followed by a colon. For example: host: The remainder of the name is the filename in the remote directory on the remote system. File system devices using dosFs are often named with uppercase letters and digits followed by a colon. For example: DEV1: NOTE: Filenames and directory names on dosFs devices are often separated by backslashes (\). These can be used interchangeably with forward slashes (/). ! CAUTION: Because device names are recognized by the I/O system using simple substring matching, a slash (/ or \) should not be used alone as a device name, nor should a slash be used as any part of a device name itself. 364 7 I/O System 7.4 Basic I/O 7.4 Basic I/O Basic I/O is the lowest level of I/O in VxWorks. The basic I/O interface is source-compatible with the I/O primitives in the standard C library. There are seven basic I/O calls, shown in Table 7-1. Table 7-1 Basic I/O Routines Routine Description creat( ) Creates a file. remove( ) Deletes a file. open( ) Opens a file (optionally, creates a file if it does not already exist.) close( ) Closes a file. read( ) Reads a previously created or opened file. write( ) Writes to a previously created or opened file. ioctl( ) Performs special control functions on files. 7 7.4.1 File Descriptors At the basic I/O level, files are referred to by a file descriptor. A file descriptor is a small integer returned by a call to open( ) or creat( ). The other basic I/O calls take a file descriptor as a parameter to specify a file. File descriptors are not global. The kernel has its own set of file descriptors, and each process (RTP) has its own set. Tasks within the kernel, or within a specific process share file descriptors. The only instance in which file descriptors may be shared across these boundaries, is when one process is a child of another process or of the kernel and it does not explicitly close a file using the descriptors it inherits from its parent. (Processes created by kernel tasks share only the spawning kernel task's standard I/O file descriptors 0, 1 and 2.) For example: ■ If task A and task B are running in process foo, and they each perform a write( ) on file descriptor 7, they will write to the same file (and device). ■ If process bar is started independently of process foo (it is not foo’s child) and its tasks X and Y each perform a write( ) on file descriptor 7, they will be writing to a different file than tasks A and B in process foo. 365 VxWorks Kernel Programmer's Guide, 6.6 ■ If process foobar is started by process foo (it is foo’s child) and its tasks M and N each perform a write( ) on file descriptor 7, they will be writing to the same file as tasks A and B in process foo. However, this is only true as long as the tasks do not close the file. If they close it, and subsequently open file descriptor 7 they will operate on a different file. When a file is opened, a file descriptor is allocated and returned. When the file is closed, the file descriptor is deallocated. File Descriptor Table The number of file descriptors available in the kernel is defined with the NUM_FILES configuration macro. This specifies the size of the file descriptor table, which controls how many file descriptors can be simultaneously in use. The default number is 50, but it can be changed to suit the needs of the system. To avoid running out of file descriptors, and encountering errors on file creation, applications should close any descriptors that are no longer in use. The size of the file descriptor table for the kernel can also be changed at programmatically. The rtpIoTableSizeGet( ) routine reads the size of the file descriptor table and the rtpIoTableSizeSet( ) routine changes it. Note that these routines can be used with both the kernel and processes (the I/O system treats the kernel as a special kind of process). The calling entity—whether kernel or process—can be specified with an rtpIoTableSizeSet( ) call by setting the first parameter to zero. The new size of the file descriptor table is set with the second parameter. Note that you can only increase the size. 7.4.2 Standard Input, Standard Output, and Standard Error Three file descriptors have special meanings: ■ ■ ■ 0 is used for standard input (stdin). 1 is used for standard output (stdout). 2 is used for standard error output (stderr). All tasks read their standard input—like getchar( )—from file descriptor 0. Similarly file descriptor 1 is used for standard output—like printf( ). And file descriptor 2 is used for outputting error messages. Using these descriptors, you can manipulate the input and output for many tasks at once by redirecting the files associated with the descriptors. 366 7 I/O System 7.4 Basic I/O These standard file descriptors are used to make tasks and modules independent of their actual I/O assignments. If a module sends its output to standard output (file descriptor 1), its output can then be redirected to any file or device, without altering the module. VxWorks allows two levels of redirection. First, there is a global assignment of the three standard file descriptors. Second, individual tasks can override the global assignment of these file descriptors with assignments that apply only to that task. 7.4.3 Standard I/O Redirection 7 When VxWorks is initialized, the global standard I/O file descriptors, stdin (0), stdout (1) and stderr (2), are set to the system console device file descriptor by default, which is usually the serial tty device. Each kernel task uses these global standard I/O file descriptors by default. Thus, any standard I/O operations like calls to printf( ) and getchar( ) use the global standard I/O file descriptors. Standard I/O can be redirected, however, either at the individual task level, or globally for the kernel. The standard I/O of a specific task can be changed with the ioTaskStdSet( ) routine. The parameters of this routine are the task ID of the task for which the change is to be made (0 is used for the calling task itself), the standard file descriptor to be redirected, and the file descriptor to direct it to. For example, a task can make the following call to write standard output to the fileFd file descriptor: ioTaskStdSet (0, 1, fileFd); The third argument (fileFd in this case) can be any valid open file descriptor. If it is a file system file, all the task's subsequent standard output, such as that from printf( ), is written to it. To reset the task standard I/O back to global standard I/O, the third argument can be 0, 1, or 2. The global standard I/O file descriptors can also be changed from the default setting, which affects all kernel tasks except that have had their task-specific standard I/O file descriptors changed from the global ones. Global standard I/O file descriptors are changed by calling ioGlobalStdSet( ). The parameters to this routine are the standard I/O file descriptor to be redirected, and the file descriptor to direct it to. For example: ioGlobalStdSet (1, newFd); 367 VxWorks Kernel Programmer's Guide, 6.6 This call sets the global standard output to newFd, which can be any valid open file descriptor. All tasks that do not have their individual task standard output redirected are affected by this redirection, and all their subsequent standard I/O output goes to newFd. The current settings of the global and any task's task standard I/O can be determined by calling ioGlobalStdGet( ) and ioTaskStdGet( ). For more information, see the VxWorks API references for these routines. Issues with Standard I/O Redirection Be careful with file descriptors used for task standard I/O redirection to ensure that data corruption does not occur. Before any task’s standard I/O file descriptors are closed, they should be replaced with new file descriptors with a call to ioTaskStdSet( ). If a task’s standard I/O is set with ioTaskStdSet( ), the file descriptor number is stored in that task’s memory. In some cases, this file descriptor may be closed, released by some other task or the one that opened it. Once it is released, it may be reused and opened to track a different file. Should the task holding it as a task standard I/O descriptor continue to use it for I/O, data corruption is unavoidable. As an example, consider a task spawned from a telnet or rlogin session. The task inherits the network session task's standard I/O file descriptors. If the session exits, the standard I/O file descriptors of the network session task are closed. However, the spawned task still holds those file descriptors as its task standard I/O continued with input and output to them. If the closed file descriptors are recycled and re-used by other open( ) call, however, data corruption results, perhaps with serious consequences for the system. To prevent this from happening, all spawned tasks must have their standard I/O file descriptors redirected before the network session is terminated. The following example illustrates this scenario, with redirection of a spawned task’s standard I/O to the global standard I/O from the shell before logout. The taskspawn( ) call is abbreviated to simplify presentation. -> taskSpawn "someTask",...... Task spawned: id = 0x52a010, name = t4 value = 5414928 = 0x52a010 -> ioTaskStdSet 0x52a010,0,0 value = 0 = 0x0 -> ioTaskStdSet 0x52a010,1,1 value = 0 = 0x0 -> ioTaskStdSet 0x52a010,2,2 value = 0 = 0x0 -> logout 368 7 I/O System 7.4 Basic I/O The next example illustrates task standard I/O redirection to other file descriptors. -> taskSpawn "someTask",...... Task spawned: id = 0x52a010, name = t4 value = 5414928 = 0x52a010 -> ioTaskStdSet 0x52a010,0,someOtherFdx value = 0 = 0x0 -> ioTaskStdSet 0x52a010,1,someOtherFdy value = 0 = 0x0 -> ioTaskStdSet 0x52a010,2,someOtherFdz value = 0 = 0x0 -> logout 7 7.4.4 Open and Close Before I/O can be performed on a device, a file descriptor must be opened to the device by invoking the open( ) routine—or creat( ), as discussed in the next section. The arguments to open( ) are the filename, the type of access, and the mode (file permissions): fd = open ("name", flags, mode); For open( ) calls made in the kernel, the mode parameter can be set to zero if file permissions do not need to be specified. The file-access options that can be used with the flags parameter to open( ) are listed in Table 7-2. Table 7-2 File Access Options Flag Description O_RDONLY Open for reading only. O_WRONLY Open for writing only. O_RDWR Open for reading and writing. O_CREAT Create a file if it does not already exist. O_EXCL Error on open if the file exists and O_CREAT is also set. O_SYNC Write on the file descriptor complete as defined by synchronized I/O file integrity completion. 369 VxWorks Kernel Programmer's Guide, 6.6 Table 7-2 ! File Access Options (cont’d) Flag Description O_DSYNC Write on the file descriptor complete as defined by synchronized I/O data integrity completion. O_RSYNC Read on the file descriptor complete at the same sync level as O_DSYNC and O_SYNC flags. O_APPEND Set the file offset to the end of the file prior to each write, which guarantees that writes are made at the end of the file. It has no effect on devices other than the regular file system. O_NONBLOCK Non-blocking I/O. O_NOCTTY If the named file is a terminal device, don't make it the controlling terminal for the process. O_TRUNC Open with truncation. If the file exists and is a regular file, and the file is successfully opened, its length is truncated to 0. It has no effect on devices other than the regular file system. WARNING: While the third parameter to open( )—mode, for file permissions—is usually optional for other operating systems, it is required for the VxWorks implementation of open( ) in the kernel (but not in processes). When the mode parameter is not appropriate for a given call, it should be set to zero. Note that this can be an issue when porting software from UNIX to VxWorks. Note the following special cases with regard to use of the file access and mode (file permissions) parameters to open( ): ■ In general, you can open only preexisting devices and files with open( ). However, with NFS network, dosFs, and HRFS devices, you can also create files with open( ) by OR’ing O_CREAT with one of the other access flags. ■ HRFS directories can be opened with the open( ) routine, but only using the O_RDONLY flag. ■ With both dosFs and NFS devices, you can use the O_CREAT flag to create a subdirectory by setting mode to FSTAT_DIR. Other uses of the mode parameter with dosFs devices are ignored. 370 7 I/O System 7.4 Basic I/O ■ With an HRFS device you cannot use the O_CREAT flag and the FSTAT_DIR mode option to create a subdirectory. HRFS ignores the mode option and simply creates a regular file. ■ The netDrv default file system does not support the F_STAT_DIR mode option or the O_CREAT flag. ■ For NFS devices, the third parameter to open( ) is normally used to specify the mode of the file. For example: myFd = open ("fooFile", O_CREAT | O_RDWR, 0644); ■ While HRFS supports setting the permission mode for a file, it is not used by the VxWorks operating system. ■ Files can be opened with the O_SYNC flag, indicating that each write should be immediately written to the backing media. This flag is currently supported by the dosFs file system, and includes synchronizing the FAT and the directory entries. ■ The O_SYNC flag has no effect with HRFS because file system is always synchronous. HRFS updates files as though the O_SYNC flag were set. NOTE: Drivers or file systems may or may not honor the flag values or the mode values. A file opened with O_RDONLY mode may in fact be writable if the driver allows it. Consult the driver or file system information for specifics. See the VxWorks file system API references for more information about the features that each file system supports. The open( ) routine, if successful, returns a file descriptor. This file descriptor is then used in subsequent I/O calls to specify that file. The file descriptor is an identifier that is not task specific; that is, it is shared by all tasks within the memory space. Within a given process or the kernel, therefore, one task can open a file and any other task can then use the file descriptor. The file descriptor remains valid until close( ) is invoked with that file descriptor, as follows: close (fd); At that point, I/O to the file is flushed (completely written out) and the file descriptor can no longer be used by any task within the process (or kernel). However, the same file descriptor number can again be assigned by the I/O system in any subsequent open( ). Since the kernel only terminates when the system shuts down, there is no situation analogous to file descriptors being closed automatically when a process terminates. File descriptors in the kernel can only be closed by direct command. 371 7 VxWorks Kernel Programmer's Guide, 6.6 7.4.5 Create and Remove File-oriented devices must be able to create and remove files as well as open existing files. The creat( ) routine directs a file-oriented device to make a new file on the device and return a file descriptor for it. The arguments to creat( ) are similar to those of open( ) except that the filename specifies the name of the new file rather than an existing one; the creat( ) routine returns a file descriptor identifying the new file. fd = creat ("name", flag); Note that with the HRFS file system the creat( ) routine is POSIX-compliant, and the second parameter is used to specify file permissions; the file is opened in O_RDWR mode. With dosFs, however, the creat( ) routine is not POSIX-compliant and the second parameter is used for open mode flags. The remove( ) routine deletes a named file on a file-system device: remove ("name"); Files should be closed before they are removed. With non-file-system devices, the creat( ) routine performs the same function as open( ). The remove( ) routine, however has no effect. 7.4.6 Read and Write After a file descriptor is obtained by invoking open( ) or creat( ), tasks can read bytes from a file with read( ) and write bytes to a file with write( ). The arguments to read( ) are the file descriptor, the address of the buffer to receive input, and the maximum number of bytes to read: nBytes = read (fd, &buffer, maxBytes); The read( ) routine waits for input to be available from the specified file, and returns the number of bytes actually read. For file-system devices, if the number of bytes read is less than the number requested, a subsequent read( ) returns 0 (zero), indicating end-of-file. For non-file-system devices, the number of bytes read can be less than the number requested even if more bytes are available; a subsequent read( ) may or may not return 0. In the case of serial devices and TCP sockets, repeated calls to read( ) are sometimes necessary to read a specific number of bytes. (See the reference entry for fioRead( ) in fioLib). A return value of ERROR (-1) indicates an unsuccessful read. 372 7 I/O System 7.4 Basic I/O The arguments to write( ) are the file descriptor, the address of the buffer that contains the data to be output, and the number of bytes to be written: actualBytes = write (fd, &buffer, nBytes); The write( ) routine ensures that all specified data is at least queued for output before returning to the caller, though the data may not yet have been written to the device (this is driver dependent). The write( ) routine returns the number of bytes written; if the number returned is not equal to the number requested, an error has occurred. 7 7.4.7 File Truncation It is sometimes convenient to discard part of the data in a file. After a file is open for writing, you can use the ftruncate( ) routine to truncate a file to a specified size. Its arguments are a file descriptor and the desired length of the file in bytes: status = ftruncate (fd, length); If it succeeds in truncating the file, ftruncate( ) returns OK. If the file descriptor refers to a device that cannot be truncated, ftruncate( ) returns ERROR, and sets errno to EINVAL. If the size specified is larger than the actual size of the file, the result depends on the file system. For both dosFs and HRFS, the size of the file is extended to the specified size; however, for other file systems, ftruncate( ) returns ERROR, and sets errno to EINVAL (just as if the file descriptor referred to a device that cannot be truncated). The ftruncate( ) routine is part of the POSIX 1003.1b standard. It is fully supported as such by the HRFS. The dosFs implementation is, however, only partially compliant: creation and modification times are not changed. Also note that with HRFS the seek position is not modified by truncation, but with dosFs the seek position is set to the end of the file. 7.4.8 I/O Control The ioctl( ) routine provides a flexible mechanism for performing I/O functions that are not performed by the other basic I/O calls. Examples include determining how many bytes are currently available for input, setting device-specific options, obtaining information about a file system, and positioning random-access files to specific byte positions. 373 VxWorks Kernel Programmer's Guide, 6.6 The arguments to the ioctl( ) routine are the file descriptor, a code that identifies the control function requested, and an optional function-dependent argument: result = ioctl (fd, function, arg); For example, the following call uses the FIOBAUDRATE function to set the baud rate of a tty device to 9600: status = ioctl (fd, FIOBAUDRATE, 9600); The discussion of specific devices in 7.8 Devices in VxWorks, p.391 summarizes the ioctl( ) functions available for each device. The ioctl( ) control codes are defined in ioLib.h. For more information, see the reference entries for specific device drivers or file systems. 7.4.9 Pending on Multiple File Descriptors with select( ) The VxWorks select facility provides a UNIX- and Windows-compatible method for pending on multiple file descriptors. The library selectLib provides both task-level support, allowing tasks to wait for multiple devices to become active, and device driver support, giving drivers the ability to detect tasks that are pended while waiting for I/O on the device. To use this facility, the header file selectLib.h must be included in your application code. Task-level support not only gives tasks the ability to simultaneously wait for I/O on multiple devices, but it also allows tasks to specify the maximum time to wait for I/O to become available. An example of using the select facility to pend on multiple file descriptors is a client-server model, in which the server is servicing both local and remote clients. The server task uses a pipe to communicate with local clients and a socket to communicate with remote clients. The server task must respond to clients as quickly as possible. If the server blocks waiting for a request on only one of the communication streams, it cannot service requests that come in on the other stream until it gets a request on the first stream. For example, if the server blocks waiting for a request to arrive in the socket, it cannot service requests that arrive in the pipe until a request arrives in the socket to unblock it. This can delay local tasks waiting to get their requests serviced. The select facility solves this problem by giving the server task the ability to monitor both the socket and the pipe and service requests as they come in, regardless of the communication stream used. Tasks can block until data becomes available or the device is ready for writing. The select( ) routine returns when one or more file descriptors are ready or a timeout has occurred. Using the select( ) routine, a task specifies the file descriptors on which to wait for activity. Bit fields are used in the select( ) call to specify the read 374 7 I/O System 7.4 Basic I/O and write file descriptors of interest. When select( ) returns, the bit fields are modified to reflect the file descriptors that have become available. The macros for building and manipulating these bit fields are listed in Table 7-3. Table 7-3 Select Macros Macro Description FD_ZERO Zeroes all bits. FD_SET Sets the bit corresponding to a specified file descriptor. FD_CLR Clears a specified bit. FD_ISSET Returns non-zero if the specified bit is set; otherwise returns 0. Applications can use select( ) with any character I/O devices that provide support for this facility (for example, pipes, serial devices, and sockets). For information on writing a device driver that supports select( ), see Implementing select( ), p.441. 375 7 VxWorks Kernel Programmer's Guide, 6.6 Example 7-1 Using select( ) /* selServer.c - select example * In this example, a server task uses two pipes: one for normal-priority * requests, the other for high-priority requests. The server opens both * pipes and blocks while waiting for data to be available in at least one * of the pipes. */ #include #include #include #define #define #define #define MAX_FDS 2 MAX_DATA 1024 PIPEHI "/pipe/highPriority" PIPENORM "/pipe/normalPriority" /************************************************************************ * selServer - reads data as it becomes available from two different pipes * * Opens two pipe fds, reading from whichever becomes available. The * server code assumes the pipes have been created from either another * task or the shell. To test this code from the shell do the following: * -> ld < selServer.o * -> pipeDevCreate ("/pipe/highPriority", 5, 1024) * -> pipeDevCreate ("/pipe/normalPriority", 5, 1024) * -> fdHi = open ("/pipe/highPriority", 1, 0) * -> fdNorm = open ("/pipe/normalPriority", 1, 0) * -> iosFdShow * -> sp selServer * -> i * At this point you should see selServer’s state as pended. You can now * write to either pipe to make the selServer display your message. * -> write fdNorm, "Howdy", 6 * -> write fdHi, "Urgent", 7 */ STATUS selServer (void) { struct fd_set readFds; int fds[MAX_FDS]; int width; int i; char buffer[MAX_DATA]; /* /* /* /* /* bit mask of fds to read from */ array of fds on which to pend */ number of fds on which to pend */ index for fd array */ buffer for data that is read */ /* open file descriptors */ if ((fds[0] = open (PIPEHI, O_RDONLY, 0)) == ERROR) { close (fds[0]); return (ERROR); } if ((fds[1] = open (PIPENORM, O_RDONLY, 0)) == ERROR) 376 7 I/O System 7.4 Basic I/O { close (fds[0]); close (fds[1]); return (ERROR); } /* loop forever reading data and servicing clients */ FOREVER { /* clear bits in read bit mask */ FD_ZERO (&readFds); 7 /* initialize bit mask */ FD_SET (fds[0], &readFds); FD_SET (fds[1], &readFds); width = (fds[0] > fds[1]) ? fds[0] : fds[1]; width++; /* pend, waiting for one or more fds to become ready */ if (select (width, &readFds, NULL, NULL, NULL) == ERROR) { close (fds[0]); close (fds[1]); return (ERROR); } /* step through array and read from fds that are ready */ for (i=0; i< MAX_FDS; i++) { /* check if this fd has data to read */ if (FD_ISSET (fds[i], &readFds)) { /* typically read from fd now that it is ready */ read (fds[i], buffer, MAX_DATA); /* normally service request, for this example print it */ printf ("SELSERVER Reading from %s: %s\n", (i == 0) ? PIPEHI : PIPENORM, buffer); } } } } 377 VxWorks Kernel Programmer's Guide, 6.6 7.4.10 POSIX File System Routines The POSIX fsPxLib library provides I/O and file system routines for various file manipulations. These routines are described in Table 7-4. Table 7-4 File System Routines Routine Description unlink( ) Unlink a file. link( ) Link a file. fsync( ) Synchronize a file. fdatasync( ) Synchronize the data of a file. rename( ) Change the name of a file. fpathconf( ) Determine the current value of a configurable limit. pathconf( ) Determine the current value of a configurable limit. access( ) Determine accessibility of a file. chmod( ) Change the permission mode of a file. fcntl( ) Perform control functions over open files. For more information, see the API references for fsPxLib and ioLib. 7.5 Buffered I/O: stdio The VxWorks I/O library provides a buffered I/O package that is compatible with the UNIX and Windows stdio package, and provides full ANSI C support. Configure VxWorks with the ANSI Standard component bundle to provide buffered I/O support. 378 7 I/O System 7.5 Buffered I/O: stdio NOTE: The implementation of printf( ), sprintf( ), and sscanf( ), traditionally considered part of the stdio package, is part of a different package in VxWorks. These routines are discussed in 7.6 Other Formatted I/O, p.380. 7.5.1 Using stdio Although the VxWorks I/O system is efficient, some overhead is associated with each low-level call. First, the I/O system must dispatch from the device-independent user call (read( ), write( ), and so on) to the driver-specific routine for that function. Second, most drivers invoke a mutual exclusion or queuing mechanism to prevent simultaneous requests by multiple users from interfering with each other. This overhead is quite small because the VxWorks primitives are fast. However, an application processing a single character at a time from a file incurs that overhead for each character if it reads each character with a separate read( ) call: n = read (fd, &char, 1); To make this type of I/O more efficient and flexible, the stdio package implements a buffering scheme in which data is read and written in large chunks and buffered privately. This buffering is transparent to the application; it is handled automatically by the stdio routines and macros. To access a file with stdio, a file is opened with fopen( ) instead of open( ) (many stdio calls begin with the letter f): fp = fopen ("/usr/foo", "r"); The returned value, a file pointer is a handle for the opened file and its associated buffers and pointers. A file pointer is actually a pointer to the associated data structure of type FILE (that is, it is declared as FILE *). By contrast, the low-level I/O routines identify a file with a file descriptor, which is a small integer. In fact, the FILE structure pointed to by the file pointer contains the underlying file descriptor of the open file. A file descriptor that is already open can be associated subsequently with a FILE buffer by calling fdopen( ): fp = fdopen (fd, "r"); After a file is opened with fopen( ), data can be read with fread( ), or a character at a time with getc( ), and data can be written with fwrite( ), or a character at a time with putc( ). The routines and macros to get data into or out of a file are extremely efficient. They access the buffer with direct pointers that are incremented as data is read or 379 7 VxWorks Kernel Programmer's Guide, 6.6 written by the user. They pause to call the low-level read or write routines only when a read buffer is empty or a write buffer is full. ! WARNING: The stdio buffers and pointers are private to a particular task. They are not interlocked with semaphores or any other mutual exclusion mechanism, because this defeats the point of an efficient private buffering scheme. Therefore, multiple tasks must not perform I/O to the same stdio FILE pointer at the same time. The FILE buffer is deallocated when fclose( ) is called. 7.5.2 Standard Input, Standard Output, and Standard Error As discussed in 7.4 Basic I/O, p.365, there are three special file descriptors (0, 1, and 2) reserved for standard input, standard output, and standard error. Three corresponding stdio FILE buffers are automatically created when a task uses the standard file descriptors, stdin, stdout, and stderr, to do buffered I/O to the standard file descriptors. Each task using the standard I/O file descriptors has its own stdio FILE buffers. The FILE buffers are deallocated when the task exits. Additional routines in fioLib provide formatted but unbuffered output. The routine printErr( ) is analogous to printf( ) but outputs formatted strings to the standard error file descriptor (2). The routine fdprintf( ) outputs formatted strings to a specified file descriptor. 7.6 Other Formatted I/O This section describes additional formatting routines and facilities. 7.6.1 Special Cases: printf( ), sprintf( ), and sscanf( ) The routines printf( ), sprintf( ), and sscanf( ) are generally considered to be part of the standard stdio package. However, the VxWorks implementation of these routines, while functionally the same, does not use the stdio package. Instead, it uses a self-contained, formatted, non-buffered interface to the I/O system in the library fioLib. 380 7 I/O System 7.7 Asynchronous Input/Output Note that these routines provide the functionality specified by ANSI; however, printf( ) is not buffered. Because these routines are implemented in this way, the full stdio package, which is optional, can be omitted from a VxWorks configuration without sacrificing their availability. Applications requiring printf-style output that is buffered can still accomplish this by calling fprintf( ) explicitly to stdout. While sscanf( ) is implemented in fioLib and can be used even if stdio is omitted, the same is not true of scanf( ), which is implemented in the usual way in stdio. 7 7.6.2 Additional Routines: printErr( ) and fdprintf( ) Additional routines in fioLib provide formatted but unbuffered output. The routine printErr( ) is analogous to printf( ) but outputs formatted strings to the standard error file descriptor (2). The routine fdprintf( ) outputs formatted strings to a specified file descriptor. 7.6.3 Message Logging Another higher-level I/O facility is provided by the library logLib, which allows formatted messages to be logged without having to do I/O in the current task’s context, or when there is no task context. The message format and parameters are sent on a message queue to a logging task, which then formats and outputs the message. This is useful when messages must be logged from interrupt level, or when it is desirable not to delay the current task for I/O or use the current task’s stack for message formatting (which can take up significant stack space). The message is displayed on the console unless otherwise redirected at system startup using logInit( ) or dynamically using logFdSet( ). 7.7 Asynchronous Input/Output Asynchronous Input/Output (AIO) is the ability to perform input and output operations concurrently with ordinary internal processing. AIO enables you to de-couple I/O operations from the activities of a particular task when these are logically independent. 381 VxWorks Kernel Programmer's Guide, 6.6 The VxWorks AIO implementation meets the specification in the POSIX 1003.1b standard. The benefit of AIO is greater processing efficiency: it permits I/O operations to take place whenever resources are available, rather than making them await arbitrary events such as the completion of independent operations. AIO eliminates some of the unnecessary blocking of tasks that is caused by ordinary synchronous I/O; this decreases contention for resources between input/output and internal processing, and expedites throughput. Include AIO in your VxWorks configuration with the INCLUDE_POSIX_AIO and INCLUDE_POSIX_AIO_SYSDRV components. The second configuration constant enables the auxiliary AIO system driver, required for asynchronous I/O on all current VxWorks devices. 7.7.1 The POSIX AIO Routines The VxWorks library aioPxLib provides POSIX AIO routines. To access a file asynchronously, open it with the open( ) routine, like any other file. Thereafter, use the file descriptor returned by open( ) in calls to the AIO routines. The POSIX AIO routines (and two associated non-POSIX routines) are listed in Table 7-5. The default VxWorks initialization code calls aioPxLibInit( ) automatically when the POSIX AIO component is included in VxWorks with INCLUDE_POSIX_AIO. The aioPxLibInit( ) routine takes one parameter, the maximum number of lio_listio( ) calls that can be outstanding at one time. By default this parameter is MAX_LIO_CALLS. When the parameter is 0 (the default), the value is taken from AIO_CLUST_MAX (defined in installDir/vxworks-6.x/target/h/private/aioPxLibP.h). The AIO system driver, aioSysDrv, is initialized by default with the routine aioSysInit( ) when both INCLUDE_POSIX_AIO and INCLUDE_POSIX_AIO_SYSDRV are included in VxWorks. The purpose of aioSysDrv is to provide request queues independent of any particular device driver, so that you can use any VxWorks device driver with AIO. 382 7 I/O System 7.7 Asynchronous Input/Output Table 7-5 Asynchronous Input/Output Routines Function Description aioPxLibInit( ) Initializes the AIO library (non-POSIX). aioShow( ) Displays the outstanding AIO requests (non-POSIX).a aio_read( ) Initiates an asynchronous read operation. aio_write( ) Initiates an asynchronous write operation. lio_listio( ) Initiates a list of up to LIO_MAX asynchronous I/O requests. aio_error( ) Retrieves the error status of an AIO operation. aio_return( ) Retrieves the return status of a completed AIO operation. aio_cancel( ) Cancels a previously submitted AIO operation. aio_suspend( ) Waits until an AIO operation is done, interrupted, or timed out. aio_fsync( ) Asynchronously forces file synchronization. 7 a. This function is not built into the host shell. To use it from the host shell, VxWorks must be configured with the INCLUDE_POSIX_AIO_SHOW component. When you invoke the function, its output is sent to the standard output device. The routine aioSysInit( ) takes three parameters: the number of AIO system tasks to spawn, and the priority and stack size for these system tasks. The number of AIO system tasks spawned equals the number of AIO requests that can be handled in parallel. The default initialization call uses three constants: MAX_AIO_SYS_TASKS, AIO_TASK_PRIORITY, and AIO_TASK_STACK_SIZE. When any of the parameters passed to aioSysInit( ) is 0, the corresponding value is taken from AIO_IO_TASKS_DFLT, AIO_IO_PRIO_DFLT, and AIO_IO_STACK_DFLT (all defined in installDir/vxworks-6.x/target/h/aioSysDrv.h). Table 7-6 lists the names of the constants, and shows the constants used within initialization routines when the parameters are left at their default values of 0, and where these constants are defined. 383 VxWorks Kernel Programmer's Guide, 6.6 Table 7-6 Init Routine AIO Initialization Functions and Related Constants Configuration Parameter Def. Header File Constant Value used when arg = 0 Def. Value Header File aioPxLibInit( ) MAX_LIO_CALLS 0 AIO_CLUST_MAX 100 aioSysInit( ) MAX_AIO_SYS_TASKS 0 AIO_IO_TASKS_DFLT 2 aioSysDrv.h AIO_TASK_PRIORITY 0 AIO_IO_PRIO_DFLT 50 aioSysDrv.h AIO_TASK_STACK_SIZE 0 AIO_IO_STACK_DFLT private/aioPxLibP.h 0x7000 aioSysDrv.h 7.7.2 AIO Control Block Each of the AIO calls takes an AIO control block (aiocb) as an argument. The calling routine must allocate space for the aiocb, and this space must remain available for the duration of the AIO operation. (Thus the aiocb must not be created on the task's stack unless the calling routine will not return until after the AIO operation is complete and aio_return( ) has been called.) Each aiocb describes a single AIO operation. Therefore, simultaneous asynchronous I/O operations using the same aiocb are not valid and produce undefined results. The aiocb structure is defined in aio.h. It contains the following fields: aio_fildes The file descriptor for I/O. aio_offset The offset from the beginning of the file. aio_buf The address of the buffer from/to which AIO is requested. aio_nbytes The number of bytes to read or write. aio_reqprio The priority reduction for this AIO request. aio_sigevent The signal to return on completion of an operation (optional). aio_lio_opcode An operation to be performed by a lio_listio( ) call. 384 7 I/O System 7.7 Asynchronous Input/Output aio_sys The address of VxWorks-specific data (non-POSIX). For full definitions and important additional information, see the reference entry for aioPxLib. ! CAUTION: The aiocb structure and the data buffers referenced by it are used by the system to perform the AIO request. Therefore, once the aiocb has been submitted to the system, the application must not modify the aiocb structure until after a subsequent call to aio_return( ). The aio_return( ) call retrieves the previously submitted AIO data structures from the system. After the aio_return( ) call, the calling application can modify the aiocb, free the memory it occupies, or reuse it for another AIO call. If space for the aiocb is allocated from the stack, the task should not be deleted (or complete running) until the aiocb has been retrieved from the system with an aio_return( ) call. 7.7.3 Using AIO The routines aio_read( ), aio_write( ), or lio_listio( ) initiate AIO operations. The last of these, lio_listio( ), allows you to submit a number of asynchronous requests (read and/or write) at one time. In general, the actual I/O (reads and writes) initiated by these routines does not happen immediately after the AIO request. For this reason, their return values do not reflect the outcome of the actual I/O operation, but only whether a request is successful—that is, whether the AIO routine is able to put the operation on a queue for eventual execution. After the I/O operations themselves execute, they also generate return values that reflect the success or failure of the I/O. There are two routines that you can use to get information about the success or failure of the I/O operation: aio_error( ) and aio_return( ). You can use aio_error( ) to get the status of an AIO operation (success, failure, or in progress), and aio_return( ) to obtain the return values from the individual I/O operations. Until an AIO operation completes, its error status is EINPROGRESS. To cancel an AIO operation, call aio_cancel( ). To force all I/O operations to the synchronized I/O completion state, use aio_fsync( ). AIO with Periodic Checks for Completion The following code uses a pipe for the asynchronous I/O operations. The example creates the pipe, submits an AIO read request, verifies that the read request is still in progress, and submits an AIO write request. Under normal circumstances, a 385 7 VxWorks Kernel Programmer's Guide, 6.6 synchronous read to an empty pipe blocks and the task does not execute the write, but in the case of AIO, we initiate the read request and continue. After the write request is submitted, the example task loops, checking the status of the AIO requests periodically until both the read and write complete. Because the AIO control blocks are on the stack, we must call aio_return( ) before returning from aioExample( ). Example 7-2 Asynchronous I/O /* aioEx.c - example code for using asynchronous I/O */ /* includes */ #include #include #include #include #include #include /* defines */ #define BUFFER_SIZE 200 struct aiocb struct aiocb aiocb_read; /* read aiocb */ aiocb_write; /* write aiocb */ /************************************************************************ * aioExample - use AIO library * This example shows the basic functions of the AIO library. * RETURNS: OK if successful, otherwise ERROR. */ STATUS aioExample (const char *exFile) { int fd; char buffer [BUFFER_SIZE]; /* buffer for read aiocb */ static char * test_string = "testing 1 2 3"; int error; if ((fd = open (exFile, O_CREAT | O_TRUNC | O_RDWR, 0666)) == ERROR) { printf ("aioExample: cannot open %s for writing. errno 0x%x\n", exFile, errno); return (ERROR); } printf ("aioExample: Example file = %s\tFile descriptor = %d\n", exFile, fd); /* initialize read and write aiocbs */ 386 7 I/O System 7.7 Asynchronous Input/Output memset ( &aiocb_read, 0, sizeof (struct aiocb)); memset ( buffer, 0, sizeof (buffer)); aiocb_read.aio_fildes = fd; aiocb_read.aio_buf = buffer; aiocb_read.aio_nbytes = BUFFER_SIZE; aiocb_read.aio_reqprio = 0; memset ( &aiocb_write, 0, sizeof (struct aiocb)); aiocb_write.aio_fildes = fd; aiocb_write.aio_buf = test_string; aiocb_write.aio_nbytes = strlen (test_string); aiocb_write.aio_reqprio = 0; 7 /* initiate the read */ if (aio_read (&aiocb_read) == -1) printf ("aioExample: aio_read failed\n"); /* verify that it is in progress */ if (aio_error (&aiocb_read) == EINPROGRESS) printf ("aioExample: read is still in progress\n"); /* write to pipe - the read should be able to complete */ printf ("aioExample: getting ready to initiate the write\n"); if (aio_write (&aiocb_write) == -1) printf ("aioExample: aio_write failed\n"); /* wait til both read and write are complete */ while ((error = aio_error (&aiocb_read) == EINPROGRESS) || (aio_error (&aiocb_write) == EINPROGRESS)) sleep (1); printf ("aioExample: error = %d\n", error); /* print out what was read */ printf ("aioExample: message = %s\n", buffer); /* clean up */ if (aio_return (&aiocb_read) == -1) printf ("aioExample: aio_return for aiocb_read failed\n"); if (aio_return (&aiocb_write) == -1) printf ("aioExample: aio_return for aiocb_write failed\n"); close (fd); return (OK); } 387 VxWorks Kernel Programmer's Guide, 6.6 Alternatives for Testing AIO Completion A task can determine whether an AIO request is complete in any of the following ways: ■ Check the result of aio_error( ) periodically, as in the previous example, until the status of an AIO request is no longer EINPROGRESS. ■ Use aio_suspend( ) to suspend the task until the AIO request is complete. ■ Use signals to be informed when the AIO request is complete. The following example is similar to the preceding aioExample( ), except that it uses signals for notification that the write operation has finished. If you test this from the shell, spawn the routine to run at a lower priority than the AIO system tasks to assure that the test routine does not block completion of the AIO request. Example 7-3 Asynchronous I/O with Signals #include #include #include #include #include #include /* defines */ #define #define #define #define BUFFER_SIZE 200 LIST_SIZE 1 WRITE_EXAMPLE_SIG_NO 25 /* signal number */ READ_EXAMPLE_SIG_NO 26 /* signal number */ /* forward declarations */ void writeSigHandler (int sig, struct siginfo * info, void * pContext); void readSigHandler (int sig, struct siginfo * info, void * pContext); static static static static static struct struct struct struct char aiocb aiocb sigaction sigaction aiocb_read; /* read aiocb */ aiocb_write; /* write aiocb */ write_action; /* signal info */ read_action; /* signal info */ buffer [BUFFER_SIZE]; /* aiocb read buffer */ /************************************************************************ * aioExampleSig - use AIO library. * * This example shows the basic functions of the AIO library. * Note if this is run from the shell it must be spawned. Use: * -> sp aioExampleSig * * RETURNS: OK if successful, otherwise ERROR. */ 388 7 I/O System 7.7 Asynchronous Input/Output STATUS aioExampleSig (const char *exFile) { int fd; static char * test_string = "testing 1 2 3"; if ((fd = open (exFile, O_CREAT | O_TRUNC| O_RDWR, 0666)) == ERROR) { printf ("aioExample: cannot open %s errno 0x%x\n", exFile, errno); return (ERROR); } printf ("aioExampleSig: Example file = %s\tFile descriptor = %d\n", exFile, fd); /* set up signal handler for WRITE_EXAMPLE_SIG_NO */ write_action.sa_sigaction = writeSigHandler; write_action.sa_flags = SA_SIGINFO; sigemptyset (&write_action.sa_mask); sigaction (WRITE_EXAMPLE_SIG_NO, &write_action, NULL); /* set up signal handler for READ_EXAMPLE_SIG_NO */ read_action.sa_sigaction = readSigHandler; read_action.sa_flags = SA_SIGINFO; sigemptyset (&read_action.sa_mask); sigaction (READ_EXAMPLE_SIG_NO, &read_action, NULL); /* initialize read and write aiocbs */ memset ( &aiocb_read, 0, sizeof (struct aiocb)); memset ( buffer, 0, sizeof (buffer)); aiocb_read.aio_fildes = fd; aiocb_read.aio_buf = buffer; aiocb_read.aio_nbytes = BUFFER_SIZE; aiocb_read.aio_reqprio = 0; /* set up signal info */ aiocb_read.aio_sigevent.sigev_signo = READ_EXAMPLE_SIG_NO; aiocb_read.aio_sigevent.sigev_notify = SIGEV_SIGNAL; aiocb_read.aio_sigevent.sigev_value.sival_ptr = (void *) &aiocb_read; memset ( &aiocb_write, 0, sizeof (struct aiocb)); aiocb_write.aio_fildes = fd; aiocb_write.aio_buf = test_string; aiocb_write.aio_nbytes = strlen (test_string); aiocb_write.aio_reqprio = 0; 389 7 VxWorks Kernel Programmer's Guide, 6.6 /* set up signal info */ aiocb_write.aio_sigevent.sigev_signo = WRITE_EXAMPLE_SIG_NO; aiocb_write.aio_sigevent.sigev_notify = SIGEV_SIGNAL; aiocb_write.aio_sigevent.sigev_value.sival_ptr = (void *) &aiocb_write; /* initiate the read */ if (aio_read (&aiocb_read) == -1) printf ("aioExampleSig: aio_read failed\n"); /* verify that it is in progress */ if (aio_error (&aiocb_read) == EINPROGRESS) printf ("aioExampleSig: read is still in progress\n"); /* write to pipe - the read should be able to complete */ printf ("aioExampleSig: getting ready to initiate the write\n"); if (aio_write (&aiocb_write) == -1) printf ("aioExampleSig: aio_write failed\n"); close (fd); return (OK); } void writeSigHandler ( int sig, struct siginfo * info, void * pContext ) { /* print out what was written */ printf ("writeSigHandler: Got signal for aio write\n"); /* write is complete so let’s do cleanup for it here */ if (aio_return (info->si_value.sival_ptr) == -1) { printf ("writeSigHandler: aio_return for aiocb_write failed\n"); } } void readSigHandler ( int sig, struct siginfo * info, void * pContext ) { /* print out what was read */ printf ("readSigHandler: Got signal for aio read\n"); 390 7 I/O System 7.8 Devices in VxWorks /* write is complete so let’s do cleanup for it here */ if (aio_return (info->si_value.sival_ptr) == -1) { printf ("readSigHandler: aio_return for aiocb_read failed\n"); } else { printf ("aioExample: message = %s\n", buffer); } } 7 7.8 Devices in VxWorks The VxWorks I/O system is flexible, allowing different device drivers to handle the seven basic I/O functions. All VxWorks device drivers follow the basic conventions outlined previously, but differ in specifics; this section describes those specifics. Table 7-7 Devices Provided with VxWorks Device Driver Description tty Terminal device pty Pseudo-terminal device pipe Pipe device mem Pseudo memory device nfs NFS client device net Network device for remote file access null Null device ram RAM device for creating a RAM disk scsi SCSI interface romfs ROMFS device – Other hardware-specific device 391 VxWorks Kernel Programmer's Guide, 6.6 ! WARNING: Devices should not be given the same name, or they will overwrite each other in core I/O. NOTE: Only VxBus-compatible drivers can be used with the symmetric multiprocessing (SMP) configuration of VxWorks. For general information about VxWorks SMP and about migration, see 15. VxWorks SMP and 15.15 Migrating Code to VxWorks SMP, p.702. 7.8.1 Serial I/O Devices: Terminal and Pseudo-Terminal Devices VxWorks provides terminal and pseudo-terminal devices (tty and pty). The tty device is for actual terminals; the pty device is for processes that simulate terminals. These pseudo terminals are useful in applications such as remote login facilities. VxWorks serial I/O devices are buffered serial byte streams. Each device has a ring buffer (circular buffer) for both input and output. Reading from a tty device extracts bytes from the input ring. Writing to a tty device adds bytes to the output ring. The size of each ring buffer is specified when the device is created during system initialization. NOTE: For the remainder of this section, the term tty is used to indicate both tty and pty devices tty Options The tty devices have a full range of options that affect the behavior of the device. These options are selected by setting bits in the device option word using the ioctl( ) routine with the FIOSETOPTIONS function. For example, to set all the tty options except OPT_MON_TRAP: status = ioctl (fd, FIOSETOPTIONS, OPT_TERMINAL & ~OPT_MON_TRAP); For more information, see I/O Control Functions, p.396. Table 7-8 is a summary of the available options. The listed names are defined in the header file ioLib.h. For more detailed information, see the API reference entry for tyLib. 392 7 I/O System 7.8 Devices in VxWorks Table 7-8 Tty Options Library Description OPT_LINE Selects line mode. (See Raw Mode and Line Mode, p.393.) OPT_ECHO Echoes input characters to the output of the same channel. OPT_CRMOD Translates input RETURN characters into NEWLINE (\n); translates output NEWLINE into RETURN-LINEFEED. OPT_TANDEM Responds to software flow control characters CTRL+Q and CTRL+S (XON and XOFF). OPT_7_BIT Strips the most significant bit from all input bytes. OPT_MON_TRAP Enables the special ROM monitor trap character, CTRL+X by default. OPT_ABORT Enables the special kernel shell abort character, CTRL+C by default. (Only useful if the kernel shell is configured into the system) OPT_TERMINAL Sets all of the above option bits. OPT_RAW Sets none of the above option bits. Raw Mode and Line Mode A tty device operates in one of two modes: raw mode (unbuffered) or line mode. Raw mode is the default. Line mode is selected by the OPT_LINE bit of the device option word (see tty Options, p.392). In raw mode, each input character is available to readers as soon as it is input from the device. Reading from a tty device in raw mode causes as many characters as possible to be extracted from the input ring, up to the limit of the user’s read buffer. Input cannot be modified except as directed by other tty option bits. In line mode, all input characters are saved until a NEWLINE character is input; then the entire line of characters, including the NEWLINE, is made available in the ring at one time. Reading from a tty device in line mode causes characters up to the end of the next line to be extracted from the input ring, up to the limit of the user’s read buffer. Input can be modified by the special characters CTRL+H (backspace), 393 7 VxWorks Kernel Programmer's Guide, 6.6 CTRL+U (line-delete), and CTRL+D (end-of-file), which are discussed in tty Special Characters, p.394. tty Special Characters The following special characters are enabled if the tty device operates in line mode, that is, with the OPT_LINE bit set: ■ The backspace character, by default CTRL+H, causes successive previous characters to be deleted from the current line, up to the start of the line. It does this by echoing a backspace followed by a space, and then another backspace. ■ The line-delete character, by default CTRL+U, deletes all the characters of the current line. ■ The end-of-file (EOF) character, by default CTRL+D, causes the current line to become available in the input ring without a NEWLINE and without entering the EOF character itself. Thus if the EOF character is the first character typed on a line, reading that line returns a zero byte count, which is the usual indication of end-of-file. The following characters have special effects if the tty device is operating with the corresponding option bit set: ■ The software flow control characters CTRL+Q and CTRL+S (XON and XOFF). Receipt of a CTRL+S input character suspends output to that channel. Subsequent receipt of a CTRL+Q resumes the output. Conversely, when the VxWorks input buffer is almost full, a CTRL+S is output to signal the other side to suspend transmission. When the input buffer is empty enough, a CTRL+Q is output to signal the other side to resume transmission. The software flow control characters are enabled by OPT_TANDEM. ■ The ROM monitor trap character, by default CTRL+X. This character traps to the ROM-resident monitor program. Note that this is drastic. All normal VxWorks functioning is suspended, and the computer system is controlled entirely by the monitor. Depending on the particular monitor, it may or may not be possible to restart VxWorks from the point of interruption.1 The monitor trap character is enabled by OPT_MON_TRAP. ■ The special kernel shell abort character, by default CTRL+C. This character restarts the kernel shell if it gets stuck in an unfriendly routine, such as one that 1. It will not be possible to restart VxWorks if un-handled external interrupts occur during the boot countdown. 394 7 I/O System 7.8 Devices in VxWorks has taken an unavailable semaphore or is caught in an infinite loop. The kernel shell abort character is enabled by OPT_ABORT. The characters for most of these functions can be changed using the tyLib routines shown in Table 7-9. Table 7-9 Tty Special Characters Character Description Modifier CTRL+H backspace (character delete) tyBackspaceSet( ) CTRL+U line delete tyDeleteLineSet( ) CTRL+D EOF (end of file) tyEOFSet( ) CTRL+C kernel shell abort tyAbortSet( ) CTRL+X trap to boot ROMs tyMonitorTrapSet( ) CTRL+S output suspend N/A CTRL+Q output resume N/A 395 7 VxWorks Kernel Programmer's Guide, 6.6 I/O Control Functions The tty devices respond to the ioctl( ) functions in Table 7-10, defined in ioLib.h. For more information, see the reference entries for tyLib, ttyDrv, and ioctl( ). Table 7-10 I/O Control Functions Supported by tyLib Function Description FIOBAUDRATE Sets the baud rate to the specified argument. FIOCANCEL Cancels a read or write. FIOFLUSH Discards all bytes in the input and output buffers. FIOGETNAME Gets the filename of the file descriptor. FIOGETOPTIONS Returns the current device option word. ! FIONREAD Gets the number of unread bytes in the input buffer. FIONWRITE Gets the number of bytes in the output buffer. FIOSETOPTIONS Sets the device option word. CAUTION: To change the driver’s hardware options (for example, the number of stop bits or parity bits), use the ioctl( ) function SIO_HW_OPTS_SET. Because this command is not implemented in most drivers, you may need to add it to your BSP serial driver, which resides in installDir/vxworks-6.x/target/src/drv/sio. The details of how to implement this command depend on your board’s serial chip. The constants defined in the header file installDir/vxworks-6.x/target/h/sioLib.h provide the POSIX definitions for setting the hardware options. 7.8.2 Pipe Devices Pipes are virtual devices by which tasks communicate with each other through the I/O system. Tasks write messages to pipes; these messages can then be read by other tasks. Pipe devices are managed by pipeDrv and use the kernel message queue facility to bear the actual message traffic. 396 7 I/O System 7.8 Devices in VxWorks Creating Pipes Pipes are created by calling the pipe create routine: status = pipeDevCreate ("/pipe/name", maxMsgs, maxLength); The new pipe can have at most maxMsgs messages queued at a time. Tasks that write to a pipe that already has the maximum number of messages queued are blocked until a message is dequeued. Each message in the pipe can be at most maxLength bytes long; attempts to write longer messages result in an error. 7 Writing to Pipes from ISRs VxWorks pipes are designed to allow ISRs to write to pipes in the same way as task-level code. Many VxWorks facilities cannot be used from ISRs, including output to devices other than pipes. However, ISRs can use pipes to communicate with tasks, which can then invoke such facilities. ISRs write to a pipe using the write( ) call. Tasks and ISRs can write to the same pipes. However, if the pipe is full, the message is discarded because the ISRs cannot pend. ISRs must not invoke any I/O function on pipes other than write( ). For more information ISRs, see 4.20 Interrupt Service Routines, p.241. I/O Control Functions Pipe devices respond to the ioctl( ) functions summarized in Table 7-11. The functions listed are defined in the header file ioLib.h. For more information, see the reference entries for pipeDrv and for ioctl( ) in ioLib. Table 7-11 I/O Control Functions Supported by pipeDrv Function Description FIOFLUSH Discards all messages in the pipe. FIOGETNAME Gets the pipe name of the file descriptor. FIONMSGS Gets the number of messages remaining in the pipe. FIONREAD Gets the size in bytes of the first message in the pipe. 397 VxWorks Kernel Programmer's Guide, 6.6 7.8.3 Pseudo I/O Device The memDrv device allows the I/O system to access memory directly as a pseudo-I/O device. Memory location and size are specified when the device is created. The device provides a high-level means for reading and writing bytes in absolute memory locations through I/O calls. It is useful when data must be preserved between boots of VxWorks or when sharing data between CPUs. The memDrv driver is initialized automatically by the system with memDrv( ) when the INCLUDE_USR_MEMDRV component is included in VxWorks. The call for device creation must be made from the kernel: STATUS memDevCreate (char * name, char * base, int length) Memory for the device is an absolute memory location beginning at base. The length parameter indicates the size of the memory. For additional information on the memory driver, see the memDrv( ), memDevCreate( ), and memDevCreateDir( ) entries in the VxWorks API reference, as well as the entry for memdrvbuild in the online Wind River Host Utilities API Reference. For information about creating a RAM disk, which provides support for file systems,. I/O Control Functions The memory device responds to the ioctl( ) functions summarized in Table 7-12. The functions listed are defined in the header file ioLib.h. Table 7-12 I/O Control Functions Supported by memDrv Function Description FIOSEEK Sets the current byte offset in the file. FIOWHERE Returns the current byte position in the file. For more information, see the reference entries for memDrv, ioLib, and ioctl( ). 398 7 I/O System 7.8 Devices in VxWorks 7.8.4 Network File System (NFS) Devices Network File System (NFS) devices allow files on remote hosts to be accessed with the NFS protocol. The NFS protocol specifies both client software, to read files from remote machines, and server software, to export files to remote machines. The driver nfsDrv acts as a VxWorks NFS client to access files on any NFS server on the network. VxWorks also allows you to run an NFS server to export files to other systems. Using NFS devices, you can create, open, and access remote files exactly as though they were on a file system on a local disk. This is called network transparency. For detailed information about the VxWorks implementation of NFS, see 9. Network File System: NFS. Mounting a Remote NFS File System from VxWorks Access to a remote NFS file system is established by mounting that file system locally and creating an I/O device for it using nfsMount( ). Its arguments are (1) the host name of the NFS server, (2) the name of the host file system, and (3) the local name for the file system. For example, the following call mounts /usr of the host mars as /vxusr locally: nfsMount ("mars", "/usr", "/vxusr"); This creates a VxWorks I/O device with the specified local name (/vxusr, in this example). If the local name is specified as NULL, the local name is the same as the remote name. After a remote file system is mounted, the files are accessed as though the file system were local. Thus, after the previous example, opening the file /vxusr/foo opens the file /usr/foo on the host mars. The remote file system must be exported by the system on which it actually resides. However, NFS servers can export only local file systems. Use the appropriate command on the server to see which file systems are local. NFS requires authentication parameters to identify the user making the remote access. To set these parameters, use the routines nfsAuthUnixSet( ) and nfsAuthUnixPrompt( ). To include NFS client support, use the INCLUDE_NFS component. The subject of exporting and mounting NFS file systems and authenticating access permissions is discussed in more detail in 9. Network File System: NFS. See also the 399 7 VxWorks Kernel Programmer's Guide, 6.6 reference entries nfsLib and nfsDrv, and the NFS documentation from Sun Microsystems. I/O Control Functions for NFS Clients NFS client devices respond to the ioctl( ) functions summarized in Table 7-13. The functions listed are defined in ioLib.h. For more information, see the reference entries for nfsDrv, ioLib, and ioctl( ). Table 7-13 I/O Control Functions Supported by nfsDrv Function Description FIOFSTATGET Gets file status information (directory entry data). FIOGETNAME Gets the filename of the file descriptor. FIONREAD Gets the number of unread bytes in the file. FIOREADDIR Reads the next directory entry. FIOSEEK Sets the current byte offset in the file. FIOSYNC Flushes data to a remote NFS file. FIOWHERE Returns the current byte position in the file. 7.8.5 Non-NFS Network Devices VxWorks also supports network access to files on a remote host through the Remote Shell protocol (RSH) or the File Transfer Protocol (FTP). These implementations of network devices use the driver netDrv, which is included in the Wind River Network Stack. Using this driver, you can open, read, write, and close files located on remote systems without needing to manage the details of the underlying protocol used to effect the transfer of information. (For more information, see the Wind River Network Stack for VxWorks 6 Programmer’s Guide.) When a remote file is opened using RSH or FTP, the entire file is copied into local memory. As a result, the largest file that can be opened is restricted by the available memory. Read and write operations are performed on the memory-resident copy 400 7 I/O System 7.8 Devices in VxWorks of the file. When closed, the file is copied back to the original remote file if it was modified. In general, NFS devices are preferable to RSH and FTP devices for performance and flexibility, because NFS does not copy the entire file into local memory. However, NFS is not supported by all host systems. Creating Network Devices To access files on a remote host using either RSH or FTP, a network device must first be created by calling the routine netDevCreate( ). The arguments to netDevCreate( ) are (1) the name of the device, (2) the name of the host the device accesses, and (3) which protocol to use: 0 (RSH) or 1 (FTP). For example, the following call creates an RSH device called mars: that accesses the host mars. By convention, the name for a network device is the remote machine’s name followed by a colon (:). netDevCreate ("mars:", "mars", 0); Files on a network device can be created, opened, and manipulated as if on a local disk. Thus, opening the file mars:/usr/foo actually opens /usr/foo on host mars. Note that creating a network device allows access to any file or device on the remote system, while mounting an NFS file system allows access only to a specified file system. For the files of a remote host to be accessible with RSH or FTP, permissions and user identification must be established on both the remote and local systems. Creating and configuring network devices is discussed in detail in Wind River Network Stack for VxWorks 6 Programmer’s Guide: File Access Applications and in the API reference entry for netDrv. I/O Control Functions RSH and FTP devices respond to the same ioctl( ) functions as NFS devices except for FIOSYNC and FIOREADDIR. The functions are defined in the header file ioLib.h. For more information, see the API reference entries for netDrv and ioctl( ). 401 7 VxWorks Kernel Programmer's Guide, 6.6 7.8.6 Null Devices VxWorks provides both /null and /dev/null for null devices. The /null device is the traditional VxWorks null device, which is provided by default for backward compatibility. The /dev/null device is provided by the BUNDLE_RTP_POSIX_PSE52 component bundle, and is required for conformance with the POSIX PSE52 profile. Note that the devs shell command lists /null and /dev/null with other devices, but the ls command does not list /dev/null under the VRFS root directory (because the name violates the VRFS naming scheme). Applications can, in any case, use /null or /dev/null as required. For information about POSIX PSE52, see the VxWorks Kernel Programmer’s Guide: POSIX Facilities. For information about VRFS, see VxWorks Kernel Programmer’s Guide: Local File Systems. 7.8.7 Sockets In VxWorks, the underlying basis of network communications is sockets. A socket is an endpoint for communication between tasks; data is sent from one socket to another. Sockets are not created or opened using the standard I/O functions. Instead, they are created by calling socket( ), and connected and accessed using other routines in sockLib. However, after a stream socket (using TCP) is created and connected, it can be accessed as a standard I/O device, using read( ), write( ), ioctl( ), and close( ). The value returned by socket( ) as the socket handle is in fact an I/O system file descriptor. VxWorks socket routines are source-compatible with the BSD 4.4 UNIX socket functions and the Windows Sockets (Winsock 1.1) networking standard. Use of these routines is discussed in Wind River Network Stack for VxWorks 6 Programmer’s Guide. 7.8.8 Extended Block Device Facility: XBD The extended block device (XBD) facility mediates I/O activity between file systems and block devices. It provides a standard interface between file systems on the one hand, and block drivers on the other. The XBD facility also provides support for removable file systems, automatic file system detection, and multiple file systems. For more information on these features, see 8. Local File Systems. 402 7 I/O System 7.8 Devices in VxWorks NOTE: The XBD facility is required for some file systems (such as HRFS, dosFs, cdromFs, and rawFs), but not others (such as ROMFS). For detailed information on developing XBD-compatible device drivers, see the VxWorks Device Driver Developer’s Guide. The basic XBD facility is proved with the INCLUDE_XBD component, which also provides generic service for following optional components: INCLUDE_XBD_RAMDRV Provides support for RAM disks. See XBD RAM Disk, p.411. INCLUDE_XBD_PART_LIB Provides disk partitioning facilities. See XBD Disk Partition Manager, p.403. INCLUDE_XBD_BLK_DEV Provides support for legacy block device drivers that were designed to work with the predecessor to XBD—the cache block I/O (CBIO) facility. These devices include floppy drives, SCSI, and TrueFFS (the disk-access emulator for flash). See XBD Block Device Wrapper, p.404. INCLUDE_XBD_TRANS Provides a transaction-based file system (TRFS) facility, which can be used with dosFs. It provides fault-tolerant file system consistency and fast recovery in response to power loss. See 7.8.9 Transaction-Based Reliable File System Facility: TRFS, p.405. XBD Disk Partition Manager VxWorks provides support for PC-style disk partitioning with the INCLUDE_XBD_PART_LIB component, which facilitates sharing fixed disks and removable cartridges between VxWorks target systems and PCs running Windows. This component includes two modules: xbdPartition and partLib. xbdPartition Module The xbdPartition facility creates a device for each partition that is detected on media. Each partition that is detected is probed by the file system monitor and an I/O device is added to VxWorks. This device is an instantiation of the file system found by the file system monitor (or rawFs if the file system is not recognized or detected). If no partitions are detected, a single device is created to represent the entire media. There can be up to four partitions on a single media. For information about the file system monitor, see 8.2 File System Monitor, p.455. 403 7 VxWorks Kernel Programmer's Guide, 6.6 The partition facility also names the partitions. The names are derived from the base device name and the partition number. The base device name is derived from the device driver name (for more information in this regard, see the VxWorks Device Driver Developer’s Guide). For example, the XBD-compatible device for an ATA hard disk would have a base name of /ata00. If it had four partitions, they would be named as follows: /ata00:1 /ata00:2 /ata00:3 /ata00:4 If there were no partitions, the name would be /ata00:0. For an example of how the facility is used, see Example 8-1. partLib Library The partLib library provides facilities for creating PC-style partitions on media. It can create up to four primary partitions. Note that when partitions are created, any existing information on the media is lost. For more information see the VxWorks API reference for xbdCreatePartition( ). XBD Block Device Wrapper The INCLUDE_XBD_BLKDEV component provides support for legacy block devices that were designed to work the predecessor to XBD—the cache block I/O (CBIO) facility. It provides a wrapper XBD facility that converts the block I/O driver interface based on the BLK_DEV logical block device structure into an XBD API-compliant interface. NOTE: The Wind River devices that require the INCLUDE_XBD_BLKDEV component in addition to INCLUDE_XBD are floppy, SCSI, and TrueFFS (the disk-access emulator for flash) drivers. Any third-party device drivers based on the BLK_DEV interface also require INCLUDE_XBD_BLKDEV. The Wind River drivers that do not require the INCLUDE_XBD_BLK_DEV component are USB block storage, ATA, and the XBD RAM disk. ! CAUTION: Depending on the implementation of the driver, the INCLUDE_XBD_BLK_DEV component may not properly detect media insertion and removal. It may, therefore remove the file system when the media is removed, or not instantiate a file system when media is inserted. 404 7 I/O System 7.8 Devices in VxWorks XBD TRFS Component The INCLUDE_XBD_TRANS component is an XBD-compatible transaction-based reliable file system (TRFS) facility. TRFS an I/O facility that provides fault-tolerant file system layer for the dosFs file system. See 7.8.9 Transaction-Based Reliable File System Facility: TRFS, p.405 for more information. 7.8.9 Transaction-Based Reliable File System Facility: TRFS The transaction-based reliable file system (TRFS) facility provides a fault-tolerant file system I/O layer for the dosFs file system. It is provided with the INCLUDE_XBD_TRANS component. TRFS provides both file system consistency and fast recovery for the dosFs file system—DOS-compatible file systems are themselves neither reliable nor transaction-based. It is designed to operate with XBD-compliant device drivers for hard disks, floppy disks, compact flash media, TrueFFS flash devices, and so on. It can also be used with the XBD wrapper component for device drivers that are not XBD-compliant. TRFS provides reliability in resistance to sudden power loss: files and data that are already written to media are unaffected, they will not be deleted or corrupted because data is always written either in its entirety or not at all. TRFS provides additional guarantees in its transactional feature: data is always maintained intact up to a given commit transaction. User applications set transaction points on the file system. If there is an unexpected failure of the system, the file system is returned to the state it was in at the last transaction point. That is, if data has changed on the media after a commit transaction but prior to a power loss, it is automatically restored to the its state at the last commit transaction to further ensure data integrity. On mounting the file system, TRFS detects any failure and rolls back data to the last secure transaction. Unlike some facilities that provide data integrity on a file-by-file basis, TRFS protects the medium as a whole. It is transactional for a file system, which means that setting transaction points will commit all files, not just the one used to set the transaction point. 405 7 VxWorks Kernel Programmer's Guide, 6.6 NOTE: While TRFS is a I/O layer added to dosFs, it uses a modified on-media format that is not compatible with other FAT-based file systems, including Microsoft Windows and the VxWorks dosFs file system without the TRFS layer. It should not, therefore, be used when compatibility with other systems is a requirement For information about dosFs, see 8.5 MS-DOS-Compatible File System: dosFs, p.478. Configuring VxWorks With TRFS Configure VxWorks with the INCLUDE_XBD_TRANS component to provide TRFS functionality for your dosFs file system. Automatic Instantiation of TRFS TRFS is automatically detected and instantiated if the media has already been formatted for use with TRFS, in a manner very similar to the instantiation of the dosFs or HRFS file system. The primary difference is that when TRFS is detected by the file system monitor, it calls the TRFS creation function, and the creation function then creates another XBD instance and generates an insertion event for it. The monitor then detects the new XBD and begins probing. In this case, however, the monitor does not examine the media directly—all commands are routed through TRFS, which performs the appropriate translations. If a file system is detected, such as dosFs, the dosFs creation function is called by the monitor and dosFs is instantiated. If not, rawfs is instantiated. For information about how file systems are automatically instantiated, see 8.2 File System Monitor, p.455. Formatting a Device for TRFS TRFS low-level formatting is accomplished with the call: usrFormatTrans(device, overHead, type); The arguments are: device The volume name to format. For example, "/ata". 406 7 I/O System 7.8 Devices in VxWorks overHead An integer that identifies the portion of the disk to use as transactional workspace in parts-per-thousand of the disk. type An integer with the values of either FORMAT_REGULAR (0), which does not reserve any blocks from the disk; or FORMAT_TFFS (1), which reserves the first block. Once the TRFS format is complete, a dosFs file system can be created by calling the dosFs formatter on the same volume. When a FAT file system is created using the function dosFsVolFormat( ) in conjunction with TRFS, a transaction point is automatically inserted following the format. One cannot, therefore, unformat by rolling back a transaction point. Example 7-4 Formatting a Device for TRFS /* Create a RAM disk with 512 byte sized sectors and 1024 sectors.*/ if (xbdRamDiskDevCreate (512, 1024 * 512, 0, "/trfs") == NULL) { printf ("Could not create RAM disk\n"); return; } /* Put TRFS on the RAM disk */ if (usrFormatTrans ("/trfs", 100, 0) != OK) { printf ("Could not format\n"); return; } /* Now put dosFs on TRFS */ if (dosFsVolFormat ("/trfs", DOS_OPT_BLANK, 0) != OK) { printf ("Could not format for dos\n"); return; } /* Create a file on the TRFS/DosFS volume */ fd = open ("/trfs/myfile", O_CREAT | O_RDWR, 0666); if (fd < 0) { printf ("Couldn't create file\n"); return; } /* Commit the file creation to media */ ioctl (fd, CBIO_TRANS_COMMIT, 0); 407 7 VxWorks Kernel Programmer's Guide, 6.6 Using TRFS in Applications Once TRFS and dosFs are created, the dosFs file system may be used with the ordinary file creation and manipulation commands. No changes to the file system become permanent, however, until TRFS is used to commit them. It is important to note that the entire dosFs file system—and not individual files— are committed. The entire disk state must therefore be consistent before executing a commit; that is, there must not be a file system operation in progress (by another task, for example) when the file system is committed. If multiple tasks update the file system, care must be taken to ensure the file data is in a known state before setting a transaction point. There are two ways to commit the file system: ■ Using the volume name of the device formatted for TRFS. ■ Using a file descriptor which is open on TRFS. The function usrTransCommit( ) takes the volume name of the TRFS device and causes it to commit. The function usrTransCommitFd( ) takes a file descriptor open on TRFS and causes a commit of the entire file system. TRFS Code Examples The following code examples illustrate creating a file system with TRFS and setting a transaction point. The first routine creates a new TRFS layer and dosFs file system; and the second sets a transaction point. void createTrfs ( void ) { /* Create an XBD RAM disk with 512 byte sized sectors and 1024 sectors.*/ if (xbdRamDiskDevCreate (512, 1024 * 512, 0, "/trfs") == NULL) { printf ("Could not create XBD RAM disk\n"); return; } /* Put TRFS on the RAM disk */ /* Use 10% of the disk as overhead */ if (usrFormatTrans ("/trfs", 100, 0) != OK) { printf ("Could not format for TRFS\n"); return; } /* Now put dosFs on TRFS */ 408 7 I/O System 7.8 Devices in VxWorks if (dosFsVolFormat ("/trfs", DOS_OPT_BLANK, 0) != OK) { printf ("Could not format for dos\n"); return; } void transTrfs ( void ) { /* This assumes a TRFS with DosFs on "/trfs" */ 7 ... /* Perform file operations here */ usrTransCommit ("/trfs"); ... /* Perform more file operations here */ usrTransCommit ("/trfs"); } 409 VxWorks Kernel Programmer's Guide, 6.6 7.8.10 Block Devices A physical block device is a device that is organized as a sequence of individually accessible blocks of data. The most common type of block device is a disk. In VxWorks, the term block refers to the smallest addressable unit on the device. For most disk devices, a VxWorks block corresponds to a sector, although terminology varies. Block devices in VxWorks have a slightly different interface than other I/O devices. Rather than interacting directly with the I/O system, the I/O activity of block device drivers is mediated by the extended block device (XBD) facility and a file system. The XBD facility provides a standard interface for block device drivers on the one hand, and for file systems on the other. Figure 7-2 shows a layered model of I/O for both block and non-block (character) devices. This architecture allows the same block device driver to be used with different file systems, and reduces the number of I/O functions that must be supported in the driver. For information about the XBD facility, see 7.8.8 Extended Block Device Facility: XBD, p.402. For information about the file systems that can be used with block devices, see 8Local File Systems, p.451. For information about information about block device drivers and how to develop them, see the VxWorks Device Driver Developer’s Guide. 410 7 I/O System 7.8 Devices in VxWorks Figure 7-2 Non-Block Devices and Block Devices Application I/O System 7 driver table File System XBD Non-Block Device Driver Block Device Driver Device(s) Device(s) XBD RAM Disk A RAM driver emulates a disk device, but keeps all data in memory. The INCLUDE_XBD_RAMDRV component allows the use of a file system to access data 411 VxWorks Kernel Programmer's Guide, 6.6 stored in RAM memory. RAM disks can be created using volatile as well a non-volatile RAM. A RAM disk can be used with the HRFS, dosFs, and rawFs file systems. The RAM disk links into the file system monitor and event framework. For more about information about RAM disks, see the API reference for xbdRamDisk, as well as Example 7-4, Example 8-3, and Example 8-7. For information about compatible file systems, see 8.4 Highly Reliable File System: HRFS, p.459, 8.5 MS-DOS-Compatible File System: dosFs, p.478, and 8.6 Raw File System: rawFs, p.505. Note that the XBD-compatible RAM disk facility supersedes the ramDrv facility. SCSI Drivers SCSI is a standard peripheral interface that allows connection with a wide variety of hard disks, optical disks, floppy disks, tape drives, and CD-ROM devices. SCSI block drivers are compatible with the dosFs libraries, and offer several advantages for target configurations. They provide: ■ ■ local mass storage in non-networked environments faster I/O throughput than Ethernet networks The SCSI-2 support in VxWorks supersedes previous SCSI support, although it offers the option of configuring the original SCSI functionality, now known as SCSI-1. With SCSI-2 enabled, the VxWorks environment can still handle SCSI-1 applications, such as file systems created under SCSI-1. However, applications that directly used SCSI-1 data structures defined in scsiLib.h may require modifications and recompilation for SCSI-2 compatibility. The VxWorks SCSI implementation consists of two modules, one for the device-independent SCSI interface and one to support a specific SCSI controller. The scsiLib library provides routines that support the device-independent interface; device-specific libraries provide configuration routines that support specific controllers. There are also additional support routines for individual targets in sysLib.c. Configuring SCSI Drivers Components associated with SCSI drivers are listed in Table 7-14. 412 7 I/O System 7.8 Devices in VxWorks Table 7-14 SCSI and Related Components Component Description INCLUDE_SCSI Includes SCSI interface. INCLUDE_SCSI2 Includes SCSI-2 extensions. INCLUDE_SCSI_DMA Enables DMA for SCSI. INCLUDE_SCSI_BOOT Allows booting from a SCSI device. SCSI_AUTO_CONFIG Auto-configures and locates all targets on a SCSI bus. INCLUDE_DOSFS Includes the dosFs file system. INCLUDE_HRFS Includes the HRFS file system. INCLUDE_CDROMFS Includes CD-ROM file system support. 7 To include SCSI-1 functionality in VxWorks, use the INCLUDE_SCSI component. To include SCSI-2 functionality, you must use INCLUDE_SCSI2 in addition to INCLUDE_SCSI. Auto-configuration, DMA, and booting from a SCSI device are defined appropriately for each BSP. If you must change these settings, see the VxWorks API reference for sysScsiConfig( ) and the source file installDir/vxworks-6.x/target/src/config/usrScsi.c. ! CAUTION: Including SCSI-2 in your VxWorks image can significantly increase the image size. Configuring the SCSI Bus ID Each board in a SCSI-2 environment must define a unique SCSI bus ID for the SCSI initiator. SCSI-1 drivers, which support only a single initiator at a time, assume an initiator SCSI bus ID of 7. However, SCSI-2 supports multiple initiators, up to eight initiators and targets at one time. Therefore, to ensure a unique ID, choose a value in the range 0-7 to be passed as a parameter to the driver’s initialization routine (for example, ncr710CtrlInitScsi2( )) by the sysScsiInit( ) routine in sysScsi.c. For more information, see the reference entry for the relevant driver initialization routine. If there are multiple boards on one SCSI bus, and all of these boards use the same BSP, then different versions of the BSP must be compiled for each board by assigning unique SCSI bus IDs. 413 VxWorks Kernel Programmer's Guide, 6.6 ROM Size Adjustment for SCSI Boot If the INCLUDE_SCSI_BOOT component is included, larger ROMs may be required for some boards. Structure of the SCSI Subsystem The SCSI subsystem supports libraries and drivers for both SCSI-1 and SCSI-2. It consists of the following six libraries which are independent of any SCSI controller: scsiLib routines that provide the mechanism for switching SCSI requests to either the SCSI-1 library (scsi1Lib) or the SCSI-2 library (scsi2Lib), as configured by the board support package (BSP). scsi1Lib SCSI-1 library routines and interface, used when only INCLUDE_SCSI is used (see Configuring SCSI Drivers, p.412). scsi2Lib SCSI-2 library routines and all physical device creation and deletion routines. scsiCommonLib commands common to all types of SCSI devices. scsiDirectLib routines and commands for direct access devices (disks). scsiSeqLib routines and commands for sequential access block devices (tapes). Controller-independent support for the SCSI-2 functionality is divided into scsi2Lib, scsiCommonLib, scsiDirectLib, and scsiSeqLib. The interface to any of these SCSI-2 libraries can be accessed directly. However, scsiSeqLib is designed to be used in conjunction with tapeFs, while scsiDirectLib works with dosFs and rawFs. Applications written for SCSI-1 can be used with SCSI-2; however, SCSI-1 device drivers cannot. VxWorks targets using SCSI interface controllers require a controller-specific device driver. These device drivers work in conjunction with the controller-independent SCSI libraries, and they provide controller configuration and initialization routines contained in controller-specific libraries. For example, the Western Digital WD33C93 SCSI controller is supported by the device driver libraries wd33c93Lib, wd33c93Lib1, and wd33c93Lib2. Routines tied to SCSI-1 (such as wd33c93CtrlCreate( )) and SCSI-2 (such as wd33c93CtrlCreateScsi2( )) 414 7 I/O System 7.8 Devices in VxWorks are segregated into separate libraries to simplify configuration. There are also additional support routines for individual targets in sysLib.c. Booting and Initialization When VxWorks is built with the INCLUDE_SCSI component, the system startup code initializes the SCSI interface by executing sysScsiInit( ) and usrScsiConfig( ). The call to sysScsiInit( ) initializes the SCSI controller and sets up interrupt handling. The physical device configuration is specified in usrScsiConfig( ), which is in installDir/vxworks-6.x/target/src/config/usrScsi.c. The routine contains an example of the calling sequence to declare a hypothetical configuration, including: ■ definition of physical devices with scsiPhysDevCreate( ) ■ creation of logical partitions with scsiBlkDevCreate( ) ■ creation of an XBD block wrapper driver with xbdBlkDevCreate( ). If a recognized file system exists on the SCSI media, it is instantiated automatically when xbdBlkDevCreate( ) returns. If not, the file system formatter must be called to create the file system. See the dosFsVolFormat( ) API reference for information about creating a dosFs file system; see the hrfsFormat( ) API reference for creating an HRFS file system. If you are not using SCSI_AUTO_CONFIG, modify usrScsiConfig( ) to reflect your actual configuration. For more information on the calls used in this routine, see the reference entries for scsiPhysDevCreate( ), scsiBlkDevCreate( ), and xbdBlkDevCreate( ). Device-Specific Configuration Options The SCSI libraries have the following default behaviors enabled: ■ ■ ■ ■ ■ SCSI messages disconnects minimum period and maximum REQ/ACK offset tagged command queuing wide data transfer Device-specific options do not need to be set if the device shares this default behavior. However, if you must configure a device that diverges from these default characteristics, use scsiTargetOptionsSet( ) to modify option values. These options are fields in the SCSI_OPTIONS structure, shown below. SCSI_OPTIONS is declared in scsi2Lib.h. You can choose to set some or all of these option values to suit your particular SCSI device and application. 415 7 VxWorks Kernel Programmer's Guide, 6.6 typedef struct { UINT selTimeOut; BOOL messages; BOOL disconnect; UINT8 maxOffset; UINT8 minPeriod; SCSI_TAG_TYPE tagType; UINT maxTags; UINT8 xferWidth; } SCSI_OPTIONS; /* SCSI_OPTIONS - programmable options */ /* /* /* /* /* /* /* /* device selection time-out (us) FALSE => do not use SCSI messages FALSE => do not use disconnect max sync xfer offset (0 => async.) min sync xfer period (x 4 ns) default tag type max cmd tags available (0 => untag wide data trnsfr width in SCSI units */ */ */ */ */ */ */ */ There are numerous types of SCSI devices, each supporting its own mix of SCSI-2 features. To set device-specific options, define a SCSI_OPTIONS structure and assign the desired values to the structure’s fields. After setting the appropriate fields, call scsiTargetOptionsSet( ) to effect your selections. Example 7-6 illustrates one possible device configuration using SCSI_OPTIONS. Call scsiTargetOptionsSet( ) after initializing the SCSI subsystem, but before initializing the SCSI physical device. For more information about setting and implementing options, see the reference entry for scsiTargetOptionsSet( ). ! WARNING: Calling scsiTargetOptionsSet( ) after the physical device has been initialized may lead to undefined behavior. The SCSI subsystem performs each SCSI command request as a SCSI transaction. This requires the SCSI subsystem to select a device. Different SCSI devices require different amounts of time to respond to a selection; in some cases, the selTimeOut field may need to be altered from the default. If a device does not support SCSI messages, the boolean field messages can be set to FALSE. Similarly, if a device does not support disconnect/reconnect, the boolean field disconnect can be set to FALSE. The SCSI subsystem automatically tries to negotiate synchronous data transfer parameters. However, if a SCSI device does not support synchronous data transfer, set the maxOffset field to 0. By default, the SCSI subsystem tries to negotiate the maximum possible REQ/ACK offset and the minimum possible data transfer period supported by the SCSI controller on the VxWorks target. This is done to maximize the speed of transfers between two devices. However, speed depends upon electrical characteristics, like cable length, cable quality, and device termination; therefore, it may be necessary to reduce the values of maxOffset or minPeriod for fast transfers. 416 7 I/O System 7.8 Devices in VxWorks The tagType field defines the type of tagged command queuing desired, using one of the following macros: ■ ■ ■ ■ SCSI_TAG_UNTAGGED SCSI_TAG_SIMPLE SCSI_TAG_ORDERED SCSI_TAG_HEAD_OF_QUEUE For more information about the types of tagged command queuing available, see the ANSI X3T9-I/O Interface Specification Small Computer System Interface (SCSI-2). The maxTags field sets the maximum number of command tags available for a particular SCSI device. Wide data transfers with a SCSI target device are automatically negotiated upon initialization by the SCSI subsystem. Wide data transfer parameters are always negotiated before synchronous data transfer parameters, as specified by the SCSI ANSI specification, because a wide negotiation resets any prior negotiation of synchronous parameters. However, if a SCSI device does not support wide parameters and there are problems initializing that device, you must set the xferWidth field to 0. By default, the SCSI subsystem tries to negotiate the maximum possible transfer width supported by the SCSI controller on the VxWorks target in order to maximize the default transfer speed between the two devices. For more information on the actual routine call, see the reference entry for scsiTargetOptionsSet( ). SCSI Configuration Examples The following examples show some possible configurations for different SCSI devices. Example 7-5 is a simple block device configuration setup. Example 7-6 involves selecting special options and demonstrates the use of scsiTargetOptionsSet( ). Example 7-7 configures a SCSI device for synchronous data transfer. Example 7-8 shows how to configure the SCSI bus ID. These examples can be embedded either in the usrScsiConfig( ) routine or in a user-defined SCSI configuration function. Example 7-5 Configuring SCSI Drivers In the following example, usrScsiConfig( ) was modified to reflect a new system configuration. The new configuration has a SCSI disk with a bus ID of 4 and a Logical Unit Number (LUN) of 0 (zero). The disk is configured with a dosFs file system (with a total size of 0x20000 blocks) and a rawFs file system (spanning the remainder of the disk). 417 7 VxWorks Kernel Programmer's Guide, 6.6 The following usrScsiConfig( ) code reflects this modification. /* configure Winchester at busId = 4, LUN = 0 */ if ((pSpd40 = scsiPhysDevCreate (pSysScsiCtrl, 4, 0, 0, NONE, 0, 0, 0)) == (SCSI_PHYS_DEV *) NULL) { SCSI_DEBUG_MSG ("usrScsiConfig: scsiPhysDevCreate failed.\n"); } else { /* create block devices - one for dosFs and one for rawFs */ if (((pSbd0 = scsiBlkDevCreate (pSpd40, 0x20000, 0)) == NULL) || ((pSbd1 = scsiBlkDevCreate (pSpd40, 0, 0x20000)) == NULL)) { return (ERROR); } /* initialize both dosFs and rawFs file systems */ if ((xbdBlkDevCreate (pSbd0, "/sd0") == NULL) || (xbdBlkDevCreate (pSbd1,"/sd1") == NULL) { return (ERROR); } } If problems with your configuration occur, insert the following lines at the beginning of usrScsiConfig( ) to obtain further information on SCSI bus activity. #if FALSE scsiDebug = TRUE; scsiIntsDebug = TRUE; #endif Do not declare the global variables scsiDebug and scsiIntsDebug locally. They can be set or reset from the shell. 418 7 I/O System 7.8 Devices in VxWorks Example 7-6 Configuring a SCSI Disk Drive with Asynchronous Data Transfer and No Tagged Command Queuing In this example, a SCSI disk device is configured without support for synchronous data transfer and tagged command queuing. The scsiTargetOptionsSet( ) routine is used to turn off these features. The SCSI ID of this disk device is 2, and the LUN is 0: int SCSI_OPTIONS int which; option; devBusId; devBusId = 2; which = SCSI_SET_OPT_XFER_PARAMS | SCSI_SET_OPT_TAG_PARAMS; option.maxOffset = SCSI_SYNC_XFER_ASYNC_OFFSET; /* => 0 defined in scsi2Lib.h */ option.minPeriod = SCSI_SYNC_XFER_MIN_PERIOD; /* defined in scsi2Lib.h */ option.tagType = SCSI_TAG_UNTAGGED; /* defined in scsi2Lib.h */ option.maxTag = SCSI_MAX_TAGS; if (scsiTargetOptionsSet (pSysScsiCtrl, devBusId, &option, which) == ERROR) { SCSI_DEBUG_MSG ("usrScsiConfig: could not set options\n", 0, 0, 0, 0, 0, 0); return (ERROR); } /* configure SCSI disk drive at busId = devBusId, LUN = 0 */ if ((pSpd20 = scsiPhysDevCreate (pSysScsiCtrl, devBusId, 0, 0, NONE, 0, 0, 0)) == (SCSI_PHYS_DEV *) NULL) { SCSI_DEBUG_MSG ("usrScsiConfig: scsiPhysDevCreate failed.\n"); return (ERROR); } 419 7 VxWorks Kernel Programmer's Guide, 6.6 Example 7-7 Configuring a SCSI Disk for Synchronous Data Transfer with Non-Default Offset and Period Values In this example, a SCSI disk drive is configured with support for synchronous data transfer. The offset and period values are user-defined and differ from the driver default values. The chosen period is 25, defined in SCSI units of 4 ns. Thus, the period is actually 4 * 25 = 100 ns. The synchronous offset is chosen to be 2. Note that you may need to adjust the values depending on your hardware environment. int SCSI_OPTIONS int which; option; devBusId; devBusId = 2; which = SCSI_SET_IPT_XFER_PARAMS; option.maxOffset = 2; option.minPeriod = 25; if (scsiTargetOptionsSet (pSysScsiCtrl, devBusId &option, which) == ERROR) { SCSI_DEBUG_MSG ("usrScsiConfig: could not set options\n", 0, 0, 0, 0, 0, 0) return (ERROR); } /* configure SCSI disk drive at busId = devBusId, LUN = 0 */ if ((pSpd20 = scsiPhysDevCreate (pSysScsiCtrl, devBusId, 0, 0, NONE, 0, 0, 0)) == (SCSI_PHYS_DEV *) NULL) { SCSI_DEBUG_MSG ("usrScsiConfig: scsiPhysDevCreate failed.\n") return (ERROR); } Example 7-8 Changing the Bus ID of the SCSI Controller To change the bus ID of the SCSI controller, modify sysScsiInit( ) in sysScsi.c. Set the SCSI bus ID to a value between 0 and 7 in the call to xxxCtrlInitScsi2( ), where xxx is the controller name. The default bus ID for the SCSI controller is 7. Troubleshooting ■ Incompatibilities Between SCSI-1 and SCSI-2 Applications written for SCSI-1 may not execute for SCSI-2 because data structures in scsi2Lib.h, such as SCSI_TRANSACTION and SCSI_PHYS_DEV, have changed. This applies only if the application used these structures directly. 420 7 I/O System 7.8 Devices in VxWorks If this is the case, you can choose to configure only the SCSI-1 level of support, or you can modify your application according to the data structures in scsi2Lib.h. In order to set new fields in the modified structure, some applications may simply need to be recompiled, and some applications will have to be modified and then recompiled. ■ SCSI Bus Failure If your SCSI bus hangs, it could be for a variety of reasons. Some of the more common are: – Your cable has a defect. This is the most common cause of failure. – The cable exceeds the cumulative maximum length of 6 meters specified in the SCSI-2 standard, thus changing the electrical characteristics of the SCSI signals. – The bus is not terminated correctly. Consider providing termination power at both ends of the cable, as defined in the SCSI-2 ANSI specification. – The minimum transfer period is insufficient or the REQ/ACK offset is too great. Use scsiTargetOptionsSet( ) to set appropriate values for these options. – The driver is trying to negotiate wide data transfers on a device that does not support them. In rejecting wide transfers, the device-specific driver cannot handle this phase mismatch. Use scsiTargetOptionsSet( ) to set the appropriate value for the xferWidth field for that particular SCSI device. 421 7 VxWorks Kernel Programmer's Guide, 6.6 7.9 Differences Between VxWorks and Host System I/O Most commonplace uses of I/O in VxWorks are completely source-compatible with I/O in UNIX and Windows. However, note the following differences: ■ Device Configuration In VxWorks, device drivers can be installed and removed dynamically. But only in the kernel space. ■ File Descriptors In VxWorks, file descriptors are unique to the kernel and to each process—as in UNIX and Windows. The kernel and each process has its own universe of file descriptors, distinct from each other. When the process is created, its universe of file descriptors is initially populated by duplicating the file descriptors of its creator. (This applies only when the creator is a process. If the creator is a kernel task, only the three standard I/O descriptors 0, 1 and 2 are duplicated.) Thereafter, all open, close, or dup activities affect only that process’ universe of descriptors. In kernel and in each process, file descriptors are global to that entity, meaning that they are accessible by any task running in it. In the kernel, however, standard input, standard output, and standard error (0, 1, and 2) can be made task specific. For more information see 7.4.1 File Descriptors, p.365 and 7.4.3 Standard I/O Redirection, p.367. ■ I/O Control The specific parameters passed to ioctl( ) functions can differ between UNIX and VxWorks. ■ Driver Routines In UNIX, device drivers execute in system mode and cannot be preempted. In VxWorks, driver routines can be preempted because they execute within the context of the task that invoked them. 422 7 I/O System 7.10 Internal I/O System Structure 7.10 Internal I/O System Structure The VxWorks I/O system differs from most I/O systems in the way that the work of performing user I/O requests is distributed between the device-independent I/O system and the device drivers themselves. In many systems, the device driver supplies a few routines to perform low-level I/O functions such as reading a sequence of bytes from, or writing them to, character-oriented devices. The higher-level protocols, such as communications protocols on character-oriented devices, are implemented in the device-independent part of the I/O system. The user requests are heavily processed by the I/O system before the driver routines get control. While this approach is designed to make it easy to implement drivers and to ensure that devices behave as much alike as possible, it has several drawbacks. The driver writer is often seriously hampered in implementing alternative protocols that are not provided by the existing I/O system. In a real-time system, it is sometimes desirable to bypass the standard protocols altogether for certain devices where throughput is critical, or where the device does not fit the standard model. In the VxWorks I/O system, minimal processing is done on user I/O requests before control is given to the device driver. The VxWorks I/O system acts as a switch to route user requests to appropriate driver-supplied routines. Each driver can then process the raw user requests as appropriate to its devices. In addition, however, several high-level subroutine libraries are available to driver writers that implement standard protocols for both character- and block-oriented devices. Thus the VxWorks I/O system provides the best of both worlds: while it is easy to write a standard driver for most devices with only a few pages of device-specific code, driver writers are free to execute the user requests in nonstandard ways where appropriate. There are two fundamental types of device: block and character (or non-block; see Figure 7-2). Block devices are used for storing file systems. They are random access devices where data is transferred in blocks. Examples of block devices include hard and floppy disks. Character devices are typically of the tty/sio type. As discussed in earlier sections, the three main elements of the VxWorks I/O system are drivers, devices, and files. The following sections describe these elements in detail. The discussion focuses on character drivers; however, much of it is applicable to block devices. Because block drivers must interact with VxWorks file systems, they use a slightly different organization. 423 7 VxWorks Kernel Programmer's Guide, 6.6 NOTE: This discussion is designed to clarify the structure of VxWorks I/O facilities and to highlight some considerations relevant to writing I/O drivers for VxWorks. For detailed information about writing device drivers, see the VxWorks Device Driver Developer’s Guide. Example 7-9 shows the abbreviated code for a hypothetical driver that is used as an example throughout the following discussions. This example driver is typical of drivers for character-oriented devices. In VxWorks, each driver has a short, unique abbreviation, such as net or tty, which is used as a prefix for each of its routines. The abbreviation for the example driver is xx. Example 7-9 Hypothetical Driver /* * xxDrv - driver initialization routine * xxDrv() init’s the driver. It installs the driver via iosDrvInstall. * It may allocate data structures, connect ISRs, and initialize hardware */ STATUS xxDrv () { xxDrvNum = iosDrvInstall (xxCreat, 0, xxOpen, 0, xxRead, xxWrite, xxIoctl) ; (void) intConnect (intvec, xxInterrupt, ...); ... } /************************************************************************ * xxDevCreate - device creation routine * * Called to add a device called to be svced by this driver. Other * driver-dependent arguments may include buffer sizes, device addresses. * The routine adds the device to the I/O system by calling iosDevAdd. * It may also allocate and initialize data structures for the device, * initialize semaphores, initialize device hardware, and so on. */ STATUS xxDevCreate (name, ...) char * name; ... { status = iosDevAdd (xxDev, name, xxDrvNum); ... } 424 7 I/O System 7.10 Internal I/O System Structure /* * * The following routines implement the basic I/O functions. * The xxOpen() return value is meaningful only to this driver, * and is passed back as an argument to the other I/O routines. */ int xxOpen (xxDev, remainder, mode) XXDEV * xxDev; char * remainder; int mode; { /* serial devices should have no file name part */ 7 if (remainder[0] != 0) return (ERROR); else return ((int) xxDev); } int xxRead (xxDev, buffer, nBytes) XXDEV * xxDev; char * buffer; int nBytes; ... int xxWrite (xxDev, buffer, nBytes) ... int xxIoctl (xxDev, requestCode, arg) ... /* * * * * * * */ xxInterrupt - interrupt service routine Most drivers have routines that handle interrupts from the devices serviced by the driver. These routines are connected to the interrupts by calling intConnect (usually in xxDrv above). They can receive a single argument, specified in the call to intConnect (see intLib). VOID xxInterrupt (arg) ... 425 VxWorks Kernel Programmer's Guide, 6.6 7.10.1 Drivers A driver for a non-block device generally implements the seven basic I/O functions—creat( ), remove( ), open( ), close( ), read( ), write( ), and ioctl( )—for a particular kind of device. The driver implements these general functions with corresponding device-specific routines that are installed with iosDrvInstall( ). NOTE: Only VxBus-compatible drivers can be used with the symmetric multiprocessing (SMP) configuration of VxWorks. For general information about VxWorks SMP and about migration, see 15. VxWorks SMP and 15.15 Migrating Code to VxWorks SMP, p.702. Not all of the general I/O functions are implemented if they are not supported by a particular device. For example, remove( ) is usually not supported for devices that are not used with file systems. If any of the seven basic I/O routines are not implemented by a driver, a null function pointer should be used for the corresponding iosDrvInstall( ) parameter when the driver is installed. Any call to a routine that is not supported will then fail and return an ENOTSUP error. Drivers may (optionally) allow tasks to wait for activity on multiple file descriptors. This functionality is implemented with the driver’s ioctl( ) routine; see Implementing select( ), p.441. A driver for a block device interfaces with a file system, rather than directly with the I/O system. The file system in turn implements most I/O functions. The driver need only supply routines to read and write blocks, reset the device, perform I/O control, and check device status. When an application invokes one of the basic I/O functions, the I/O system routes the request to the appropriate routine of a specific driver, as described in the following sections. The driver’s routine runs in the calling task’s context, as though it were called directly from the application. Thus, the driver is free to use any facilities normally available to tasks, including I/O to other devices. This means that most drivers have to use some mechanism to provide mutual exclusion to critical regions of code. The usual mechanism is the semaphore facility provided in semLib. In addition to the routines that implement the seven basic I/O functions, drivers also have three other routines: ■ 426 An initialization routine that installs the driver in the I/O system, connects to any interrupts used by the devices serviced by the driver, and performs any necessary hardware initialization. This routine is typically named xxDrv( ). 7 I/O System 7.10 Internal I/O System Structure ■ A routine to add devices that are to be serviced by the driver to the I/O system. This routine is typically named xxDevCreate( ). ■ Interrupt-level routines that are connected to the interrupts of the devices serviced by the driver. The Driver Table and Installing Drivers The function of the I/O system is to route user I/O requests to the appropriate routine of the appropriate driver. The I/O system does this by maintaining a table that contains the address of each routine for each driver. Drivers are installed dynamically by calling the I/O system internal routine iosDrvInstall( ). The arguments to this routine are the addresses of the seven I/O routines for the new driver. The iosDrvInstall( ) routine enters these addresses in a free slot in the driver table and returns the index of this slot. This index is known as the driver number and is used subsequently to associate particular devices with the driver. Null (0) addresses can be specified for any of the seven basic I/O routines that are not supported by a device. For example, remove( ) is usually not supported for non-file-system devices, and a null is specified for the driver’s remove function. When a user I/O call matches a null driver routine, the call fails and an ENOTSUP error is returned. VxWorks file systems (such as dosFsLib) contain their own entries in the driver table, which are created when the file system library is initialized. 427 7 VxWorks Kernel Programmer's Guide, 6.6 Figure 7-3 Example – Driver Initialization for Non-Block Devices DRIVER CALL: drvnum = iosDrvInstall (xxCreat, 0, xxOpen, 0, xxRead, xxWrite, xxIoctl); [1] Driver’s install routine specifies driver routines for seven I/O functions. [2] I/O system locates next available slot in driver table. [4] I/O system returns driver number (drvnum = 2). create 0 1 2 xxCreat 3 4 DRIVER TABLE: 0 open close xxOpen 0 read write ioctl xxReadxxWrite xxIoctl delete [3] I/O system enters driver routines in driver table. Example of Installing a Driver Figure 7-3 shows the actions taken by the example driver and by the I/O system when the initialization routine xxDrv( ) runs. The driver calls iosDrvInstall( ), specifying the addresses of the driver’s routines for the seven basic I/O functions. Then, the I/O system: 1. Locates the next available slot in the driver table, in this case slot 2. 2. Enters the addresses of the driver routines in the driver table. 3. Returns the slot number as the driver number of the newly installed driver. 428 7 I/O System 7.10 Internal I/O System Structure 7.10.2 Devices Some drivers are capable of servicing many instances of a particular kind of device. For example, a single driver for a serial communications device can often handle many separate channels that differ only in a few parameters, such as device address. In the VxWorks I/O system, devices are defined by a data structure called a device header (DEV_HDR). This data structure contains the device name string and the driver number for the driver that services this device. The device headers for all the devices in the system are kept in a memory-resident linked list called the device list. The device header is the initial part of a larger structure determined by the individual drivers. This larger structure, called a device descriptor, contains additional device-specific data such as device addresses, buffers, and semaphores. The Device List and Adding Devices Non-block devices are added to the I/O system dynamically by calling the internal I/O routine iosDevAdd( ). The arguments to iosDevAdd( ) are the address of the device descriptor for the new device, the device’s name, and the driver number of the driver that services the device. The device descriptor specified by the driver can contain any necessary device-dependent information, as long as it begins with a device header. The driver does not need to fill in the device header, only the device-dependent information. The iosDevAdd( ) routine enters the specified device name and the driver number in the device header and adds it to the system device list. To add a block device to the I/O system, call the device initialization routine for the file system required on that device—for example, dosFsDevCreate( ). The device initialization routine then calls iosDevAdd( ) automatically. The routine iosDevFind( ) can be used to locate the device structure (by obtaining a pointer to the DEV_HDR, which is the first member of that structure) and to verify that a device name exists in the table. The following is an example using iosDevFind( ): 429 7 VxWorks Kernel Programmer's Guide, 6.6 char * pTail; /* pointer to tail of devName */ char devName[6] = "DEV1:"; /* name of device */ DOS_VOLUME_DESC * pDosVolDesc; /* first member is DEV_HDR */ ... pDosVolDesc = iosDevFind(devName, (char**)&pTail); if (NULL == pDosVolDesc) { /* ERROR: device name does not exist and no default device */ } else { /* * pDosVolDesc is a valid DEV_HDR pointer * and pTail points to beginning of devName. * Check devName against pTail to determine if it is * the default name or the specified devName. */ } Example of Adding Devices In Figure 7-4, the example driver’s device creation routine xxDevCreate( ) adds devices to the I/O system by calling iosDevAdd( ). 430 7 I/O System 7.10 Internal I/O System Structure Figure 7-4 Example – Addition of Devices to I/O System DRIVER CALLS: status = iosDevAdd (dev0, "/xx0", drvnum); status = iosDevAdd (dev1, "/xx1", drvnum); I/O system adds device descriptors to device list. Each descriptor contains device name and driver number (in this case 2) and any device-specific data. 7 DEVICE LIST: "/dk0/" 1 DRIVER TABLE: "/xx0" 2 "/xx1" 2 devicedependent data devicedependent data create delete open close read write ioctl 0 1 2 3 4 Deleting Devices A device can be deleted with iosDevDelete( ) and the associated driver removed with iosDrvRemove( ). Note that a device-deletion operation causes the file descriptors that are open on the device to be invalidated, but not closed. The file descriptors can only be closed by an explicit act on the part of an application. If this were not the case, and file descriptors were closed automatically by the I/O system, the descriptors could be reassigned to new files while they were still being used by an application that was unaware of the deletion of the device. The new files could then be accessed unintentionally by an application attempting to use the files associated with the 431 VxWorks Kernel Programmer's Guide, 6.6 deleted device, as well as by an application that was correctly using the new files. This would result in I/O errors and possible device data corruption. Because the file descriptors of a device that has been deleted are invalid, any subsequent I/O calls that use them—except close( )—will fail. The behavior of the I/O routines in this regard is as follows: ■ close( ) releases the file descriptor at I/O system level and the driver close routine is not called. ■ read( ), write( ), and ioctl( ) fail with error ENXIO (no such device or address). ■ While open( ), remove( ), and create( ) do not take an open file descriptor as input, they fail because the device name is no longer in the device list. Note that even if a device is deleted and immediately added again with the same device name, the file descriptors that were invalidated with the deletion are not restored to valid status. The behavior of the I/O calls on the associated file descriptors is the same as if the device had not been added again. Applications that are likely to encounter device deletion should be sure to check for ENXIO errors from read( ), write( ), and ioctl( ) calls, and to then close the relevant file descriptors. Using Callback Routines to Manage Device Deletion For situations in which devices are dynamically installed and deleted, the iosDevDelCallback( ) routine provides the means for calling a post-deletion handler after all driver invocations are exited. A common use of a device deletion callback is to prevent a race condition that would result from a device descriptor being deleted in one thread of execution while it was still being used in another. A device descriptor belongs to an application, and the I/O system cannot control its creation and release. It is a user data structure with DEV_HDR data structure embedded at the front of it, followed by any specific member of the device. Its pointer can be used to pass into any iosDevXyz( ) routine as a DEV_HDR pointer, or used as the device descriptor for user device handling. When a device is deleted, an application should not immediately release the device descriptor memory after iosDevDelete( ) and iosDrvRemove( ) calls because a driver invocation of the deleted device might still be in process. If the device descriptor is deleted while it is still in use by a driver routine, serious errors could occur. 432 7 I/O System 7.10 Internal I/O System Structure For example, the following would produce a race condition: task A invokes the driver routine xyzOpen( ) by a call to open( ) and the xyzOpen( ) call does not return before task B deletes the device and releases the device descriptor. However, if descriptor release is not performed by task B, but by a callback function installed with iosDevDelCallback( ), then the release occurs only after task A’s invocation of the driver routine has finished. A device callback routine is called immediately when a device is deleted with iosDevDelete( ) or iosDrvRemove( ) as long as no invocations of the associated driver are operative (that is, the device driver reference counter is zero). Otherwise, the callback routine is not executed until the last driver call exits (and the device driver reference counter reaches zero). A device deletion callback routine should be called with only one parameter, the pointer to the DEV_HDR data structure of the device in question. For example: devDeleteCallback(pDevHdr) The callback should be installed with iosDevDelCallback( ) after the iosDevAdd( ) call. The following code fragments illustrate callback use. The file system device descriptor pVolDesc is installed into the I/O device list. Its device deletion callback, fsVolDescRelease( ) performs the post-deletion processing, including releasing memory allocated for the device volume descriptor. void fsVolDescRelease ( FS_VOLUME_DESC * pVolDesc ) { . . . . . . free (pVolDesc->pFsemList); free (pVolDesc->pFhdlList); free (pVolDesc->pFdList); . . . . . . } STATUS fsDevCreate ( char * pDevName, /* device name */ device_t device, /* underlying block device */ u_int maxFiles, /* max no. of simultaneously open files */ u_int devCreateOptions /* write option & volume integrity */ ) { FS_VOLUME_DESC *pVolDesc = NULL; /* volume descriptor ptr */ . . . . . . pVolDesc = (FS_VOLUME_DESC *) malloc (sizeof (*pVolDesc)); pVolDesc->device = device; 433 7 VxWorks Kernel Programmer's Guide, 6.6 . . . . . . if (iosDevAdd((void *)pVolDesc, pDevName, fsDrvNum ) == ERROR) { pVolDesc->magic = NONE; goto error_iosadd; } /* Device deletion callback installed to release memory resource. */ iosDevDelCallback((DEV_HDR *) pVolDesc, (FUNCPTR) fsVolDescRelease); . . . . . . } STATUS fsDevDelete ( FS_VOLUME_DESC *pVolDesc /* pointer to volume descriptor */ ) { . . . . . . /* * Delete the file system device from I/O device list. Callback * fsVolDescRelease will be called from now on at a * safe time by I/O system. */ iosDevDelete((DEV_HDR *) pVolDesc); . . . . . . } The application should check the error returned by a deleted device, as follows: if (write (fd, (char *)buffer, nbytes) == ERROR) { if (errno == ENXIO) { /* Device is deleted. fd must be closed by application. */ close(fd); } else { /* write failure due to other reason. Do some error dealing. */ . . . . . . } } 434 7 I/O System 7.10 Internal I/O System Structure 7.10.3 File Descriptors Several file descriptors can be open to a single device at one time. A device driver can maintain additional information associated with a file descriptor beyond the I/O system’s device information. In particular, devices on which multiple files can be open at one time have file-specific information (for example, file offset) associated with each file descriptor. You can also have several file descriptors open to a non-block device, such as a tty; typically there is no additional information, and thus writing on any of the file descriptors produces identical results. 7 File Descriptor Table Files are opened with open( ) or creat( ). The I/O system searches the device list for a device name that matches the filename (or an initial substring) specified by the caller. If a match is found, the I/O system uses the driver number contained in the corresponding device header to locate and call the driver’s open routine in the driver table. The I/O system must establish an association between the file descriptor used by the caller in subsequent I/O calls, and the driver that services it. Additionally, the driver must associate some data structure per descriptor. In the case of non-block devices, this is usually the device descriptor that was located by the I/O system. The I/O system maintains these associations in a table called the file descriptor table. This table contains the driver number and an additional driver-determined 4-byte value. The driver value is the internal descriptor returned by the driver’s open routine, and can be any value the driver requires to identify the file. In subsequent calls to the driver’s other I/O functions (read( ), write( ), ioctl( ), and close( )), this value is supplied to the driver in place of the file descriptor in the application-level I/O call. 435 VxWorks Kernel Programmer's Guide, 6.6 Example of Opening a File In Figure 7-5 and Figure 7-6, a user calls open( ) to open the file /xx0. The I/O system takes the following series of actions: 1. It searches the device list for a device name that matches the specified filename (or an initial substring). In this case, a complete device name matches. 2. It reserves a slot in the file descriptor table and creates a new file descriptor object, which is used if the open is successful. 3. It then looks up the address of the driver’s open routine, xxOpen( ), and calls that routine. Note that the arguments to xxOpen( ) are transformed by the I/O system from the user’s original arguments to open( ). The first argument to xxOpen( ) is a pointer to the device descriptor the I/O system located in the full filename search. The next parameter is the remainder of the filename specified by the user, after removing the initial substring that matched the device name. In this case, because the device name matched the entire filename, the remainder passed to the driver is a null string. The driver is free to interpret this remainder in any way it wants. In the case of block devices, this remainder is the name of a file on the device. In the case of non-block devices like this one, it is usually an error for the remainder to be anything but the null string. The third parameter is the file access flag, in this case O_RDONLY; that is, the file is opened for reading only. The last parameter is the mode, as passed to the original open( ) routine. 4. It executes xxOpen( ), which returns a value that subsequently identifies the newly opened file. In this case, the value is the pointer to the device descriptor. This value is supplied to the driver in subsequent I/O calls that refer to the file being opened. Note that if the driver returns only the device descriptor, the driver cannot distinguish multiple files opened to the same device. In the case of non-block device drivers, this is usually appropriate. 5. The I/O system then enters the driver number and the value returned by xxOpen( ) in the new file descriptor object. Again, the value entered in the file descriptor object has meaning only for the driver, and is arbitrary as far as the I/O system is concerned. 6. 436 Finally, it returns to the user the index of the slot in the file descriptor table, in this case 3. 7 I/O System 7.10 Internal I/O System Structure Figure 7-5 Example: Call to I/O Routine open( ) [Part 1] USER CALL: DRIVER CALL: fd = open ("/xx0", O_RDONLY, 0); xxdev = xxOpen (xxdev, "", O_RDONLY, 0); [1] I/O system finds name in device list. [2] I/O system reserves [3] I/O system calls driver’s open routine a slot in the file descriptor with pointer to table. device descriptor. pDevHdr value FILE DESCRIPTOR TABLE: 0 1 2 3 4 DEVICE LIST: "/dk0/" 1 "/xx0" 2 "/xx1" 2 devicedependent data DRIVER TABLE: create delete 0 1 2 3 4 open close read write ioctl xxOpen 437 7 VxWorks Kernel Programmer's Guide, 6.6 Figure 7-6 Example: Call to I/O Routine open( ) [Part 2] USER CALL: DRIVER CALL: fd = open ("/xx0", O_RDONLY, 0); xxdev = xxOpen (xxdev, "", O_RDONLY, 0); [6] I/O system returns index in table of new open file (fd = 3). [5] I/O system enters driver number and identifying value in reserved table slot. FILE DESCRIPTOR TABLE: [4] Driver returns any identifying value, in this case the pointer to the device descriptor. drvnum value 0 1 2 3 4 2 xxdev DEVICE LIST: "/dk0/" 1 "/xx0" 2 "/xx1" 2 devicedependent data create delete DRIVER TABLE: 0 1 2 3 4 438 open close read write ioctl 7 I/O System 7.10 Internal I/O System Structure Example of Reading Data from the File In Figure 7-7, the user calls read( ) to obtain input data from the file. The specified file descriptor is the index into the file descriptor table for this file. The I/O system uses the driver number contained in the table to locate the driver’s read routine, xxRead( ). The I/O system calls xxRead( ), passing it the identifying value in the file descriptor table that was returned by the driver’s open routine, xxOpen( ). Again, in this case the value is the pointer to the device descriptor. The driver’s read routine then does whatever is necessary to read data from the device. The process for user calls to write( ) and ioctl( ) follow the same procedure. 439 7 VxWorks Kernel Programmer's Guide, 6.6 Figure 7-7 Example: Call to I/O Routine read( ) USER CALL: DRIVER CALL: n = read (fd, buf, len); n = xxRead (xxdev, buf, len); I/O system transforms the user’s I/O routine calls into driver routine calls replacing the fd with the value returned by the driver’s open routine, xxOpen( ). drvnum value FILE DESCRIPTOR TABLE: 0 1 2 3 4 2 xxdev DEVICE LIST: "/dk0/" 1 "/xx0" 2 "/xx1" 2 devicedependent data DRIVER TABLE: 440 create remove open 0 1 2 3 4 close read xxRead write ioctl 7 I/O System 7.10 Internal I/O System Structure Example of Closing a File The user terminates the use of a file by calling close( ). As in the case of read( ), the I/O system uses the driver number contained in the file descriptor table to locate the driver’s close routine. In the example driver, no close routine is specified; thus no driver routines are called. Instead, the I/O system marks the slot in the file descriptor table as being available. Any subsequent references to that file descriptor cause an error. Subsequent calls to open( ) can reuse that slot. 7 Implementing select( ) Supporting select( ) in your driver allows tasks to wait for input from multiple devices or to specify a maximum time to wait for the device to become ready for I/O. Writing a driver that supports select( ) is simple, because most of the functionality is provided in selectLib. You might want your driver to support select( ) if any of the following is appropriate for the device: ■ The tasks want to specify a timeout to wait for I/O from the device. For example, a task might want to time out on a UDP socket if the packet never arrives. ■ The driver supports multiple devices, and the tasks want to wait simultaneously for any number of them. For example, multiple pipes might be used for different data priorities. ■ The tasks want to wait for I/O from the device while also waiting for I/O from another device. For example, a server task might use both pipes and sockets. To implement select( ), the driver must keep a list of tasks waiting for device activity. When the device becomes ready, the driver unblocks all the tasks waiting on the device. For a device driver to support select( ), it must declare a SEL_WAKEUP_LIST structure (typically declared as part of the device descriptor structure) and initialize it by calling selWakeupListInit( ). This is done in the driver’s xxDevCreate( ) routine. When a task calls select( ), selectLib calls the driver’s ioctl( ) routine with the function FIOSELECT or FIOUNSELECT. If ioctl( ) is called with FIOSELECT, the driver must do the following: 441 VxWorks Kernel Programmer's Guide, 6.6 1. Add the SEL_WAKEUP_NODE (provided as the third argument of ioctl( )) to the SEL_WAKEUP_LIST by calling selNodeAdd( ). 2. Use the routine selWakeupType( ) to check whether the task is waiting for data to read from the device (SELREAD) or if the device is ready to be written (SELWRITE). 3. If the device is ready (for reading or writing as determined by selWakeupType( )), the driver calls the routine selWakeup( ) to make sure that the select( ) call in the task does not pend. This avoids the situation where the task is blocked but the device is ready. If ioctl( ) is called with FIOUNSELECT, the driver calls selNodeDelete( ) to remove the provided SEL_WAKEUP_NODE from the wakeup list. When the device becomes available, selWakeupAll( ) is used to unblock all the tasks waiting on this device. Although this typically occurs in the driver’s ISR, it can also occur elsewhere. For example, a pipe driver might call selWakeupAll( ) from its xxRead( ) routine to unblock all the tasks waiting to write, now that there is room in the pipe to store the data. Similarly the pipe’s xxWrite( ) routine might call selWakeupAll( ) to unblock all the tasks waiting to read, now that there is data in the pipe. 442 7 I/O System 7.10 Internal I/O System Structure Example 7-10 Driver Code Using the Select Facility /* This code fragment shows how a driver might support select(). In this * example, the driver unblocks tasks waiting for the device to become ready * in its interrupt service routine. */ /* myDrvLib.h - header file for driver */ typedef struct /* MY_DEV */ { DEV_HDR devHdr; BOOL myDrvDataAvailable; BOOL myDrvRdyForWriting; SEL_WAKEUP_LIST selWakeupList; } MY_DEV; /* /* /* /* device header */ data is available to read */ device is ready to write */ list of tasks pended in select */ /* myDrv.c - code fragments for supporting select() in a driver */ #include #include /* First create and initialize the device */ STATUS myDrvDevCreate ( char * name, ) { MY_DEV * pMyDrvDev; ... additional driver code ... /* name of device to create */ /* pointer to device descriptor*/ /* allocate memory for MY_DEV */ pMyDrvDev = (MY_DEV *) malloc (sizeof MY_DEV); ... additional driver code ... /* initialize MY_DEV */ pMyDrvDev->myDrvDataAvailable=FALSE pMyDrvDev->myDrvRdyForWriting=FALSE /* initialize wakeup list */ selWakeupListInit (&pMyDrvDev->selWakeupList); ... additional driver code ... } /* ioctl function to request reading or writing */ STATUS myDrvIoctl ( MY_DEV * pMyDrvDev, /* pointer to device descriptor */ 443 7 VxWorks Kernel Programmer's Guide, 6.6 int request, int arg ) { ... additional driver code ... /* ioctl function */ /* where to send answer */ switch (request) { ... additional driver code ... case FIOSELECT: /* add node to wakeup list */ selNodeAdd (&pMyDrvDev->selWakeupList, (SEL_WAKEUP_NODE *) arg); if (selWakeupType ((SEL_WAKEUP_NODE *) arg) == SELREAD && pMyDrvDev->myDrvDataAvailable) { /* data available, make sure task does not pend */ selWakeup ((SEL_WAKEUP_NODE *) arg); } if (selWakeupType ((SEL_WAKEUP_NODE *) arg) == SELWRITE && pMyDrvDev->myDrvRdyForWriting) { /* device ready for writing, make sure task does not pend */ selWakeup ((SEL_WAKEUP_NODE *) arg); } break; case FIOUNSELECT: /* delete node from wakeup list */ selNodeDelete (&pMyDrvDev->selWakeupList, (SEL_WAKEUP_NODE *) arg); break; ... additional driver code ... } } /* code that actually uses the select() function to read or write */ void myDrvIsr ( MY_DEV * pMyDrvDev; ) { ... additional driver code ... /* if there is data available to read, wake up all pending tasks */ if (pMyDrvDev->myDrvDataAvailable) selWakeupAll (&pMyDrvDev->selWakeupList, SELREAD); 444 7 I/O System 7.10 Internal I/O System Structure /* if the device is ready to write, wake up all pending tasks */ if (pMyDrvDev->myDrvRdyForWriting) selWakeupAll (&pMyDrvDev->selWakeupList, SELWRITE); } Cache Coherency NOTE: The cache facilities described in this section are provided for the uniprocessor (UP) configuration of VxWorks, some of which are not appropriate— and not provided—for the symmetric multiprocessor (SMP) configuration. For more information in this regard, see cacheLib Restrictions, p.708. For general information about VxWorks SMP and about migration, see 15. VxWorks SMP and 15.15 Migrating Code to VxWorks SMP, p.702. Drivers written for boards with caches must guarantee cache coherency. Cache coherency means data in the cache must be in sync, or coherent, with data in RAM. The data cache and RAM can get out of sync any time there is asynchronous access to RAM (for example, DMA device access or VMEbus access). Data caches are used to increase performance by reducing the number of memory accesses. Figure 7-8 shows the relationships between the CPU, data cache, RAM, and a DMA device. Data caches can operate in one of two modes: writethrough and copyback. Write-through mode writes data to both the cache and RAM; this guarantees cache coherency on output but not input. Copyback mode writes the data only to the cache; this makes cache coherency an issue for both input and output of data. Figure 7-8 Cache Coherency CPU Data Cache RAM DMA Device 445 7 VxWorks Kernel Programmer's Guide, 6.6 If a CPU writes data to RAM that is destined for a DMA device, the data can first be written to the data cache. When the DMA device transfers the data from RAM, there is no guarantee that the data in RAM was updated with the data in the cache. Thus, the data output to the device may not be the most recent—the new data may still be sitting in the cache. This data incoherence can be solved by making sure the data cache is flushed to RAM before the data is transferred to the DMA device. If a CPU reads data from RAM that originated from a DMA device, the data read can be from the cache buffer (if the cache buffer for this data is not marked invalid) and not the data just transferred from the device to RAM. The solution to this data incoherence is to make sure that the cache buffer is marked invalid so that the data is read from RAM and not from the cache. Drivers can solve the cache coherency problem either by allocating cache-safe buffers (buffers that are marked non-cacheable) or flushing and invalidating cache entries any time the data is written to or read from the device. Allocating cache-safe buffers is useful for static buffers; however, this typically requires MMU support. Non-cacheable buffers that are allocated and freed frequently (dynamic buffers) can result in large amounts of memory being marked non-cacheable. An alternative to using non-cacheable buffers is to flush and invalidate cache entries manually; this allows dynamic buffers to be kept coherent. The routines cacheFlush( ) and cacheInvalidate( ) are used to manually flush and invalidate cache buffers. Before a device reads the data, flush the data from the cache to RAM using cacheFlush( ) to ensure the device reads current data. After the device has written the data into RAM, invalidate the cache entry with cacheInvalidate( ). This guarantees that when the data is read by the CPU, the cache is updated with the new data in RAM. 446 7 I/O System 7.10 Internal I/O System Structure Example 7-11 DMA Transfer Routine /* This a sample DMA transfer routine. Before programming the device * to output the data to the device, it flushes the cache by calling * cacheFlush(). On a read, after the device has transferred the data, * the cache entry must be invalidated using cacheInvalidate(). */ #include #include #include #include "example.h" void exampleDmaTransfer /* 1 = READ, 0 = WRITE */ ( UINT8 *pExampleBuf, int exampleBufLen, int xferDirection ) { if (xferDirection == 1) { myDevToBuf (pExampleBuf); cacheInvalidate (DATA_CACHE, pExampleBuf, exampleBufLen); } else { cacheFlush (DATA_CACHE, pExampleBuf, exampleBufLen); myBufToDev (pExampleBuf); } } 447 7 VxWorks Kernel Programmer's Guide, 6.6 It is possible to make a driver more efficient by combining cache-safe buffer allocation and cache-entry flushing or invalidation. The idea is to flush or invalidate a cache entry only when absolutely necessary. To address issues of cache coherency for static buffers, use cacheDmaMalloc( ). This routine initializes a CACHE_FUNCS structure (defined in cacheLib.h) to point to flush and invalidate routines that can be used to keep the cache coherent. The macros CACHE_DMA_FLUSH and CACHE_DMA_INVALIDATE use this structure to optimize the calling of the flush and invalidate routines. If the corresponding function pointer in the CACHE_FUNCS structure is NULL, no unnecessary flush/invalidate routines are called because it is assumed that the buffer is cache coherent (hence it is not necessary to flush/invalidate the cache entry manually). The driver code uses a virtual address and the device uses a physical address. Whenever a device is given an address, it must be a physical address. Whenever the driver accesses the memory, it must use the virtual address. The device driver should use CACHE_DMA_VIRT_TO_PHYS to translate a virtual address to a physical address before passing it to the device. It may also use CACHE_DMA_PHYS_TO_VIRT to translate a physical address to a virtual one, but this process is time-consuming and non-deterministic, and should be avoided whenever possible. 448 7 I/O System 7.10 Internal I/O System Structure Example 7-12 Address-Translation Driver /* The following code is an example of a driver that performs address * translations. It attempts to allocate a cache-safe buffer, fill it, and * then write it out to the device. It uses CACHE_DMA_FLUSH to make sure * the data is current. The driver then reads in new data and uses * CACHE_DMA_INVALIDATE to guarantee cache coherency. */ #include #include #include "myExample.h" STATUS myDmaExample (void) { void * pMyBuf; void * pPhysAddr; 7 /* allocate cache safe buffers if possible */ if ((pMyBuf = cacheDmaMalloc (MY_BUF_SIZE)) == NULL) return (ERROR); … fill buffer with useful information … /* flush cache entry before data is written to device */ CACHE_DMA_FLUSH (pMyBuf, MY_BUF_SIZE); /* convert virtual address to physical */ pPhysAddr = CACHE_DMA_VIRT_TO_PHYS (pMyBuf); /* program device to read data from RAM */ myBufToDev (pPhysAddr); … wait for DMA to complete … … ready to read new data … /* program device to write data to RAM */ myDevToBuf (pPhysAddr); … wait for transfer to complete … /* convert physical to virtual address */ pMyBuf = CACHE_DMA_PHYS_TO_VIRT (pPhysAddr); /* invalidate buffer */ CACHE_DMA_INVALIDATE (pMyBuf, MY_BUF_SIZE); … use data … /* when done free memory */ if (cacheDmaFree (pMyBuf) == ERROR) return (ERROR); return (OK); } 449 VxWorks Kernel Programmer's Guide, 6.6 7.11 PCMCIA A PCMCIA card can be plugged into notebook computers to connect devices such as modems and external hard drives.2 VxWorks provides PCMCIA facilities for pcPentium, pcPentium2, and pcPentium3 BSPs and PCMCIA drivers that allow VxWorks running on these targets to support PCMCIA hardware. PCMCIA support is at the PCMCIA Release 2.1 level. It does not include socket services or card services, which are not required by VxWorks. It does include chip drivers and libraries. The PCMCIA libraries and drivers are also available in source code form for VxWorks systems based on CPU architectures other than Intel Pentium. To include PCMCIA support in your system, configure VxWorks with the INCLUDE_PCMCIA component. For information about PCMCIA facilities, see the API references for pcmciaLib and pcmciaShow. 7.12 Peripheral Component Interconnect: PCI Peripheral Component Interconnect (PCI) is a bus standard for connecting peripherals to a PC, and is used in Pentium systems, among others. PCI includes buffers that de-couple the CPU from relatively slow peripherals, allowing them to operate asynchronously. For information about PCI facilities, see the API references for pciAutoConfigLib, pciConfigLib, pciInitLib, and pciConfigShow. 2. PCMCIA stands for Personal Computer Memory Card International Association, and refers to both the association and the standards that it has developed. 450 8 Local File Systems 8.1 Introduction 452 8.2 File System Monitor 455 8.3 Virtual Root File System: VRFS 457 8.4 Highly Reliable File System: HRFS 459 8.5 MS-DOS-Compatible File System: dosFs 478 8.6 Raw File System: rawFs 505 8.7 CD-ROM File System: cdromFs 510 8.8 Read-Only Memory File System: ROMFS 516 8.9 Target Server File System: TSFS 518 451 VxWorks Kernel Programmer's Guide, 6.6 8.1 Introduction VxWorks provides a variety of file systems that are suitable for different types of applications. The file systems can be used simultaneously, and in most cases in multiple instances, for a single VxWorks system. Most VxWorks file systems rely on the extended block device (XBD) facility for a a standard I/O interface between the file system and device drivers. This standard interface allows you to write your own file system for VxWorks, and freely mix file systems and device drivers. File systems used for removable devices make use of the file system monitor for automatic detection of device insertion and instantiation of the appropriate file system on the device. The relationship between applications, file systems, I/O facilities, device drivers and hardware devices is illustrated in Figure 8-1. Note that this illustration is relevant for the HRFS, dosFs, rawFs, and cdromFs file systems. The dotted line indicates the elements that must be configured and instantiated to create a specific, functional run-time file system. 452 8 Local File Systems 8.1 Introduction Figure 8-1 File Systems in a VxWorks System Application I/O System 8 File System HRFS, dosFs, rawFs, cdromFs XBD Facility Block Device SCSI, ATA, RAM disk, Floppy, TrueFFS, and so on Hardware For information about the XBD facility, see 7.8.8 Extended Block Device Facility: XBD, p.402. 453 VxWorks Kernel Programmer's Guide, 6.6 This chapter discusses the file system monitor and the following VxWorks file systems, describing how they are organized, configured, and used: ■ VRFS A virtual root file system for use with applications that require a POSIX root file system. The VRFS is simply a root directory from which other file systems and devices can be accessed. See 8.3 Virtual Root File System: VRFS, p.457. ■ HRFS A POSIX-compliant transactional file system designed for real-time use of block devices (disks). Can be used on flash memory in conjunction with TrueFFS and the XBD block wrapper component. See 8.4 Highly Reliable File System: HRFS, p.459. ■ dosFs An MS-DOS compatible file system designed for real-time use of block devices. Can be used with flash memory in conjunction with the TrueFFS and the XBD block wrapper component. Can also be used with the transaction-based reliable file system (TRFS) facility. See 8.5 MS-DOS-Compatible File System: dosFs, p.478. ■ rawFS Provides a simple raw file system that treats an entire disk as a single large file. See 8.6 Raw File System: rawFs, p.505. ■ cdromFs Allows applications to read data from CD-ROMs formatted according to the ISO 9660 standard file system. See 8.7 CD-ROM File System: cdromFs, p.510. ■ ROMFS Designed for bundling applications and other files with a VxWorks system image. No storage media is required beyond that used for the VxWorks boot image. See 8.8 Read-Only Memory File System: ROMFS, p.516. ■ TSFS Uses the host target server to provide the target with access to files on the host system. See 8.9 Target Server File System: TSFS, p.518. For information about the XBD facility, see 7.8.8 Extended Block Device Facility: XBD, p.402). 454 8 Local File Systems 8.2 File System Monitor File Systems and Flash Memory VxWorks can be configured with file-system support for flash memory devices using TrueFFS and the HRFS or dosFs file system. For more information, see 8.5 MS-DOS-Compatible File System: dosFs, p.478 and 10. Flash File System Support: TrueFFS. NOTE: This chapter provides information about facilities available in the VxWorks kernel. For information about facilities available to real-time processes, see the VxWorks Application Programmer’s Guide: Local File Systems. 8 8.2 File System Monitor The file system monitor provides for automatic detection of device insertion, and instantiation of the appropriate file system on the device. The monitor is required for all file systems that are used with the extended block device (XBD) facility. It is provided with the INCLUDE_FS_MONITOR component. The file systems that require both the XBD and the file system monitor components are HRFS, dosFs, rawFs, and cdromFs. The process by which devices are detected, and file systems created, is as follows: 1. When file systems are initialized (at boot time), they register probe routines and instantiation routines with the file system monitor. 2. When a device is detected or inserted (for example, when a driver is initialized, or media is inserted into an existing device—such as a floppy disk into a floppy drive) the block device associated with it generates a primary insertion event. (See Device Insertion Events, p.456.) 3. In response to the primary insertion event, the file system monitor creates an XBD partition manager if the device can support partitions. (For information about the partition manager, see XBD Disk Partition Manager, p.403.) 4. If the partition manager finds partitions on the physical device, it creates a device for each partition; and whether or not partitions are found, the manager generates a secondary insertion event. 5. When the file system monitor receives a secondary event, all the registered file system probe functions are run. 455 VxWorks Kernel Programmer's Guide, 6.6 6. When a file system's probe routine returns success, that file system's instantiation routine is executed. If none of the probes are successful, or if the file system instantiation routine fails, a rawFs file system is created on the device by default. When a device is removed, the following occurs: 1. The block device detects the removal of the hardware device associated with it and generates a removal event. 2. The block device removes itself, freeing all its resources. 3. The file system associated with the block device removes itself from core I/O, invalidating its file handles. 4. The file system removes itself, freeing all its resources. Device Insertion Events The types of device insertion events to which the file system monitor responds are described in more detail below. XBD Primary Insertion Event An XBD-compliant block device generates a primary insertion event when media that can support partitions is inserted (that is, if a partition table is found). In response, the file system monitor creates a partition manager, which in turn generates secondary insertion events for each partition that it finds on the media (see below). Note that for block devices used with the XBD wrapper component (INCLUDE_XBD_BLK_DEV), a primary insertion event is always generated, regardless of the media. The wrapper element is essentially hardware agnostic; it cannot know if the device might include partitions. For example, the device could be a hard disk—for which partitions are expected—or it could be a floppy device. Note also that a RAM disk device can generate a primary insertion event, depending on the parameters used when it was created (see XBD RAM Disk, p.411 and the API reference for XbdRamDisk). XBD Secondary Insertion Event A secondary insertion event is generated by either by a block device whose media does not support partitions, or by an XBD partition manager. The secondary event signals the file system manager to run the probe routines that identify the file system on the device. If a probe routine returns OK, the 456 8 Local File Systems 8.3 Virtual Root File System: VRFS associated file system creation routine is executed. If none of the probe routines identifies a file system, or if a file system creation routine fails, the rawFs file system is created by default. XBD Soft Insert Event Unlike the other events, an XBD soft insert event is produced by application directive rather than by physical media being swapped. When ioctl( ) is called with the XBD_SOFT_EJECT control function it tells the file system manager that the current file system has been removed, and that a rawFs file system should be created. This call causes the system to bypass the usual file system detection operations, and ensures that rawFs is instantiated in place of the current file system. XBD Name Mapping Facility The file system monitor name mapping facility allows XBD names to be mapped to a more suitable name. It's primary use is for the partition manager which appends :x to the base xbd name when it detects a partition. By using the fsm name facility you can map the partition names to something more useful. For example, the floppy drive configlette uses the name component to map the supplied floppy name plus the :0 the partition manager will add to /fdx. Where x represents the floppy drive number. If this was not done one would see the default device names in the list generated by the devs shell command. For more information see the API references for fsmNameInstall( ), fsmNameMap( ), and fsmNameUninstall( ); also see Example 8-2. 8.3 Virtual Root File System: VRFS VxWorks provides a virtual root file system (VRFS) for use with applications that require a POSIX root file system. The VRFS is simply a “/” or root directory from which other file systems and devices can be accessed. VRFS is not a true file system, as files and directories cannot be created with the sorts of commands that are ordinarily associated with file systems, and it is read-only. Only devices whose names begin with a single leading forward slash—and which do not contain any other forward slash characters—are recognized by the VRFS. 457 8 VxWorks Kernel Programmer's Guide, 6.6 To include the VRFS in VxWorks, configure the kernel with the INCLUDE_VRFS component. The VRFS is created and mounted automatically if the component is included in VxWorks. This shell session illustrates the relationship between device names and access to devices and file systems with the VRFS. -> devs drv name 0 /null 1 /tyCo/0 1 /tyCo/1 2 /aioPipe/0x1817040 6 /romfs 7 / 9 yow-build02-lx: 10 /vio 11 /shm 12 /ram0 value = 25 = 0x19 -> cd "/" value = 0 = -> ll ?--------drwxrwxr-x ?--------drwxrwxrwx drwxrwxrwx value = 0 = 0x0 0 0 0 15179 0 0 1 0 1 0 0x0 0 100 0 0 0 0 20 0 0 2048 Jan 1 00:00 null Jan 23 2098 romfs/ Jan 1 00:00 vio Jan 1 00:00 shm/ Jan 1 00:00 ram0/ Note that /tyCo/0, /tyCo/1, /aioPipe/0x1817040 and yow-build02-lx do not show up in the directory listing of the root directory as they do not follow the naming convention required by the VRFS. The first three include forward slashes in the body of the device name and the fourth does not have a leading forward slash in its name. Also note that the listings of file systems have a trailing forward slash character. Other devices do not, and they have a question mark in the permissions (or attributes) column of the listing because they do not have recognizable file permissions. NOTE: Configuring VxWorks with support for POSIX PSE52 conformance (using BUNDLE_RTP_POSIX_PSE52) provides the /dev/null device. Note that the devs shell command lists /dev/null with other devices, but the ls command does not list /dev/null under the VRFS root directory (because the name violates the VRFS naming scheme). Applications can, in any case, use /dev/null as required. For information about null devices, see 7.8.6 Null Devices, p.402. For information about POSIX PSE52, see the VxWorks Application Programmer’s Guide: POSIX Facilities. 458 8 Local File Systems 8.4 Highly Reliable File System: HRFS ! CAUTION: VRFS alters the behavior of other file systems because it provides a root directory on VxWorks. Changing directory to an absolute path on a host file system will not work when VRFS is installed without preceding the absolute path with the VxWorks device name. For example, if the current working directory is hostname, changing directory to /home/panloki will not work— it must be named hostname:/home/panloki. 8 8.4 Highly Reliable File System: HRFS The Highly Reliable File System (HRFS) is a transactional file system for real-time systems. The primary features of the file system are: ■ Fault tolerance. The file system is never in an inconsistent state, and is therefore able to recover quickly from unexpected loses of power. ■ Configurable commit policies. ■ Hierarchical file and directory system, allowing for efficient organization of files on a volume. ■ Compatibility with a widely available storage devices. ■ POSIX compliance. For more information about the HRFS libraries see the VxWorks API references for hrfsFormatLib, hrFsLib, and hrfsChkDskLib. HRFS and Flash Memory For information about using HRFS with flash memory, see 10. Flash File System Support: TrueFFS. 8.4.1 Configuring VxWorks for HRFS To include HRFS support in VxWorks, configure the kernel with the appropriate required and optional components. 459 VxWorks Kernel Programmer's Guide, 6.6 Required Components The components required for HRFS are the following: ■ Either the INCLUDE_HRFS or the INCLUDE_HRFS_READONLY component is required. As its name indicates, the latter is a read-only version of the main HRFS component. The libraries it provides are smaller as it provides no facilities for disk modifications. ■ The appropriate component for your block device; for example, INCLUDE_ATA. ■ If you are using a device driver that is not designed for use with the XBD facility, you must use the INCLUDE_XBD_BLK_DEV wrapper component in addition to INCLUDE_XBD. See XBD Block Device Wrapper, p.404 for more information. Optional HRFS Components The INCLUDE_HRFS_FORMAT (formatter), INCLUDE_HRFS_CHKDSK (consistency checker), and INCLUDE_HRFS_ACCESS_TIMESTAMP (access file stamp) components are optional. Note that the INCLUDE_HRFS_ACCESS_TIMESTAMP component is included in the BUNDLE_RTP_POSIX_PSE52 component bundle. Optional XBD Components The INCLUDE_XBD_PART_LIB (disk partitioning) and INCLUDE_XBD_RAMDRV (RAM disk) components are optional. For information about the XBD facility, see 7.8.8 Extended Block Device Facility: XBD, p.402). 8.4.2 Configuring HRFS HRFS provides the following component configuration parameters: HRFS_DEFAULT_MAX_BUFFERS Defines how many buffers HRFS uses for its caching mechanism. HRFS needs a minimum of 6 buffers. The default setting is 16. This parameter applies to all HRFS volumes. Note that while increasing the number of buffers can increase performance, it does so at the expense of heap memory. 460 8 Local File Systems 8.4 Highly Reliable File System: HRFS HRFS_DEFAULT_MAX_FILES Defines how many files can be simultaneously open on an HRFS volume. The minimum is 1. The default setting is 10. Note that is not the same as the maximum number of file descriptors. HRFS_DEFAULT_COMMIT_POLICY Defines the default commit policy for an HRFS volume, which is FS_COMMIT_AUTO. Commit policies can also be changed at runtime. For more information see 8.4.5 Transactional Operations and Commit Policies, p.469 and 8.4.6 Configuring Transaction Points at Runtime, p.471. HRFS_DEFAULT_COMMIT_PERIOD Defines the initial commit period of an HRFS volume if it has been configured for periodic commits. This parameter is measured in milliseconds. The default value is 5000 milliseconds (5 seconds). The commit period can also be changed at runtime. For more information see 8.4.5 Transactional Operations and Commit Policies, p.469 and 8.4.6 Configuring Transaction Points at Runtime, p.471. 8.4.3 Creating an HRFS File System This section describes the process of creating an HRFS file system. It first provides a summary overview and then a detailed description of each step. See 8.4.4 HRFS, ATA, and RAM Disk Examples, p.463 for examples of the steps and code examples. Overview of HRFS File System Creation For information operating system configuration, see 8.4.1 Configuring VxWorks for HRFS, p.459. Note that the file system is initialized automatically at boot time. The steps involved in creating an HRFS file system are as follows: 1. If you are using a custom driver, create the appropriate block device. See Step 1:Create a Block Device, p.462. If you are using a standard VxWorks component for the device, it is created automatically. 2. If you are using a device driver that is not XBD-compliant, create an XBD device wrapper. See Step 2:Create an XBD Device Wrapper, p.462 (Also see XBD Block Device Wrapper, p.404.). 3. Optionally, create and mount partitions. See Step 3:Create Partitions, p.463. 461 8 VxWorks Kernel Programmer's Guide, 6.6 4. If you are not using pre-formatted disks, format the volumes. See Step 4:Formatting the Volume, p.463. HRFS File System Creation Steps Before any other operations can be performed, the HRFS file system library, hrFsLib, must be initialized. This happens automatically at boot time, triggered by the required HRFS components that were included in the system. Initializing HRFS involves the creation of a vnode layer. HRFS installs an number of internal vnode operators into the this layer. The vnode layer invokes iosDrvInstall( ) when media is detected, which adds the driver to the I/O driver table. The driver number assigned to vnodes—and therefore HRFS—is recorded in a global variable, vnodeAffDriverNumber. The table specifies entry points for the vnode file operations that are accessing devices using HRFS. Step 1: Create a Block Device If you are using a standard VxWorks component for the device, it is created automatically. If you are using a custom driver, create the appropriate block device by calling the creation routine for the device driver. The format for this routine is xxxDevCreate( ) where xxx represents the device driver type; for example, ataDevCreate( ). The driver routine returns a pointer to a block device descriptor structure, BLK_DEV. This structure describes the physical attributes of the device and specifies the routines that the device driver provides. The pointer returned is used to create an XBD device wrapper in the next step. Step 2: Create an XBD Device Wrapper If you are using a device driver that is not XBD-compliant, it requires an XBD device wrapper. The wrapper is created automatically if you have configured VxWorks with the INCLUDE_XBD_BLK_DEV wrapper component (See XBD Block Device Wrapper, p.404). Otherwise, create a wrapper for each block device using xbdBlkDevCreate( ). After the XBD device wrapper is created, the physical device is automatically probed for a file system and partitions. If a disk is already formatted, the disk is 462 8 Local File Systems 8.4 Highly Reliable File System: HRFS mounted. If a file system is found, it is mounted as well. If file system is not HRFS, it must be formatted (see below). Step 3: Create Partitions If you have included the INCLUDE_XBD_PART_LIB component in your system, you can create partitions on a disk and mount volumes atop the partitions. Use the xbdCreatePartition( ) routine to create partitions. This step should only be performed once, when the disk is first initialized. If partitions are already written to the disk, this step should not be performed as it destroys data. 8 Step 4: Formatting the Volume If you are using unformatted disk or wish to replace the current file system on the disk, format the disk by calling hrFsFormat( ). For more information, see the VxWorks API reference for this routine. ! CAUTION: Reformatting a disk destroys any data that may be on it. 8.4.4 HRFS, ATA, and RAM Disk Examples This section provides examples of the steps discussed in the preceding section. They are meant to be relatively generic, and illustrate the following: ! ■ Creating and working with an HRFS file system on an ATA disk with commands from the shell. ■ Code that creates and formats partitions. ■ Code that creates and formats a RAM disk volume. CAUTION: Because device names are recognized by the I/O system using simple substring matching, file systems should not use a slash (/) alone as a name; unexpected results may otherwise occur. Example 8-1 Create HRFS in Partitions on an ATA Disk This example demonstrates how to initialize an ATA disk with HRFS on two partitions from the shell. While these steps use an ATA device, they are applicable to other block devices. 463 VxWorks Kernel Programmer's Guide, 6.6 1. If you are using a custom driver, create an ATA block device that controls the master ATA hard disk (drive zero) on the primary ATA controller (controller zero). This device uses the entire disk. -> xbd = ataXbdDevCreate(0,0,0,0,"/ata") New symbol "xbd" added to kernel symbol table. Instantiating /ata:0 as rawFs xbd = 0xca4fe0: value = 262145 = 0x40001 The xbd variable is of type device_t. A value of zero would indicate an error in the ataXbdDevCreate( ) call, which usually indicates a BSP configuration or hardware configuration error. If you are using the standard INCLUDE_ATA device component, the block device is created automatically. Note that in this case the default device name (provided by the component) is /ata0a. 2. Display information about devices. -> devs drv name 0 /null 1 /tyCo/0 1 /tyCo/1 8 yow-grand: 9 /vio 4 /ata:0 value = 25 = 0x19 3. The new ata driver /ata:0 is listed. The zero in the name indicates that no partitions were detected. Note that if no file system is detected on the device, the rawFs file system is instantiated automatically and appears in the device list. Prepare the disk for first use. Create two partitions on this disk device, specifying 50% of the disk space for the second partition, leaving 50% for the first partition. This step should only be performed once, when the disk is first initialized. If partitions are already written to the disk, this step should not be performed since it destroys any data on the disk. -> xbdCreatePartition ("/ata:0", 2, 50, 0, 0) value = 0 = 0x0 The four arguments are to xbdCreatePartition( ) are: ■ ■ ■ ■ ■ the drive name the number of partitions the percent of disk to use for the second partition the percent of disk to use for the third partition the percent of disk to use for the fourth partition The remainder of the disk is used for the first partition. 464 8 Local File Systems 8.4 Highly Reliable File System: HRFS 4. Then list the devices to display information about the new partitions. -> devs drv name 0 /null 1 /tyCo/0 1 /tyCo/1 8 yow-grand: 9 /vio 3 /ata:1 3 /ata:2 Note that /ata:0 does not appear in this list, and two new devices, /ata:1 and /ata:2, have been added to represent the new partitions. Each volume has rawfs instantiated in it as they are new and unformatted. 5. Format the volumes for HRFS. This step need only be done once, when the volumes are first created. If the volumes have already been formatted, then omit this step. This example formats the file system volumes with default options. -> hrfsFormat ("/ata:1", 0ll, 0, 0) Formatting /ata:1 for HRFS Instantiating /ata:1 as rawFs Formatting...OK. value = 0 = 0x0 -> hrfsFormat ("/ata:2", 0ll, 0, 0) Formatting /ata:2 for HRFS Instantiating /ata:2 as rawFs Formatting...OK. value = 0 = 0x0 Note that in the hrfsFormat( ) call, the ll (two lower-case L letters) used with the second parameter is required to indicate to the shell that the data type is long long. For more information, see the API reference for hrFsFormatLib. 6. Display information about the HRFS volumes. -> ll "/ata:1" Listing Directory /ata:1: drwxrwxrwx 1 0 0 drwxrwxrwx 1 0 0 value = 0 = 0x0 8192 Jan 8192 Jan 1 00:13 ./ 1 00:13 ../ 8192 Jan 8192 Jan 1 00:13 ./ 1 00:13 ../ -> ll "/ata:2" Listing Directory /ata:2: drwxrwxrwx 1 0 0 drwxrwxrwx 1 0 0 value = 0 = 0x0 465 8 VxWorks Kernel Programmer's Guide, 6.6 If you are working with an ATA hard disk or a CD-ROM file system from an ATAPI CD-ROM drive, you can, alternatively, use usrAtaConfig( ). This routine processes several steps at once. For more information, see the API reference. Example 8-2 Creating and Partitioning a Disk and Creating Volumes This code takes the name of a block device that you have already instantiated, creates three partitions, creates the partition handler for these partitions, and creates the HRFS device handler for them. Then it formats the partitions using hrfsFormat( ). STATUS usrPartDiskFsInit ( char * xbdName /* device name used during creation of XBD */ ) { const char * devNames[] = { "/sd0a", "/sd0b", "/sd0c" }; devname_t xbdPartName; int i; /* Map partition names */ for (i = 1; i <= 3; i++) { sprintf (xbdPartName, "%s:d", devNames[i],i); fsmNameInstall (devNames[i-1], xbdPartName); } /* create partitions */ if((xbdCreatePartition (xbdName,3,50,45)) == ERROR) return ERROR; /* Formatting the first partition */ if(hrfsFormat (devNames[0], 0ll,0, 0) == ERROR) return ERROR; /* Formatting the second partition */ if(hrfsFormat (devNames[1], 0ll, 0, 0) == ERROR) return ERROR; /* Formatting the third partition */ if(hrfsFormat (devNames[2], 0ll, 0, 0) == ERROR) return ERROR; return OK; } 466 8 Local File Systems 8.4 Highly Reliable File System: HRFS Note that in most cases you would be likely to format the different partitions for different file systems. Example 8-3 Creating and Formatting a RAM Disk Volume and Performing File I/O The following code creates a RAM disk, formats it for use with the HRFS file system, and performs file system operations. #include #include #include #include #include #include #include #define #define #define DEVNAME "/myram" /* name of the RAM disk */ BLOCKSIZE 512 DISKSIZE (BLOCKSIZE * 2000) 8 STATUS hrfsSetup ( void ) { STATUS error; device_t xbd; /* Create a RAM disk. Don’t support partitions */ xbd = xbdRamDiskDevCreate (BLOCKSIZE, DISKSIZE, 0, DEVNAME); if (xbd == NULLDEV) { printf("Failed to create RAM disk. errno = 0x%x\n", errno); return (ERROR); } /* * Format the RAM disk for HRFS. Allow for upto a 1000 files/directories * and let HRFS determine the logical block size. */ error = hrfsFormat (DEVNAME, 0ll, 0, 1000); if (error != OK) { printf("Failed to format RAM disk. errno = 0x%x\n", errno); return (ERROR); } printf ("%s now ready for use.\n", DEVNAME); return (OK); } 467 VxWorks Kernel Programmer's Guide, 6.6 STATUS hrfsFileExample ( void ) { int fd; char path[PATH_MAX]; char *testString = "hello world"; int size = strlen (testString) + 1; /* size of test string including EOS */ int len; /* Create a file under the root directory */ /* First build the path */ sprintf (path, "%s/myfile", DEVNAME); fd = open (path, O_RDWR | O_CREAT, 0777); if (fd < 0) { printf ("Couldn’t create file %s. errno = 0x%x\n", path, errno); return (ERROR); } /* Write to the file */ printf("Writing %d bytes to file.\n", size); len = write (fd, testString, size); if (len != size) { printf ("Couldn’t write to file %s. errno = 0x%x\n", path, errno); close (fd); return (ERROR); } /* Close and re-open file */ close (fd); fd = open (path, O_RDWR, 0777); if (fd < 0) { printf ("Couldn’t re-open file %s. errno = 0x%x\n", path, errno); return (ERROR); } /* Now read back what we wrote */ printf("Reading %d bytes from file.\n", size); len = read (fd, path, size); if (len != 12) { printf ("Couldn’t read from file %s. errno = 0x%x\n", path, errno); close (fd); return (ERROR); } 468 8 Local File Systems 8.4 Highly Reliable File System: HRFS /* Make sure we read what we wrote */ if ((len = strcmp (path, testString)) != 0) { printf ("Read data different from written data. errno = 0x%x, %d\n", errno, len); close (fd); return (ERROR); } close (fd); return (OK); } Note that to use this code, you must configure VxWorks with the INCLUDE_HRFS_FORMAT, INCLUDE_XBD_RAMDRV and INCLUDE_XBD_PART_LIB components. 8 The following illustrates running the example from the shell. -> hrfsSetup Instantiating /myram as rawFs Formatting /myram for HRFS Instantiating /myram as rawFs Formatting...OK. /myram now ready for use. value = 0 = 0x0 -> hrfsFileExample Writing 12 bytes to file. Reading 12 bytes from file. value = 0 = 0x0 -> ll "/myram" Listing Directory /myram: drwxrwxrwx 1 0 0 drwxrwxrwx 1 0 0 -rwxrwxrwx 1 0 0 value = 0 = 0x0 -> 2048 Jan 2048 Jan 12 Jan 1 00:00 ./ 1 00:00 ../ 1 00:00 myfile 8.4.5 Transactional Operations and Commit Policies HRFS is a transactional file system. That is, transaction or commit points are set to make disk changes permanent. Commit points can be configured to be set under different conditions, which are referred to as policies. Some disk operations trigger commits regardless of the policy. Under certain circumstances, HRFS rollbacks undo disk changes since the last commit, in order to protect the integrity of the file system. For information about static and dynamic configuration of commit policies, see 8.4.2 Configuring HRFS, p.460 and 8.4.6 Configuring Transaction Points at Runtime, p.471. 469 VxWorks Kernel Programmer's Guide, 6.6 Commit Policies The HRFS commit policies are as follows: Automatic Any operation that changes data on the disk results in a transaction point being set. This is the safest policy in terms of the potential for data loss. It is also the slowest in terms of performance, as every write to disk cause a commit. This is the default policy. There is no need for explicit action on the part of an application to commit a change. The following routines, for example, cause modifications to disk and result in a commit when the automatic policy is in force: ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ write( ) remove( ) delete( ) mkdir( ) rmdir( ) link( ) unlink( ) truncate( ) ftruncate( ) ioctl( ) when used with a control function that requires modifying the disk. Manual The application decides when a commit is to be performed. The user explicitly sets transaction points. This is the fastest policy in terms of performance but obviously has the potential for greater data loss. The application can, however, decide when critical data has been written and needs to be committed. The commit( ) routine is used with this policy. Periodic Transaction points are set automatically at periodic intervals. This policy is in between automatic and manual in terms of performance and potential data loss. 470 8 Local File Systems 8.4 Highly Reliable File System: HRFS Mandatory Commits For both manual and periodic commit policies there are circumstances under which a commit is always performed. Mandatory commits occur under the following circumstances: ■ Creation of a file or directory ■ Deletion of a file or directory. ■ Renaming/moving a file or directory. ■ Space in the inode journal is exhausted. ■ Commit policy is changed at runtime. 8 Note that mandatory commits are a subset of automatic commits—they do not, for example, include write( ) and truncate( ). Rollback A rollback undoes any disk changes since the last commit. Rollbacks usually occur when the system is unexpectedly powered down or reset. Rollbacks can also occur when the file system encounters errors; for example, the lack of disk space to complete a write( ), or an error is reported by the underlying device driver. Rollbacks of this nature only happen on operations that modify the media. Errors on read operations do not force a rollback. A rollback involves HRFS returning to the state of the disk at the last transaction point, which thereby preserves the integrity of the file system, but at the expense of losing file data that has changed since the last transaction point. If the manual or periodic commit policy is specified, there is the potential for losing a lot of data—although the integrity of the file system is preserved. 8.4.6 Configuring Transaction Points at Runtime The Highly Reliable File System (HRFS) provides configurable transaction points, which allow for finer control of how and when transaction points are set. The HRFS_DEFAULT_COMMIT_POLICY and HRFS_DEFAULT_COMMIT_PERIOD component configuration parameters are used to statically define the default commit policy and period (for more information see 8.4.2 Configuring HRFS, p.460). 471 VxWorks Kernel Programmer's Guide, 6.6 Both kernel and RTP applications can change commit policies at runtime. The following ioctl( ) functions are used to get and set commit policies: ■ ■ ■ ■ FIOCOMMITPOLICYGETFS FIOCOMMITPOLICYSETFS FIOCOMMITPERIODGETFS FIOCOMMITPERIODSETFS The commit policy for each volume can be changed using the ioctl( ) function FIOCOMMITPOLICYSETFS as the second parameter. The third parameter then specifies the actual commit policy: FS_COMMIT_POLICY_AUTO, FS_COMMIT_POLICY_MANUAL, or FS_COMMIT_POLICY_PERIODIC. If an HRFS volume has been configured for periodic commits, the commit period can be changed with ioctl( ) function FIOCOMMITPERIODSETFS. The third parameter is used to specify the commit period in milliseconds. If 0 is specified then the default commit period is used. The commit( ) routine can be used to commit programmatically. The routine is provided by the INCLUDE_DISK_UTILS component. Example 8-4 Setting an HRFS Commit Policy at Runtime /* open root directory of an HRFS volume */ fd = open ("/hrfs", O_READONLY, 0666); if (fd < 0) return ERROR; /* Set commit policy to manual */ if (ioctl (fd, FIOCOMMITPOLICYSETFS, (void *)FS_COMMIT_POLICY_MANUAL)) == ERROR) return ERROR; /* Policy set to manual. Change policy to periodic */ if (ioctl (fd, FIOCOMMITPOLICYSETFS, (void *)FS_COMMIT_POLICY_PERIODIC)) == ERROR) return ERROR; /* Policy set to periodic. Change commit period to 10 seconds*/ if (ioctl (fd, FIOCOMMITPERIODSETFS, (void *)10000)) == ERROR) return ERROR; /* Period set to 10 seconds. Change commit period back to default */ if (ioctl (fd, FIOCOMMITPERIODSETFS, (void *)0)) == ERROR) return ERROR; /* Period reset. Change policy back to automatic */ if (ioctl (fd, FIOCOMMITPOLICYSETFS, (void *)FS_COMMIT_POLICY_AUTO)) == ERROR) return ERROR; 472 8 Local File Systems 8.4 Highly Reliable File System: HRFS 8.4.7 File Access Time Stamps Access time stamps can be enabled by configuring VxWorks with the INCLUDE_HRFS_ACCESS_TIMESTAMP component. The component is include in the BUNDLE_RTP_POSIX_PSE52 component bundle. For access time stamps to be saved to disk, the volume must be formatted with HRFS on-disk format 1.2 or greater. Version 1.2 is the default version for VxWorks 6.3. See API references for hrfsAdvFormat( ) and hrfsAdvFormatFd( ) for more information. When the access timestamp component is included, and the appropriate disk format version is used, reading from a file or directory causes its access time stamp to be updated. This can cause significant performance loss, as a write to disk occurs even on a read operation and a transaction point is set. Only use access time stamps if the application requires it for POSIX compliance. 8.4.8 Maximum Number of Files and Directories HRFS files and directories are stored on disk in data structures called inodes. During formatting the maximum number of inodes is specified as a parameter to hrfsFormat( ). The total number of files and directories can never exceed the number inodes. Attempting to create a file or directory when all inodes are in use generates an error. Deleting a file or directory frees the corresponding inode. 8.4.9 Working with Directories This section discusses creating and removing directories, and reading directory entries. Creating Subdirectories You can create as many subdirectories as there are inodes. Subdirectories can be created in the following ways: ■ With open( ). To create a directory, the O_CREAT option must be set in the flags parameter and the S_IFDIR or FSTAT_DIR option must be set in the mode parameter. The open( ) calls returns a file descriptor that describes the new directory. The file descriptor can only be used for reading only and should be closed when it no longer needed. 473 8 VxWorks Kernel Programmer's Guide, 6.6 ■ With mkdir( ) from usrFsLib. When creating a directory using either of the above methods, the new directory name must be specified. This name can be either a full pathname or a pathname relative to the current working directory. Removing Subdirectories A directory that is to be deleted must be empty (except for the “.” and “..” entries). The root directory can never be deleted. Subdirectories can be removed in the following ways: ■ Using ioctl( ) with the FIORMDIR function and specifying the name of the directory. The file descriptor used can refer to any file or directory on the volume, or to the entire volume itself. ■ Using the remove( ), specifying the name of the directory. ■ Use rmdir( ) from usrFsLib. Reading Directory Entries You can programmatically search directories on HRFS volumes using the opendir( ), readdir( ), rewinddir( ), and closedir( ) routines. To obtain more detailed information about a specific file, use the fstat( ) or stat( ) routine. Along with standard file information, the structure used by these routines also provides the file-attribute byte from a directory entry. For more information, see the API reference for dirLib. 8.4.10 Working with Files This section discusses file I/O and file attributes. File I/O Routines Files on an HRFS file system device are created, deleted, written, and read using the standard VxWorks I/O routines: creat( ), remove( ), write( ), and read( ). For more information, see 7.4 Basic I/O, p.365, and the ioLib API references. 474 8 Local File Systems 8.4 Highly Reliable File System: HRFS Note that and remove( ) is synonymous with unlink( ) for HRFS. File Linking and Unlinking When a link is created an inode is not used. Another directory entry is created at the location specified by the parameter to link( ). In addition, a reference count to the linked file is stored in the file's corresponding inode. When unlinking a file, this reference count is decremented. If the reference count is zero when unlink( ) is called, the file is deleted except if there are open file descriptors open on the file. In this case the directory entry is removed but the file still exists on the disk. This prevents tasks and processes (RTPs) from opening the file. When the final open file descriptor is closed the file is fully deleted freeing its inode. Note that you cannot create a link to a subdirectory only to a regular file. File Permissions HRFS files have POSIX-style permission bits (unlike dosFs files, which have attributes). The bits can be changed using the chmod( ) and fchmod( ) routines. See the API references for more information. 8.4.11 Crash Recovery and Volume Consistency HRFS is a transactional based file system that is designed to be consistent at all times. Crash Recovery If a system unexpectedly loses power or crashes, HRFS rolls back to the last transaction point when the system reboots. The rollback occurs automatically when the file system is mounted. Any changes made after the last complete transaction are lost, but the disk remains in a consistent state. 475 8 VxWorks Kernel Programmer's Guide, 6.6 Consistency Checking An HRFS file system remains in a consistent state for most media (such as hard drives) as long as the underlying hardware is working correctly and never writes an incomplete sector or physical block. This is necessarily true for RAM disks, however, because sector writing is simply a copy of one memory location to another. The write operation may be interrupted before completion if the system loses power or crashes. The hrfsChkDsk( ) routine can, however, be used to check for inconsistencies in the file system. The execution of the disk checker is not automatic; it must be done programmatically. The hrfsChkDsk( ) routine is also useful in relation to hardware problems, and is usually run at boot time for this purpose. 8.4.12 I/O Control Functions Supported by HRFS The HRFS file system supports the ioctl( ) functions. These functions are defined in the header file ioLib.h along with their associated constants; and they are listed in Table 8-1. Table 8-1 I/O Control Functions Supported by HRFS Function Decimal Value Description FIODISKCHANGE 13 Announces a media change. FIODISKFORMAT 5 Formats the disk (device driver function). FIODISKINIT 6 Initializes a file system on a disk volume. FIOFLUSH 2 Flushes the file output buffer. FIOFSTATGET 38 Gets file status information (directory entry data). FIOGETNAME 18 Gets the filename of the fd. FIOMOVE 47 Moves a file (does not rename the file). FIONFREE 30 Gets the number of free bytes on the volume. FIONREAD 1 Gets the number of unread bytes in a file. FIOREADDIR 37 Reads the next directory entry. 476 8 Local File Systems 8.4 Highly Reliable File System: HRFS Table 8-1 I/O Control Functions Supported by HRFS (cont’d) Function Decimal Value Description FIORENAME 10 Renames a file or directory. FIORMDIR 32 Removes a directory. FIOSEEK 7 Sets the current byte offset in a file. FIOSYNC 21 Same as FIOFLUSH, but also re-reads buffered file data. FIOTRUNC 42 Truncates a file to a specified length. FIOUNMOUNT 39 Un-mounts a disk volume. FIOWHERE 8 Returns the current byte position in a file. FIONCONTIG64 50 Gets the maximum contiguous disk space into a 64-bit integer. FIONFREE64 51 Gets the number of free bytes into a 64-bit integer. FIONREAD64 52 Gets the number of unread bytes in a file into a 64-bit integer. FIOSEEK64 53 Sets the current byte offset in a file from a 64-bit integer. FIOWHERE64 54 Gets the current byte position in a file into a 64-bit integer. FIOTRUNC64 55 Set the file's size from a 64-bit integer. 8 For more information, see the API reference for ioctl( ) in ioLib. 477 VxWorks Kernel Programmer's Guide, 6.6 8.5 MS-DOS-Compatible File System: dosFs The dosFs file system is an MS-DOS-compatible file system that offers considerable flexibility appropriate to the multiple demands of real-time applications. The primary features are: ■ Hierarchical files and directories, allowing efficient organization and an arbitrary number of files to be created on a volume. ■ A choice of contiguous or non-contiguous files on a per-file basis. ■ Compatible with widely available storage and retrieval media (diskettes, hard drives, and so on). ■ The ability to boot VxWorks from a dosFs file system. ■ Support for VFAT (Microsoft VFAT long file names) ■ Support for FAT12, FAT16, and FAT32 file allocation table types. For information about dosFs libraries, see the VxWorks API references for dosFsLib and dosFsFmtLib. For information about the MS-DOS file system, please see the Microsoft documentation. dosFs and Flash Memory For information about using dosFs with flash memory, see 10. Flash File System Support: TrueFFS. dosFs and the Transaction-Based Reliable File System Facility The dosFs file system can be used with the transaction-based reliable file system (TRFS) facility; see 7.8.9 Transaction-Based Reliable File System Facility: TRFS, p.405. 8.5.1 Configuring VxWorks for dosFs To include dosFs support in VxWorks, configure the kernel with the appropriate required and optional components. 478 8 Local File Systems 8.5 MS-DOS-Compatible File System: dosFs Required Components The following components are required: INCLUDE_DOSFS_MAIN INCLUDE_DOSFS_FAT INCLUDE_XBD dosFsLib dosFs FAT12/16/32 FAT handler XBD component And, either one or both of the following components are required: INCLUDE_DOSFS_DIR_VFAT Microsoft VFAT direct handler INCLUDE_DOSFS_DIR_FIXED Strict 8.3 & VxLongNames directory handler In addition, you must include the appropriate component for your block device; for example, INCLUDE_ATA. If you are using a device driver that is not designed for use with the XBD facility, you must use the INCLUDE_XBD_BLK_DEV wrapper component in addition to INCLUDE_XBD. See XBD Block Device Wrapper, p.404 for more information. Note that you can use INCLUDE_DOSFS to automatically include the following components: ■ ■ ■ ■ ■ ■ INCLUDE_DOSFS_MAIN INCLUDE_DOSFS_DIR_VFAT INCLUDE_DOSFS_DIR_FIXED INCLUDE_DOSFS_FAT INCLUDE_DOSFS_CHKDSK INCLUDE_DOSFS_FMT Optional dosFs Components The optional dosFs components are: INCLUDE_DOSFS_CACHE INCLUDE_DOSFS_FMT INCLUDE_DOSFS_CHKDSK INCLUDE_DISK_UTIL INCLUDE_TAR disk cache facility dosFs file system formatting module file system integrity checking standard file system operations, such as ls, cd, mkdir, xcopy, and so on the tar utility 479 8 VxWorks Kernel Programmer's Guide, 6.6 Optional XBD Components Optional XBD components are: INCLUDE_XBD_PART_LIB INCLUDE_XBD_TRANS INCLUDE_XBD_RAMDRV disk partitioning facilities TRFS support facility RAM disk facility For information about the XBD facility, see 7.8.8 Extended Block Device Facility: XBD, p.402). 8.5.2 Configuring dosFs Several dosFs component configuration parameters can be used to define how the file system behaves when a dosfs volume is mounted. These parameters are as follows: DOSFS_CHK_ONLY When a dosfs volume is mounted, the media is analyzed for errors, but no repairs are made. DOSFS_CHK_REPAIR Similar to DOSFS_CHK_ONLY, but an attempt to repair the media is made if errors are found. DOSFS_CHK_NONE Media is not checked for errors on mount. DOSFS_CHK_FORCE Used in conjunction with DOSFS_CHK_ONLY and DOSFS_CHK_REPAIR to force a consistency check even if the disk has been marked clean. DOS_CHK_VERB_SILENT or DOS_CHK_VERB_0 dosFs does not to produce any output to the terminal when mounting. DOS_CHK_VERB_1 dosFs produces a minimal amount of output to the terminal when mounting. DOS_CHK_VERB_2 dosFs to produces maximum amount output to the terminal when mounting. Other parameters can be used to configure physical attributes of the file system. They are as follows: 480 8 Local File Systems 8.5 MS-DOS-Compatible File System: dosFs DOSFS_DEFAULT_CREATE_OPTIONS The default parameter for the dosFsLib component. It specifies the action to be taken when a dosFs file system is instantiated. Its default is DOSFS_CHK_NONE. DOSFS_DEFAULT_MAX_FILES The maximum number of files. The default is 20. DOSFS_DEFAULT_DATA_CACHE_SIZE The size of the data cache. The default is 128 KB. DOSFS_DEFAULT_FAT_CACHE_SIZE The size of the FAT cache. The default 16 KB. 8 DOSFS_DEFAULT_DIR_CACHE_SIZE The directory cache size. The default is 64 KB. Caches can be tuned dynamically for individual instances of the file system using the dosFsCacheInfo( ) and dosFsCacheTune( ) routines. The routines dosFsCacheDelete( ) and dosFsCacheCreate( ) can be used to delete and changes the size of caches. To change the size, first delete, and then create. 481 VxWorks Kernel Programmer's Guide, 6.6 8.5.3 Creating a dosFs File System This section describes the process of creating a dosFs file system. It first provides a summary overview and then a detailed description of each step. See 8.5.4 dosFs, ATA Disk, and RAM Disk Examples, p.486 for examples of the steps and code examples. Overview of dosFs File System Creation For information operating system configuration, see 8.5.1 Configuring VxWorks for dosFs, p.478. Note that The file system is initialized automatically at boot time. The steps involved in creating a dosFs file system are as follows: 1. If you are using a custom driver, create the appropriate block device. See Step 1:Create a Block Device, p.462. If you are using a standard VxWorks component for the device, it is created automatically. 2. If you are using a device driver that is not XBD-compliant, create an XBD device wrapper. See Step 2:Create an XBD Device Wrapper, p.483. (Also see XBD Block Device Wrapper, p.404.) 3. Optionally, create and mount partitions. See Step 3:Create Partitions, p.463. 4. If you are not using pre-formatted disks, format the volumes. See Step 4:Formatting the Volume, p.484. 5. Optionally, change the size of the disk cache. See Step 5:Change the Disk Cache Size, p.485. 6. Optionally, check the disk for volume integrity. See Step 6:Check Disk Volume Integrity, p.485. dosFs File System Creation Steps Before any other operations can be performed, the dosFs file system library, dosFsLib, must be initialized. This happens automatically at boot time, triggered by the required dosFs components that were included in the system. Initializing the file system invokes iosDrvInstall( ), which adds the driver to the I/O system driver table. The driver number assigned to the dosFs file system is 482 8 Local File Systems 8.5 MS-DOS-Compatible File System: dosFs recorded in a global variable, dosFsDrvNum. The table specifies the entry points for the dosFs file operations that are accessed by the devices using dosFs. Step 1: Create a Block Device If you are using a standard VxWorks component for the device, it is created automatically. If you are using a custom driver, create the appropriate block device by calling the creation routine for the device driver. The format for this routine is xxxDevCreate( ) where xxx represents the device driver type; for example, scsiBlkDevCreate( ) or ataDevCreate( ). The driver routine returns a pointer to a block device descriptor structure, BLK_DEV. This structure describes the physical attributes of the device and specifies the routines that the device driver provides. The pointer returned is used to create an XBD block device wrapper. For more information on block devices, see TRFS Code Examples, p.408. Step 2: Create an XBD Device Wrapper If you are using a device driver that is not XBD-compliant, it requires an XBD device wrapper. The wrapper is created automatically if you have configured VxWorks with the INCLUDE_XBD_BLK_DEV wrapper component (See XBD Block Device Wrapper, p.404). Otherwise, create a wrapper for each block device using xbdBlkDevCreate( ). After the XBD device wrapper is created the physical device is automatically probed for a file system and partitions. If a disk is already formatted, the disk is mounted. If a a file system is found, it is mounted. If the file system is not dosFs, it must be formatted (see below). Step 3: Create Partitions If you have included the INCLUDE_XBD_PART_LIB component in your system, you can create partitions on a disk and mount volumes atop the partitions. Use the xbdCreatePartition( ) routine to create partitions. This step should only be performed once, when the disk is first initialized. If partitions are already written to the disk, this step should not be performed as it destroys data. 483 8 VxWorks Kernel Programmer's Guide, 6.6 Step 4: Formatting the Volume If you are using unformatted disk or wish to replace the current file system on the disk, format the disk by calling dosFsVolFormat( ). For more information, see the VxWorks API reference for this routine. The MS-DOS and dosFs file systems provide options for the format of the File Allocation Table (FAT) and the format of the directory. These options, described below, are completely independent. ! CAUTION: Reformatting a disk destroys any data that may be on it. File Allocation Table (FAT) Formats A volume FAT format is set during disk formatting, according to either the volume size (by default), or the per-user defined settings passed to dosFsVolFormat( ). FAT options are summarized in Table 8-2: Table 8-2 FAT Formats Format FAT Table Entry SIze Usage Size FAT12 12 bits per cluster number Appropriate for very small devices Typically, each cluster is two with up to 4,084 KB clusters. sectors large. FAT16 16 bits per cluster number Appropriate for small disks of up Typically, used for volumes up to 65,524 KB clusters. to 2 GB; can support up to 8 GB. FAT32 32 bits (only 28 used) Appropriate for medium and per cluster number larger disk drives. By convention, used for volumes larger than 2 GB. Directory Formats The options for the directory format are: ■ MSFT Long Names (VFAT) Uses case-insensitive long filenames, with up to 254 characters. This format accepts disks created with short names. MSFT Long Names1 is the default directory format. 1. The MSFT Long Names (VFAT) format supports 32-bit file size fields, limiting the file size to a 4 GB maximum. 484 8 Local File Systems 8.5 MS-DOS-Compatible File System: dosFs ■ Short Names (8.3) Case-insensitive MS-DOS-style filenames (8.3), with eight uppercase characters for the name itself and three for the extension. Step 5: Change the Disk Cache Size If you have included the INCLUDE_DOSFS_CACHE component, disk caches are automatically created. Three parameters define the size of the data, directory entry, and FAT caches: DOSFS_DEFAULT_DATA_CACHE_SIZE (default 128 KB), DOSFS_DEFAULT_FAT_CACHE_SIZE (default 16 KB), and DOSFS_DEFAULT_DIR_CACHE_SIZE (default 64 KB). In addition, the caches can be tuned dynamically using the dosFsCacheInfo( ) and dosFsCacheTune( ) routines. You can change the size of the cache for a particular instantiation of the file system by first destroying the cache with dosFsCacheDelete( ) and then re-creating the cache with dosFsCacheCreate( ). For more information see the VxWorks API references for these routines. A disk cache is intended to reduce the to reduce the number of accesses to the media. It is not intended for use with RAM disks or TrueFFS. If the cache component is included with TrueFFS, the cache should be removed programmatically with dosFsCacheDelete( ). Step 6: Check Disk Volume Integrity Optionally, check the disk for volume integrity using dosFsChkDsk( ). Disk checking large disks can be time-consuming. The parameter DOSFS_DEFAULT_CREATE_OPTIONS (of the INCLUDE_DOSFS_MAIN component) provides an option for checking the disk, which takes place automatically when the dosfs file system is mounted. This can, however, be a time consuming process and makes the file system inaccessible until the check is complete. Alternatively, the check can be performed programmatically by calling dosFsChkDsk( ). 485 8 VxWorks Kernel Programmer's Guide, 6.6 8.5.4 dosFs, ATA Disk, and RAM Disk Examples This section provides examples of the steps discussed in the preceding section. These examples use a variety of configurations and device types. They are meant to be relatively generic and applicable to most block devices. The examples illustrate the following: ■ Creating and working with a dosFs file system on an ATA disk with commands from the shell. ■ Code that creates and formats partitions. ■ Code that creates and formats a RAM disk volume. The examples in this section require that VxWorks be configured with the INCLUDE_DOSFS_FMT component. One example also relies on the INCLUDE_DOSFS_CACHE component. ! CAUTION: Because device names are recognized by the I/O system using simple substring matching, file systems should not use a slash (/) alone as a name; unexpected results may occur. Example 8-5 Create dosFs for an ATA Disk This example demonstrates how to initialize an ATA disk with dosFs from the shell. While these steps use an XBD-compatible ATA block device, they are applicable to any XBD-compatible block device. 1. If you are using a custom driver, create an ATA block device that controls the master ATA hard disk (drive zero) on the primary ATA controller (controller zero). This device uses the entire disk. -> xbd = ataXbdDevCreate(0,0,0,0,"/ata") New symbol "xbd" added to kernel symbol table. Instantiating /ata:0 as rawFs xbd = 0xca4fe0: value = 262145 = 0x40001 The xbd variable is of type device_t. A value of zero would indicate an error in ataXbdDevCreate( ). Such an error usually indicates a BSP configuration or hardware configuration error. If you are using the standard INCLUDE_ATA device component, the block device is created automatically. Note that in this case the default device name (provided by the component) is /ata0a. 486 8 Local File Systems 8.5 MS-DOS-Compatible File System: dosFs 2. Display information about devices. -> devs drv name 0 /null 1 /tyCo/0 1 /tyCo/1 8 yow-grand: 9 /vio 4 /ata:0 value = 25 = 0x19 The new ata driver /ata:0 is listed. The zero in the name indicates that no partitions were detected. Note that if no file system is detected on the device, the rawFs file system is instantiated automatically and appears the device list. 3. Create two partitions on this disk device, specifying 50% of the disk space for the second partition, leaving 50% for the first partition. This step should only be performed once, when the disk is first initialized. If partitions are already written to the disk, this step should not be performed since it destroys data. -> xbdCreatePartition ("/ata:0", 2, 50, 0, 0) value = 0 = 0x0 4. Then list the devices to display information about the new partitions. -> devs drv name 0 /null 1 /tyCo/0 1 /tyCo/1 8 yow-grand: 9 /vio 3 /ata:1 3 /ata:2 Note that /ata:0 does not appear in this list, and two new devices, /ata:1 and /ata:2, have been added to represent the new partitions. Each volume has rawfs instantiated in it as they are new and unformatted. 487 8 VxWorks Kernel Programmer's Guide, 6.6 5. Format the volumes for dosFs. This step need only be done once, when the volumes are first initialized. If the volumes have already been initialized (formatted), then omit this step. This example formats the file system volumes with default options. -> dosFsVolFormat ("/ata:1", 0, 0) Formatting /ata:1 for DOSFS Instantiating /ata:1 as rawFs Formatting...Retrieved old volume params with %100 confidence: Volume Parameters: FAT type: FAT32, sectors per cluster 8 2 FAT copies, 0 clusters, 38425 sectors per FAT Sectors reserved 32, hidden 0, FAT sectors 76850 Root dir entries 0, sysId (null) , serial number 3a80000 Label:" " ... Disk with 40149184 sectors of 512 bytes will be formatted with: Volume Parameters: FAT type: FAT32, sectors per cluster 8 2 FAT copies, 5008841 clusters, 39209 sectors per FAT Sectors reserved 32, hidden 0, FAT sectors 78418 Root dir entries 0, sysId VX5DOS32, serial number 3a80000 Label:" " ... OK. value = 0 = 0x0 -> dosFsVolFormat ("/ata:2", 0, 0) Formatting /ata:2 for DOSFS Instantiating /ata:2 as rawFs Formatting...Retrieved old volume params with %100 confidence: Volume Parameters: FAT type: FAT32, sectors per cluster 8 2 FAT copies, 0 clusters, 19602 sectors per FAT Sectors reserved 32, hidden 0, FAT sectors 39204 Root dir entries 0, sysId (null) , serial number c78ff000 Label:" " ... Disk with 40144000 sectors of 512 bytes will be formatted with: Volume Parameters: FAT type: FAT32, sectors per cluster 8 2 FAT copies, 5008195 clusters, 39204 sectors per FAT Sectors reserved 32, hidden 0, FAT sectors 78408 Root dir entries 0, sysId VX5DOS32, serial number c78ff000 Label:" " ... OK. value = 0 = 0x0 For more information, see the API reference for dosFsFmtLib. 6. If the INCLUDE_DOSFS_CACHE component is included in VxWorks, 128 KB data, 16 KB directory and a 64 KB FAT cache are created by default. The size of these caches can be changed by removing them and creating a new one. The following example deletes the default caches and creates new ones at twice their size. -> dosFsCacheDelete "/ata:1" value = 0 = 0x0 -> dosFsCacheCreate "/ata:1", 0, 256 * 1024, 0, 32 * 1024, 0, 128 * 1024; value = 0 = 0x0 488 8 Local File Systems 8.5 MS-DOS-Compatible File System: dosFs 7. Display information about the dosFs volumes. -> ll "/ata:1" Listing Directory /ata:1: value = 0 = 0x0 -> ll "/ata:2" Listing Directory /ata:2: value = 0 = 0x0 -> dosFsShow "/ata:2" volume descriptor ptr (pVolDesc): 0xc7c358 XBD device block I/O handle: 0x60001 auto disk check on mount: NOT ENABLED volume write mode: copyback (DOS_WRITE) max # of simultaneously open files: 22 file descriptors in use: 0 # of different files in use: 0 # of descriptors for deleted files: 0 # of obsolete descriptors: 0 8 current volume configuration: - volume label: NO LABEL ; (in boot sector: - volume Id: 0xc78ff000 - total number of sectors: 40,144,000 - bytes per sector: 512 - # of sectors per cluster: 8 - # of reserved sectors: 32 - FAT entry size: FAT32 - # of sectors per FAT copy: 39,204 - # of FAT table copies: 2 - # of hidden sectors: 0 - first cluster is in sector # 78,440 - Update last access date for open-read-close = FALSE - directory structure: VFAT - file name format: 8-bit (extended-ASCII) - root dir start cluster: 2 FAT handler information: ------------------------ allocation group size: - free space on volume: value = 0 = 0x0 ) 501 clusters 20,513,562,620 bytes Above, we can see the Volume parameters for the /ata:2 volume. The file system volumes are now mounted and ready to be used. If you are working with an ATA hard disk or a CD-ROM file system from an ATAPI CD-ROM drive, you can, alternatively, use usrAtaConfig( ). This routine processes several steps at once. For more information, see the API reference. 489 VxWorks Kernel Programmer's Guide, 6.6 Example 8-6 Creating and Partitioning a Disk and Creating Volumes This code example takes a pointer to a block device, creates three partitions, creates the partition handler for these partitions, and creates the dosFs device handler for them. Then, it formats the partitions using dosFsVolFormat( ). STATUS usrPartDiskFsInit ( char * xbdName /* device name used during creation of XBD */ ) { const char * devNames[] = { "/sd0a", "/sd0b", "/sd0c" }; devname_t xbdPartName; int newDataCacheSize = 0x40000 /* 256 KB data cache */ int newFatCacheSize = 0x20000 /* 128 KB FAT cache */ int newDirCacheSize = 0x8000 /* 32 KB Dir cache */ DOSFS_CACHE_INFO cacheParams; int i; /* Map partition names */ for (i = 1; i <= 3; i++) { sprintf (xbdPartName, "%s:d", devNames[i-1],i); fsmNameInstall (devNames[i], xbdPartName); } /* create partitions */ if((xbdCreatePartition (xbdName,3,50,45)) == ERROR) return ERROR; /* Formatting the first partition */ if(dosFsVolFormat (devNames[0], 2,0) == ERROR) return ERROR; /* Re-configure the cache for the first partition */ if (dosFsCacheCreate (devNames[0], NULL, newDataCacheSize, NULL, newDirCacheSize, NULL, newFatCacheSize) == ERROR) return ERROR; /* Retrieve the current data cache tuning parameters and double them */ if (dosFsCacheInfoGet (devNames[0], DOS_DATA_CACHE, &cacheParams) == ERROR) return ERROR; cacheParams.bypass = cacheParams.bypass * 2; cacheParams.readAhead = cacheParams.readAhead * 2; if (dosFsCacheTune (devNames[0], DOS_DATA_CACHE, &cacheParams) == ERROR) return ERROR; 490 8 Local File Systems 8.5 MS-DOS-Compatible File System: dosFs /* Formatting the second partition */ if(dosFsVolFormat (devNames[1], 2,0) == ERROR) return ERROR; /* Formatting the third partition */ if(dosFsVolFormat (devNames[2], 2,0) == ERROR) return ERROR; return OK; } Note that in most cases you would be likely to format the different partitions for different file systems. Example 8-7 Creating and Formatting a RAM Disk Volume The following code creates a RAM disk and formats it for use with the dosFs file system. STATUS usrRamDiskInit ( void ) { int ramDiskSize = 512 * 1024 ; char *ramDiskDevName = "/ram0" ; device_t xbd; /* no argument */ /* 512KB, 512 bytes per sector */ /* 512 byte/sec, no partition support */ xbd = xbdRamDiskDevCreate (512, ramDiskSize, 0, ramDiskDevName); if( xbd == NULL ) return ERROR ; /* format the RAM disk, ignore memory contents */ dosFsVolFormat( ramDiskDevName, DOS_OPT_BLANK | DOS_OPT_QUIET, NULL ); return OK; } 8.5.5 Working with Volumes and Disks This section discusses accessing volume configuration information and synchronizing volumes. For information about ioctl( ) support functions, see 8.5.10 I/O Control Functions Supported by dosFsLib, p.500. 491 8 VxWorks Kernel Programmer's Guide, 6.6 Accessing Volume Configuration Information The dosFsShow( ) routine can be used to display volume configuration information from the shell. The dosFsVolDescGet( ) routine can be used programmatically obtain or verify a pointer to the DOS_VOLUME_DESC structure. For more information, see the API references for these routines. Synchronizing Volumes When a disk is synchronized, all modified buffered data is physically written to the disk, so that the disk is up to date. This includes data written to files, updated directory information, and the FAT. To avoid loss of data, a disk should be synchronized before it is removed. For more information, see the API references for close( ) and dosFsVolUnmount( ). 8.5.6 Working with Directories This section discusses creating and removing directories, and reading directory entries. Creating Subdirectories For FAT32, subdirectories can be created in any directory at any time. For FAT12 and FAT16, subdirectories can be created in any directory at any time, except in the root directory once it reaches its maximum entry count. Subdirectories can be created in the following ways: ■ Using ioctl( ) with the FIOMKDIR function. The name of the directory to be created is passed as a parameter to ioctl( ). ■ Using open( ). To create a directory, the O_CREAT option must be set in the flags parameter and the FSTAT_DIR option must be set in the mode parameter. The open( ) call returns a file descriptor that describes the new directory. Use this file descriptor for reading only, and close it when it is no longer needed. ■ Use mkdir( ) from usrFsLib. When creating a directory using any of the above methods, the new directory name must be specified. This name can be either a full pathname or a pathname relative to the current working directory. 492 8 Local File Systems 8.5 MS-DOS-Compatible File System: dosFs Removing Subdirectories A directory that is to be deleted must be empty (except for the “.” and “..” entries). The root directory can never be deleted. Subdirectories can be removed in the following ways: ■ Using ioctl( ) with the FIORMDIR function, specifying the name of the directory. The file descriptor used can refer to any file or directory on the volume, or to the entire volume itself. ■ Using the remove( ) function, specifying the name of the directory. ■ Use rmdir( ) from usrFsLib. 8 Reading Directory Entries You can programmatically search directories on dosFs volumes using the opendir( ), readdir( ), rewinddir( ), and closedir( ) routines. To obtain more detailed information about a specific file, use the fstat( ) or stat( ) routine. Along with standard file information, the structure used by these routines also returns the file-attribute byte from a directory entry. For more information, see the API reference for dirLib. 8.5.7 Working with Files This section discusses file I/O and file attributes. File I/O Routines Files on a dosFs file system device are created, deleted, written, and read using the standard VxWorks I/O routines: creat( ), remove( ), write( ), and read( ). For more information, see 7.4 Basic I/O, p.365, and the ioLib API references. File Attributes The file-attribute byte in a dosFs directory entry consists of a set of flag bits, each indicating a particular file characteristic. The characteristics described by the file-attribute byte are shown in Table 8-3. 493 VxWorks Kernel Programmer's Guide, 6.6 Table 8-3 Flags in the File-Attribute Byte VxWorks Flag Name Hex Value Description DOS_ATTR_RDONLY 0x01 read-only file DOS_ATTR_HIDDEN 0x02 hidden file DOS_ATTR_SYSTEM 0x04 system file DOS_ATTR_VOL_LABEL 0x08 volume label DOS_ATTR_DIRECTORY 0x10 subdirectory DOS_ATTR_ARCHIVE 0x20 file is subject to archiving DOS_ATTR_RDONLY If this flag is set, files accessed with open( ) cannot be written to. If the O_WRONLY or O_RDWR flags are set, open( ) returns ERROR, setting errno to S_dosFsLib_READ_ONLY. DOS_ATTR_HIDDEN This flag is ignored by dosFsLib and produces no special handling. For example, entries with this flag are reported when searching directories. DOS_ATTR_SYSTEM This flag is ignored by dosFsLib and produces no special handling. For example, entries with this flag are reported when searching directories. DOS_ATTR_VOL_LABEL This is a volume label flag, which indicates that a directory entry contains the dosFs volume label for the disk. A label is not required. If used, there can be only one volume label entry per volume, in the root directory. The volume label entry is not reported when reading the contents of a directory (using readdir( )). It can only be determined using the ioctl( ) function FIOLABELGET. The volume label can be set (or reset) to any string of 11 or fewer characters, using the ioctl( ) function FIOLABELSET. Any file descriptor open to the volume can be used during these ioctl( ) calls. DOS_ATTR_DIRECTORY This is a directory flag, which indicates that this entry is a subdirectory, and not a regular file. DOS_ATTR_ARCHIVE This is an archive flag, which is set when a file is created or modified. This flag is intended for use by other programs that search a volume for modified files 494 8 Local File Systems 8.5 MS-DOS-Compatible File System: dosFs and selectively archive them. Such a program must clear the archive flag, since VxWorks does not. All the flags in the attribute byte, except the directory and volume label flags, can be set or cleared using the ioctl( ) function FIOATTRIBSET. This function is called after the opening of the specific file with the attributes to be changed. The attribute-byte value specified in the FIOATTRIBSET call is copied directly; to preserve existing flag settings, determine the current attributes using stat( ) or fstat( ), then change them using bitwise AND and OR operators. Example 8-8 Setting DosFs File Attributes This example makes a dosFs file read-only, and leaves other attributes intact. STATUS changeAttributes ( void ) { int fd; struct stat statStruct; /* open file */ if ((fd = open ("file", O_RDONLY, 0)) == ERROR) return (ERROR); /* get directory entry data */ if (fstat (fd, &statStruct) == ERROR) return (ERROR); /* set read-only flag on file */ if (ioctl (fd, FIOATTRIBSET, (statStruct.st_attrib | DOS_ATTR_RDONLY)) == ERROR) return (ERROR); /* close file */ close (fd); return (OK); } NOTE: You can also use the attrib( ) routine to change file attributes. For more information, see the entry in usrFsLib. 495 8 VxWorks Kernel Programmer's Guide, 6.6 8.5.8 Disk Space Allocation Options The dosFs file system allocates disk space using one of the following methods. The first two methods are selected based upon the size of the write operation. The last method must be manually specified. ■ single cluster allocation Single cluster allocation uses a single cluster, which is the minimum allocation unit. This method is automatically used when the write operation is smaller than the size of a single cluster. ■ cluster group allocation (nearly contiguous) Cluster group allocation uses adjacent (contiguous) groups of clusters, called extents. Cluster group allocation is nearly contiguous allocation and is the default method used when files are written in units larger than the size of a disk’s cluster. ■ absolutely contiguous allocation Absolutely contiguous allocation uses only absolutely contiguous clusters. Because this type of allocation is dependent upon the existence of such space, it is specified under only two conditions: immediately after a new file is created and when reading from a file assumed to have been allocated to a contiguous space. Using this method risks disk fragmentation. For any allocation method, you can deallocate unused reserved bytes by using the POSIX-compliant routine ftruncate( ) or the ioctl( ) function FIOTRUNC. Choosing an Allocation Method Under most circumstances, cluster group allocation is preferred to absolutely contiguous file access. Because it is nearly contiguous file access, it achieves a nearly optimal access speed. Cluster group allocation also significantly minimizes the risk of fragmentation posed by absolutely contiguous allocation. Absolutely contiguous allocation attains raw disk throughput levels, however this speed is only slightly faster than nearly contiguous file access. Moreover, fragmentation is likely to occur over time. This is because after a disk has been in use for some period of time, it becomes impossible to allocate contiguous space. Thus, there is no guarantee that new data, appended to a file created or opened with absolutely continuous allocation, will be contiguous to the initially written data segment. 496 8 Local File Systems 8.5 MS-DOS-Compatible File System: dosFs It is recommended that for a performance-sensitive operation, the application regulate disk space utilization, limiting it to 90% of the total disk space. Fragmentation is unavoidable when filling in the last free space on a disk, which has a serious impact on performance. Using Cluster Group Allocation The dosFs file system defines the size of a cluster group based on the media’s physical characteristics. That size is fixed for each particular media. Since seek operations are an overhead that reduces performance, it is desirable to arrange files so that sequential portions of a file are located in physically contiguous disk clusters. Cluster group allocation occurs when the cluster group size is considered sufficiently large so that the seek time is negligible compared to the read/write time. This technique is sometimes referred to as nearly contiguous file access because seek time between consecutive cluster groups is significantly reduced. Because all large files on a volume are expected to have been written as a group of extents, removing them frees a number of extents to be used for new files subsequently created. Therefore, as long as free space is available for subsequent file storage, there are always extents available for use. Thus, cluster group allocation effectively prevents fragmentation (where a file is allocated in small units spread across distant locations on the disk). Access to fragmented files can be extremely slow, depending upon the degree of fragmentation. Using Absolutely Contiguous Allocation A contiguous file is made up of a series of consecutive disk sectors. Absolutely contiguous allocation is intended to allocate contiguous space to a specified file (or directory) and, by so doing, optimize access to that file. You can specify absolutely contiguous allocation either when creating a file, or when opening a file previously created in this manner. For more information on the ioctl( ) functions, see 8.5.10 I/O Control Functions Supported by dosFsLib, p.500. 497 8 VxWorks Kernel Programmer's Guide, 6.6 Allocating Contiguous Space for a File To allocate a contiguous area to a newly created file, follow these steps: 1. First, create the file in the normal fashion using open( ) or creat( ). 2. Then, call ioctl( ). Use the file descriptor returned from open( ) or creat( ) as the file descriptor argument. Specify FIOCONTIG as the function code argument and the size of the requested contiguous area, in bytes, as the third argument. The FAT is then searched for a suitable section of the disk. If found, this space is assigned to the new file. The file can then be closed, or it can be used for further I/O operations. The file descriptor used for calling ioctl( ) should be the only descriptor open to the file. Always perform the ioctl( ) FIOCONTIG operation before writing any data to the file. To request the largest available contiguous space, use CONTIG_MAX for the size of the contiguous area. For example: status = ioctl (fd, FIOCONTIG, CONTIG_MAX); Allocating Space for Subdirectories Subdirectories can also be allocated a contiguous disk area in the same manner: ■ If the directory is created using the ioctl( ) function FIOMKDIR, it must be subsequently opened to obtain a file descriptor to it. ■ If the directory is created using options to open( ), the returned file descriptor from that call can be used. A directory must be empty (except for the “.” and “..” entries) when it has contiguous space allocated to it. Opening and Using a Contiguous File Fragmented files require following cluster chains in the FAT. However, if a file is recognized as contiguous, the system can use an enhanced method that improves performance. This applies to all contiguous files, whether or not they were explicitly created using FIOCONTIG. Whenever a file is opened, it is checked for contiguity. If it is found to be contiguous, the file system registers the necessary information about that file to avoid the need for subsequent access to the FAT table. This enhances performance when working with the file by eliminating seek operations. When you are opening a contiguous file, you can explicitly indicate that the file is contiguous by specifying the DOS_O_CONTIG_CHK flag with open( ). This 498 8 Local File Systems 8.5 MS-DOS-Compatible File System: dosFs prompts the file system to retrieve the section of contiguous space, allocated for this file, from the FAT table. To find the maximum contiguous area on a device, you can use the ioctl( ) function FIONCONTIG. This information can also be displayed by dosFsConfigShow( ). Example 8-9 Finding the Maximum Contiguous Area on a DosFs Device In this example, the size (in bytes) of the largest contiguous area is copied to the integer pointed to by the third parameter to ioctl( ) (count). STATUS contigTest ( void ) { int count; int fd; 8 /* no argument */ /* size of maximum contiguous area in bytes */ /* file descriptor */ /* open device in raw mode */ if ((fd = open ("/DEV1/", O_RDONLY, 0)) == ERROR) return (ERROR); /* find max contiguous area */ ioctl (fd, FIONCONTIG, &count); /* close device and display size of largest contiguous area */ close (fd); printf ("largest contiguous area = %d\n", count); return (OK); } 8.5.9 Crash Recovery and Volume Consistency The DOS file system is inherently susceptible to data structure inconsistencies that result from interruptions during certain types of disk updates. These types of interruptions include power failures, system crashes (for fixed disks), and the manual removal of a disk. NOTE: The DOS file system is not considered a fault-tolerant file system. The VxWorks dosFs file system, however, can be used in conjunction with the Transaction-Based Reliable File System facility; see 7.8.9 Transaction-Based Reliable File System Facility: TRFS, p.405. 499 VxWorks Kernel Programmer's Guide, 6.6 Inconsistencies occur because the file system data for a single file is stored in three separate regions of the disk. The data stored in these regions are: ■ The file chain in the File Allocation Table (FAT), located in a region near the beginning of the disk. ■ The directory entry, located in a region that could be anywhere on the disk. ■ File clusters containing file data, that could be located anywhere on the disk. Since all three regions are not always updated before an interruption, dosFs includes an optional integrated consistency-checking mechanism to detect and recover from inconsistencies. For example, if a disk is removed when a file is being deleted, a consistency check completes the file deletion operation. Or, if a file is being created when an interruption occurs, then the file is un-created. In other words, the consistency checker either rolls forward or rolls back the operation that experienced the inconsistency, making whichever correction is possible. 8.5.10 I/O Control Functions Supported by dosFsLib The dosFs file system supports the ioctl( ) functions. These functions are defined in the header file ioLib.h along with their associated constants, and they are described in Table 8-4. Table 8-4 I/O Control Functions Supported by dosFsLib Function Decimal Value Description FIOATTRIBSET 35 Sets the file-attribute byte in the dosFs directory entry. FIOCONTIG 36 Allocates contiguous disk space for a file or directory. FIODISKCHANGE 13 Announces a media change. FIODISKFORMAT 5 Formats the disk (device driver function). FIODISKINIT 6 Initializes a dosFs file system on a disk volume. FIOFLUSH 2 Flushes the file output buffer. FIOFSTATGET 38 Gets file status information (directory entry data). FIOGETNAME 18 Gets the filename of the fd. FIOLABELGET 33 Gets the volume label. 500 8 Local File Systems 8.5 MS-DOS-Compatible File System: dosFs Table 8-4 I/O Control Functions Supported by dosFsLib (cont’d) Function Decimal Value Description FIOLABELSET 34 Sets the volume label. FIOMKDIR 31 Creates a new directory. FIOMOVE 47 Moves a file (does not rename the file). FIONCONTIG 41 Gets the size of the maximum contiguous area on a device. FIONFREE 30 Gets the number of free bytes on the volume. FIONREAD 1 Gets the number of unread bytes in a file. FIOREADDIR 37 Reads the next directory entry. FIORENAME 10 Renames a file or directory. FIORMDIR 32 Removes a directory. FIOSEEK 7 Sets the current byte offset in a file. FIOSYNC 21 Same as FIOFLUSH, but also re-reads buffered file data. FIOTRUNC 42 Truncates a file to a specified length. FIOUNMOUNT 39 Un-mounts a disk volume. FIOWHERE 8 Returns the current byte position in a file. FIOCONTIG64 49 Allocates contiguous disk space using a 64-bit size. FIONCONTIG64 50 Gets the maximum contiguous disk space into a 64-bit integer. FIONFREE64 51 Gets the number of free bytes into a 64-bit integer. FIONREAD64 52 Gets the number of unread bytes in a file into a 64-bit integer. FIOSEEK64 53 Sets the current byte offset in a file from a 64-bit integer. 8 501 VxWorks Kernel Programmer's Guide, 6.6 Table 8-4 I/O Control Functions Supported by dosFsLib (cont’d) Function Decimal Value Description FIOWHERE64 54 Gets the current byte position in a file into a 64-bit integer. FIOTRUNC64 55 Set the file's size from a 64-bit integer. For more information, see the API references for dosFsLib and for ioctl( ) in ioLib. 502 8 Local File Systems 8.5 MS-DOS-Compatible File System: dosFs 8.5.11 Booting from a Local dosFs File System Using SCSI VxWorks can be booted from a local SCSI device (such as a hard drive in the target system). Before you can boot from SCSI, you must make a new boot loader that contains the SCSI library. Configure VxWorks with the INCLUDE_SCSI, INCLUDE_SCSI_BOOT, and SYS_SCSI_CONFIG components. After creating the SCSI boot loader ROM, you can prepare the dosFs file system for use as a boot device. The simplest way to do this is to partition the SCSI device so that a dosFs file system starts at block 0. You can then make the new system image, place it on your SCSI boot device, and boot the new VxWorks system. These steps are shown in more detail below. ! Step 1: WARNING: For use as a boot device, the directory name for the dosFs file system must begin and end with slashes (as with /sd0/ used in the following example). This is an exception to the usual naming convention for dosFs file systems and is incompatible with the NFS requirement that device names not end in a slash. Create the SCSI Device Create the SCSI device using scsiPhysDevCreate( ) and initialize the disk with a dosFs file system. Modify the file installDir/vxworks-6.x/target/bspName/sysScsi.c to reflect your SCSI configuration. Step 2: Rebuild Your System Rebuild your system. Step 3: Copy the VxWorks Run-time Image Copy the file vxWorks to the drive. Below, a VxWorks task spawns the copy( ) routine, passing it two arguments. The first argument is the source file for the copy( ) command. The source file is the VxWorks run-time image, vxWorks. The source host name is tiamat:, the source filename is C:/vxWorks. These are passed to copy( ) in concatenated form, as the string “tiamat:C:/vxWorks.” The second argument is the destination file for the copy( ) command. The dosFs file system, on the local target SCSI disk device, is named /sd0, and the target file name is vxWorks. These are, similarly, passed to copy( ) in concatenated form, as the string “/sd0/vxWorks.” When booting the target from the SCSI device, the boot loader image should specify the run-time file as “/sd0/vxWorks”. 503 8 VxWorks Kernel Programmer's Guide, 6.6 -> sp (copy, "tiamat:c:/vxWorks","/sd0/vxWorks") task spawned: id = 0x3f2a200, name = t2 value = 66232832 = 0x3f2a200 Copy OK: 1065570 bytes copied Step 4: Copy the System Symbol Table Depending upon image configuration, the vxWorks.sym file for the system symbol table may also be needed. Therefore, in similar fashion, copy the vxWorks.sym file. The run-time image, vxWorks, downloads the vxWorks.sym file from the same location. -> sp (copy, "tiamat:c:/vxWorks.sym","/sd0/vxWorks.sym") task spawned: id = 0x3f2a1bc, name = t3 value = 66232764 = 0x3f2a1bc Copy OK: 147698 bytes copied Step 5: Test the Copying Now, list the files to ensure that the files were correctly copied. -> sp (ll, "/sd0") task spawned: id = 0x3f2a1a8, name = t4 value = 66232744 = 0x3f2a1a8 -> Listing Directory /sd0: -rwxrwxrwx 1 0 0 -rwxrwxrwx 1 0 0 Step 6: 1065570 Oct 26 2001 vxWorks 147698 Oct 26 2001 vxWorks.sym Reboot and Change Parameters Reboot the system, and then change the boot loader parameters. Boot device parameters for SCSI devices follow this format: scsi=id,lun where id is the SCSI ID of the boot device, and lun is its Logical Unit Number (LUN). To enable use of the network, include the on-board Ethernet device (for example, ln for LANCE) in the other field. The following example boots from a SCSI device with a SCSI ID of 2 and a LUN of 0. 504 8 Local File Systems 8.6 Raw File System: rawFs boot device processor number host name file name inet on ethernet (e) host inet (h) user (u) flags (f) target name (tn) other : : : : : : : : : : scsi=2,0 0 host /sd0/vxWorks 147.11.1.222:ffffff00 147.11.1.3 jane 0x0 t222 ln 8 8.6 Raw File System: rawFs VxWorks provides a raw file system (rawFs) for use in systems that require only the most basic disk I/O functions. The rawFs file system, implemented with rawFsLib, treats the entire disk volume much like a single large file. Although the dosFs file system provides this ability to varying degrees, the rawFs file system offers advantages in size and performance if more complex functions are not required. The rawFs file system imposes no organization of the data on the disk. It maintains no directory information; and there is therefore no division of the disk area into specific files. All open( ) operations on rawFs devices specify only the device name; no additional filenames are possible. The entire disk area is treated as a single file and is available to any file descriptor that is open for the device. All read and write operations to the disk use a byte-offset relative to the start of the first block on the disk. A rawFs file system is created by default if inserted media does not contain a recognizable file system. 8.6.1 Configuring VxWorks for rawFs To use the rawFs file system, configure VxWorks with the INCLUDE_RAWFS and INCLUDE_XBD components. If you are using a device driver that is not designed for use with the XBD facility, you must use the INCLUDE_XBD_BLK_DEV wrapper component in addition to INCLUDE_XBD. See XBD Block Device Wrapper, p.404 for more information. 505 VxWorks Kernel Programmer's Guide, 6.6 Set the NUM_RAWFS_FILES parameter of the INCLUDE_RAWFS component to the desired maximum open file descriptor count. For information about using multiple file descriptors with what is essentially a single large file, see 8.6.4 rawFs File I/O, p.509. 8.6.2 Creating a rawFs File System The rawFs file system is the default file system. It is created automatically when VxWorks cannot instantiate a known file system such as dosFs, HRFS, or cdromFs. Unlike dosFs and HRFS, rawFs does not have a formatter. There are no particular data structures on the media that signify the disk as being raw. To create a rawFs file system manually, the current file system must be un-instantiated and replaced with rawFs. Having two or more file systems on the same media can produce instabilities in the VxWorks system. Hence, when instantiating a new file system the previous one must be removed. See Example 8-10Creating a rawFs File System, p.508 for code that illustrates how this can be done. (See 8.2 File System Monitor, p.455 for information about default creation of rawFs.) The rawFs library rawFsLib is initialized automatically at boot time. The rawFsInit( ) routine is called by the usrRoot( ) task after starting the VxWorks system. The rawFsInit( ) routine takes a single parameter, the maximum number of rawFs file descriptors that can be open at one time. This count is used to allocate a set of descriptors; a descriptor is used each time a rawFs device is opened. The parameter can be set with the NUM_RAWFS_FILES configuration parameter of the INCLUDE_RAWFS component The rawFsInit( ) routine also makes an entry for the rawFs file system in the I/O system driver table (with iosDrvInstall( )). This entry specifies the entry points for rawFs file operations, for all devices that use the rawFs file system. The driver number assigned to the rawFs file system is placed in a global variable, rawFsDrvNum. After the rawFs file system is initialized, one or more devices must be created. Devices are created with the device driver’s device creation routine (xxDevCreate( )). The driver routine returns a pointer to a block device descriptor structure (BLK_DEV). The BLK_DEV structure describes the physical aspects of the device and specifies the routines in the device driver that a file system can call. Immediately after its creation, the block device has neither a name nor a file system associated with it. To initialize a block device for use with rawFs, the already-created block device must be associated with rawFs and a name must be 506 8 Local File Systems 8.6 Raw File System: rawFs assigned to it. This is done with the rawFsDevInit( ) routine. Its parameters are the name to be used to identify the device and a pointer to the block device descriptor structure (BLK_DEV): RAW_VOL_DESC *pVolDesc; BLK_DEV *pBlkDev; pVolDesc = rawFsDevInit ("DEV1:", pBlkDev); The rawFsDevInit( ) call assigns the specified name to the device and enters the device in the I/O system device table (with iosDevAdd( )). It also allocates and initializes the file system’s volume descriptor for the device. It returns a pointer to the volume descriptor to the caller; this pointer is used to identify the volume during certain file system calls. Note that initializing the device for use with rawFs does not format the disk. That is done using an ioctl( ) call with the FIODISKFORMAT function. NOTE: No disk initialization (FIODISKINIT) is required, because there are no file system structures on the disk. Note, however, that rawFs accepts that ioctl( ) function code for compatibility with other file systems; in such cases, it performs no action and always returns OK. 507 8 VxWorks Kernel Programmer's Guide, 6.6 Example 8-10 Creating a rawFs File System This example illustrates creating a rawFs file system. int fd; device_t xbd; /* Map some XBD names. Use :0 and :1 since the disk may or may not have partitions */ fsmNameMap ("/ata:0", "/rawfs"); fsmNameMap ("/ata:1", "/rawfs"); xbd = ataXbdDevCreate (0,0,0,0,"/ata"); /* Get an file descriptor to the current file system */ fd = open ("/rawfs", 0, 0); /* Register on the path instantiator event */ /* The ejection of the current file system is asynchronous and is handled by another task. Depending on relative priorities this may not happen immediately so the path wait even facility is used. Each file system will trip this event when they instatiate to let waiting task that it is ready. */ fsPathAddedEventSetup (&waitData, "/rawfs"); fd = open ("/rawfs", 0, 0); /* Eject the current file system and put rawfs in its place */ ioctl (fd, XBD_SOFT_EJECT, (int)XBD_TOP); /* Our FD is now invalid */ /* Wait for the path to instantiate */ fsWaitForPath(&waitData); Once the call to fsWaitForPath( ) returns the rawfs file system is ready. 8.6.3 Mounting rawFs Volumes A disk volume is mounted automatically, generally during the first open( ) or creat( ) operation. (Certain ioctl( ) functions also cause the disk to be mounted.) The volume is again mounted automatically on the first disk access following a ready-change operation. ! CAUTION: Because device names are recognized by the I/O system using simple substring matching, file systems should not use a slash (/) alone as a name or unexpected results may occur. 508 8 Local File Systems 8.6 Raw File System: rawFs 8.6.4 rawFs File I/O To begin I/O operations upon a rawFs device, first open the device using the standard open( ) routine (or the creat( ) routine). Data on the rawFs device is written and read using the standard I/O routines write( ) and read( ). For more information, see 7.4 Basic I/O, p.365. The character pointer associated with a file descriptor (that is, the byte offset where the read and write operations take place) can be set by using ioctl( ) with the FIOSEEK function. Multiple file descriptors can be open simultaneously for a single device. These must be carefully managed to avoid modifying data that is also being used by another file descriptor. In most cases, such multiple open descriptors use FIOSEEK to set their character pointers to separate disk areas. 8.6.5 I/O Control Functions Supported by rawFsLib The rawFs file system supports the ioctl( ) functions shown in Table 8-5. The functions listed are defined in the header file ioLib.h. For more information, see the API references for rawFsLib and for ioctl( ) in ioLib. Table 8-5 I/O Control Functions Supported by rawFsLib Function Decimal Value Description FIODISKCHANGE 13 Announces a media change. FIODISKFORMAT 5 Formats the disk (device driver function). FIOFLUSH 2 Same as FIOSYNC. FIOGETNAME 18 Gets the device name of the fd. FIONREAD 1 Gets the number of unread bytes on the device. FIOSEEK 7 Sets the current byte offset on the device. FIOSYNC 21 Writes out all modified file descriptor buffers. FIOUNMOUNT 39 Un-mounts a disk volume. FIOWHERE 8 Returns the current byte position on the device. 509 8 VxWorks Kernel Programmer's Guide, 6.6 8.7 CD-ROM File System: cdromFs The VxWorks CD-ROM file system, cdromFs allows applications to read data from CDs formatted according to the ISO 9660 standard file system with or without the Joliet extensions. This section describes how cdromFs is organized, configured, and used. The cdromFs library, cdromFsLib, lets applications read any CD-ROMs, CD-Rs, or CD-RWs (collectively called CDs) that are formatted in accordance with the ISO 9660 file system standard, with or without the Joliet extensions. ISO 9660 interchange level 3, implementation level 2, is supported. Note that multi-extent files, interleaved files, and files with extended attribute records are supported. The following CD features and ISO 9660 features are not supported: ■ ■ ■ ■ Multi-volume sets Record format files CDs with a sector size that is not a power of two2 Multi-session CD-R or CD-RW3 After initializing cdromFs and mounting it on a CD-ROM block device, you can access data on that device using the standard POSIX I/O calls: open( ), close( ), read( ), ioctl( ), readdir( ), and stat( ). The write( ) call always returns an error. The cdromFs utility supports multiple drives, multiple open files, and concurrent file access. When you specify a pathname, cdromFS accepts both forward slashes (/) and back slashes (\) as path delimiters. However, the backslash is not recommended because it might not be supported in future releases. The initialization sequence for the cdromFs file system is similar to installing a dosFs file system on a SCSI or ATA device. After you have created the CD file system device (8.7.2 Creating and Using cdromFs, p.512), use ioctl( ) to set file system options. The files system options are described below: CDROMFS_DIR_MODE_SET/GET These options set and get the directory mode. The directory mode controls whether a file is opened with the Joliet extensions, or without them. The directory mode can be set to any of the following: 2. Therefore, mode 2/form 2 sectors are not supported, as they have 2324 bytes of user data per sector. Both mode 1/form 1 and mode 2/form 1 sectors are supported, as they have 2048 bytes of user data per sector. 3. The first session (that is, the earliest session) is always read. The most commonly desired behavior is to read the last session (that is, the latest session). 510 8 Local File Systems 8.7 CD-ROM File System: cdromFs MODE_ISO9660 Do not use the Joliet extensions. MODE_JOLIET Use the Joliet extensions. MODE_AUTO Try opening the directory first without Joliet, and then with Joliet. ! CAUTION: Changing the directory mode un-mounts the file system. Therefore, any open file descriptors are marked as obsolete. CDROMFS_STRIP_SEMICOLON 8 This option sets the readdir( ) strip semicolon setting to FALSE if arg is 0, and to TRUE otherwise. If TRUE, readdir( ) removes the semicolon and following version number from the directory entries retrieved. CDROMFS_GET_VOL_DESC This option returns, in arg, the primary or supplementary volume descriptor by which the volume is mounted. arg must be of type T_ISO_PVD_SVD_ID, as defined in cdromFsLib.h. The result is the volume descriptor, adjusted for the endianness of the processor (not the raw volume descriptor from the CD). This result can be used directly by the processor. The result also includes some information not in the volume descriptor, such as which volume descriptor is in use. For information on using cdromFs( ), see the API reference for cdromFsLib. 8.7.1 Configuring VxWorks for cdromFs To configure VxWorks with cdromFs, add the INCLUDE_CDROMFS and INCLUDE_XBD components to the kernel. Add other required components (such as SCSI or ATA) depending on the type of device). If you are using a device driver that is not designed for use with the XBD facility, you must use the INCLUDE_XBD_BLK_DEV wrapper component in addition to INCLUDE_XBD. See XBD Block Device Wrapper, p.404 for more information. If you are using an ATAPI device, make appropriate modifications to the ataDrv, ataResources[ ] structure array (if needed). This must be configured appropriately for your hardware platform. 511 VxWorks Kernel Programmer's Guide, 6.6 8.7.2 Creating and Using cdromFs This section describes the steps for creating a block device for the CD-ROM, creating a cdromFsLib device, mounting the file system, and accessing the media. The steps are performed from the shell, and shell show routines are used to display information. Step 1: Create a Block Device Create a block device. The following is an example for an ATAPI master device upon the secondary ATA controller: -> xbd = ataXbdDevCreate(1,0,0,0,"/cdrom") New symbol "xbd" added to kernel symbol table. xbd = 0xca4fe0: value = 262145 = 0x4000 CDROMFS file system is created automatically if a CD is present in the drive. Step 2: Verify cdromFs is instantiated If a CD is present in the drive, the device name appears in the devs output. -> devs drv name 0 /null 1 /tyCo/0 1 /tyCo/1 4 /fd0 5 /ata0a 9 yow-grand: 10 /vio 3 /cdrom:0 Step 3: Open the Root Directory This step is optional. It is only required if you plan to perform Step 4 or Step 5, both of which use the file descriptor obtained in this step. -> fd = open ("/cdrom:0", 0, 0) New symbol "fd" added to kernel symbol table. fd = 0x18cef98: value = 4 = 0x4 In the command-line sequence above, the first 0 is the value of O_RDONLY in fcntl.h. Remember to close the root directory in Step 6. Step 4: Set readdir( ) To Omit Version Numbers from Its Output This step is optional. 512 8 Local File Systems 8.7 CD-ROM File System: cdromFs The strip semicolon mode controls whether readdir( ) returns version numbers. After mounting, the strip semicolon mode defaults to FALSE, meaning that version numbers will be returned. If you do not want version numbers, type the following: -> ioctl (fd, 0x740002, 1) In the command-line sequence above, 0x740002 is the value of CDROMFS_STRIP_SEMICOLON in cdromFsLib.h. Step 5: Specify Which Volume Descriptor To Use This step is optional. The directory mode controls which volume descriptor is used to open a file or directory. After mounting, the directory mode defaults to MODE_AUTO, meaning that all volume descriptors will be tried. The directory mode can be changed to MODE_ISO9660 to use only the ISO 9660 volume descriptors, or to MODE_JOLIET to use only the Joliet volume descriptors. If either of these modes is selected, and if the CD does not contain the selected volume descriptor, an S_cdromFsLib_UNKNOWN_FILE_SYSTEM error is recorded. -> ioctl (fd, 0x740000, 0) In the command-line sequence above, 0x740000 is the value of CDROMFS_DIR_MODE_SET, and 0 is the value of MODE_ISO9660. Both are located in cdromFsLib.h. Step 6: Close the Root Directory This step is required only if you opened the root directory in Step 3. -> close (fd) 513 8 VxWorks Kernel Programmer's Guide, 6.6 Step 7: Check the Configuration You can check the CD-ROM configuration using cdromFsVolConfigShow( ): -> cdromFsVolConfigShow "/cdrom:0" device config structure ptr device name bytes per physical sector 0x18d4dd8 /cdrom:0 2048 Primary directory hierarchy: 514 volume descriptor number descriptor logical sector descriptor offset in sector standard ID volume descriptor version UCS unicode level (0=ISO9660) system ID volume ID volume size number of logical blocks volume set size volume sequence number logical block size path table memory size (bytes) path table size on CD (bytes) path table entries volume set ID :1 :16 :0 :CD001 :1 :0 : :DELL_P1110 :37773312 = 36 MB :18444 = 0x480c :1 :1 :2048 :364 :364 :21 : volume publisher ID : volume data preparer ID : volume application ID :NERO - BURNING ROM copyright file name abstract file name bibliographic file name creation date modification date expiration date effective date value = 0 = 0x0 :none :none :none :13.07.2000 :13.07.2000 :00.00.0000 :00.00.0000 12:30:00:00 12:30:00:00 00:00:00:00 00:00:00:00 8 Local File Systems 8.7 CD-ROM File System: cdromFs 8.7.3 I/O Control Functions Supported by cdromFsLib The cdromFs file system supports the ioctl( ) functions. These functions, and their associated constants, are defined in the header files ioLib.h and cdromFsLib.h. Table 8-6 describes the ioctl( ) functions that cdromFsLib supports. For more information, see the API references for cdromFsLib and for ioctl( ) in ioLib. Table 8-6 ioctl( ) Functions Supported by cdromFsLib Function Constant Decimal Description CDROMFS_DIR_MODE_GET 7602176 Gets the volume descriptor(s) used to open files. CDROMFS_DIR_MODE_SET 7602177 Sets the volume descriptor(s) used to open files. CDROMFS_GET_VOL_DESC 7602179 Gets the volume descriptor that is currently in use. CDROMFS_STRIP_SEMICOLON 7602178 Sets the readdir( ) strip version number setting. FIOFSTATGET 38 Gets file status information (directory entry data). FIOGETNAME 18 Gets the filename of the file descriptor. FIOLABELGET 33 Gets the volume label. FIONREAD 1 Gets the number of unread bytes in a file. FIONREAD64 52 Gets the number of unread bytes in a file (64-bit version). FIOREADDIR 37 Reads the next directory entry. FIOSEEK 7 Sets the current byte offset in a file. FIOSEEK64 53 Sets the current byte offset in a file (64-bit version). FIOUNMOUNT 39 Un-mounts a disk volume. FIOWHERE 8 Returns the current byte position in a file. FIOWHERE64 54 Returns the current byte position in a file (64-bit version). 515 8 VxWorks Kernel Programmer's Guide, 6.6 8.7.4 Version Numbers cdromFsLib has a 4-byte version number. The version number is composed of four parts, from most significant byte to least significant byte: ■ ■ ■ ■ major number minor number patch level build The version number is returned by cdromFsVersionNumGet( ) and displayed by cdromFsVersionNumDisplay( ). 8.8 Read-Only Memory File System: ROMFS ROMFS is a simple, read-only file system that represents and stores files and directories in a linear way (similar to the tar utility). It is installed in RAM with the VxWorks system image at boot time. The name ROMFS stands for Read-Only Memory File System; it does not imply any particular relationship to ROM media. ROMFS provides the ability to bundle VxWorks applications—or any other files for that matter—with the operating system. No local disk or network connection to a remote disk is required for executables or other files. When VxWorks is configured with the ROMFS component, files of any type can be included in the operating system image simply by adding them to a ROMFS directory on the host system, and then rebuilding VxWorks. The build produces a single system image that includes both the VxWorks and the files in the ROMFS directory. When VxWorks is booted with this image, the ROMFS file system and the files it holds are loaded with the kernel itself. ROMFS allows you to deploy files and operating system as a unit. In addition, process-based applications can be coupled with an automated startup facility so that they run automatically at boot time. ROMFS thereby provides the ability to create fully autonomous, multi-process systems. ROMFS can also be used to store applications that are run interactively for diagnostic purposes, or for applications that are started by other applications under specific conditions (errors, and so on). 516 8 Local File Systems 8.8 Read-Only Memory File System: ROMFS 8.8.1 Configuring VxWorks with ROMFS VxWorks must be configured with the INCLUDE_ROMFS component to provide ROMFS facilities. 8.8.2 Building a System With ROMFS and Files Configuring VxWorks with ROMFS and applications involves the following steps: 1. Create a ROMFS directory in the project directory on the host system, using the name /romfs. 2. Copy the application files into the /romfs directory. 3. Rebuild VxWorks. For example, adding a process-based application called myVxApp.vxe from the command line would look like this: cd c:\myInstallDir\vxworks-6.1\target\proj\wrSbc8260_diab mkdir romfs copy c:\allMyVxApps\myVxApp.vxe romfs make TOOL=diab The contents of the romfs directory are automatically built into a ROMFS file system and combined with the VxWorks image. The ROMFS directory does not need to be created in the VxWorks project directory. It can also be created in any location on (or accessible from) the host system, and the make utility’s ROMFS_DIR macro used to identify where it is in the build command. For example: make TOOL=diab ROMFS_DIR="c:\allMyVxApps" Note that any files located in the romfs directory are included in the system image, regardless of whether or not they are application executables. 8.8.3 Accessing Files in ROMFS At run-time, the ROMFS file system is accessed as /romfs. The content of the ROMFS directory can be browsed using the ls and cd shell commands, and accessed programmatically with standard file system routines, such as open( ) and read( ). For example, if the directory installDir/vxworks-6.x/target/proj/wrSbc8260_diab/romfs has been created on the 517 8 VxWorks Kernel Programmer's Guide, 6.6 host, the file foo copied to it, and the system rebuilt and booted; then using cd and ls from the shell (with the command interpreter) looks like this: [vxWorks *]# cd /romfs [vxWorks *]# ls . .. foo [vxWorks *]# And foo can also be accessed at run-time as /romfs/foo by any applications running on the target. 8.8.4 Using ROMFS to Start Applications Automatically ROMFS can be used with various startup mechanisms to start process-based applications automatically when VxWorks boots. See the VxWorks Application Programmer’s Guide: Applications and Processes for more information. 8.9 Target Server File System: TSFS The Target Server File System (TSFS) is designed for development and diagnostic purposes. It is a full-featured VxWorks file system, but the files are actually located on the host system. NOTE: TSFS is not designed for use with large files (whether application executables or other files), and performance may suffer when they are greater than 50 KB. For large files, use FTP or NFS instead of TSFS TSFS provides all of the I/O features of the network driver for remote file access (see 7.8.5 Non-NFS Network Devices, p.400), without requiring any target resources—except those required for communication between the target system and the target server on the host. The TSFS uses a WDB target agent driver to transfer requests from the VxWorks I/O system to the target server. The target server reads the request and executes it using the host file system. When you open a file with TSFS, the file being opened is actually on the host. Subsequent read( ) and write( ) calls on the file descriptor obtained from the open( ) call read from and write to the opened host file. 518 8 Local File Systems 8.9 Target Server File System: TSFS The TSFS VIO driver is oriented toward file I/O rather than toward console operations. TSFS provides all the I/O features that netDrv provides, without requiring any target resource beyond what is already configured to support communication between target and target server. It is possible to access host files randomly without copying the entire file to the target, to load an object module from a virtual file source, and to supply the filename to routines such as ld( ) and copy( ). Each I/O request, including open( ), is synchronous; the calling target task is blocked until the operation is complete. This provides flow control not available in the console VIO implementation. In addition, there is no need for WTX protocol requests to be issued to associate the VIO channel with a particular host file; the information is contained in the name of the file. Consider a read( ) call. The driver transmits the ID of the file (previously established by an open( ) call), the address of the buffer to receive the file data, and the desired length of the read to the target server. The target server responds by issuing the equivalent read( ) call on the host and transfers the data read to the target program. The return value of read( ) and any errno that might arise are also relayed to the target, so that the file appears to be local in every way. For detailed information, see the API reference for wdbTsfsDrv. Socket Support TSFS sockets are operated on in a similar way to other TSFS files, using open( ), close( ), read( ), write( ), and ioctl( ). To open a TSFS socket, use one of the following forms of filename: "TCP:hostIP:port" "TCP:hostname:port" The flags and permissions arguments are ignored. The following examples show how to use these filenames: fd = open("/tgtsvr/TCP:phobos:6164",0,0); /* open socket and connect */ /* to server phobos */ fd = open("/tgtsvr/TCP:150.50.50.50:6164",0,0); /* open socket and /* connect to server /* 150.50.50.50 */ */ */ The result of this open( ) call is to open a TCP socket on the host and connect it to the target server socket at hostname or hostIP awaiting connections on port. The resultant socket is non-blocking. Use read( ) and write( ) to read and write to the TSFS socket. Because the socket is non-blocking, the read( ) call returns 519 8 VxWorks Kernel Programmer's Guide, 6.6 immediately with an error and the appropriate errno if there is no data available to read from the socket. The ioctl( ) usage specific to TSFS sockets is discussed in the API reference for wdbTsfsDrv. This socket configuration allows VxWorks to use the socket facility without requiring sockLib and the networking modules on the target. Error Handling Errors can arise at various points within TSFS and are reported back to the original caller on the target, along with an appropriate error code. The error code returned is the VxWorks errno which most closely matches the error experienced on the host. If a WDB error is encountered, a WDB error message is returned rather than a VxWorks errno. Configuring VxWorks for TSFS Use To use TSFS, configure VxWorks with the INCLUDE_WDB_TSFS component. This creates the /tgtsvr file system on the target. The target server on the host system must also be configured for TSFS. This involves assigning a root directory on your host to TSFS (see the discussion of the target server -R option in Security Considerations, p.520). For example, on a PC host you could set the TSFS root to c:\myTarget\logs. Having done so, opening the file /tgtsvr/logFoo on the target causes c:\myTarget\logs\logFoo to be opened on the host by the target server. A new file descriptor representing that file is returned to the caller on the target. Security Considerations While TSFS has much in common with netDrv, the security considerations are different (also see 7.8.5 Non-NFS Network Devices, p.400). With TSFS, the host file operations are done on behalf of the user that launched the target server. The user name given to the target as a boot parameter has no effect. In fact, none of the boot parameters have any effect on the access privileges of TSFS. In this environment, it is less clear to the user what the privilege restrictions to TSFS actually are, since the user ID and host machine that start the target server may vary from invocation to invocation. By default, any host tool that connects to a target server which is supporting TSFS has access to any file with the same 520 8 Local File Systems 8.9 Target Server File System: TSFS authorizations as the user that started that target server. However, the target server can be locked (with the -L option) to restrict access to the TSFS. The options which have been added to the target server startup routine to control target access to host files using TSFS include: -R Set the root of TSFS. For example, specifying -R /tftpboot prepends this string to all TSFS filenames received by the target server, so that /tgtsvr/etc/passwd maps to /tftpboot/etc/passwd. If -R is not specified, TSFS is not activated and no TSFS requests from the target will succeed. Restarting the target server without specifying -R disables TSFS. 8 -RW Make TSFS read-write. The target server interprets this option to mean that modifying operations (including file create and delete or write) are authorized. If -RW is not specified, the default is read only and no file modifications are allowed. NOTE: For more information about the target server and the TSFS, see the tgtsvr command reference. For information about specifying target server options from Workbench, see the Wind River Workbench User’s Guide: Setting Up Your Hardware and the Wind River Workbench User’s Guide: New Target Server Connections. Using the TSFS to Boot a Target For information about using the TSFS to boot a targets, see 3.11 Booting From the Host File System Using TSFS, p.155. 521 VxWorks Kernel Programmer's Guide, 6.6 522 9 Network File System: NFS 9.1 Introduction 523 9.2 Configuring VxWorks for an NFS Client 524 9.3 Creating an NFS Client 529 9.4 Configuring VxWorks for an NFS Server 535 9.5 Creating an NFS Server 540 9.1 Introduction VxWorks provides an implementation of the Network File System (NFS) application protocol, versions 2 and 3. The first part of this chapter describes how to configure and use an NFS client, which enables a VxWorks target to mount remote file systems and access the contents of those file systems as if they were local. The second part of the chapter describes how to configure and use an NFS server, which enables a VxWorks target to export local systems to remote network systems. NOTE: VxWorks does not normally provide authentication services for NFS requests. If you need the NFS server to authenticate incoming requests, see the nfsdInit( ) and mountdInit( ) reference entries for information on authorization hooks. 523 VxWorks Kernel Programmer's Guide, 6.6 9.2 Configuring VxWorks for an NFS Client The VxWorks supports the following NFS client configuration components, which you can use to include the modules needed to create an NFS client: ■ ■ ■ ■ ■ Core NFS Client NFS Client All NFS v2 Client NFS v3 Client NFS Mount All These components are described in detail below. Core NFS Client The INCLUDE_CORE_NFS_CLIENT component provides nfsCommon, a library that provides core functionality for NFS clients. This library also provides parameters that you can use to specify the NFS user ID, group identifier, and the maximum length of the pathname for a file. This component contains the following configuration parameters: NFS_USER_ID Synopsis: User identifier for NFS access. Default: 2001 NFS_GROUP_ID Synopsis: Group identifier for NFS access. Default: 100 NFS_MAXPATH Synopsis: Maximum file path length. Default: 255 NFS Client All Including the INCLUDE_NFS_CLIENT_ALL component is equivalent to selecting both INCLUDE_NFS2_CLIENT and INCLUDE_NFS3_CLIENT, the components that pull in client support for NFS version 2 and NFS version 3 respectively. 524 9 Network File System: NFS 9.2 Configuring VxWorks for an NFS Client This component requires the INCLUDE_NFS2_CLIENT and INCLUDE_NFS3_CLIENT components. NFS v2 Client The INCLUDE_NFS2_CLIENT component provides nfs2Lib and nfs2Drv, which provide support of an NFS version two client. Using this client, you can mount exported NFS (version two) directories to your VxWorks target. This component requires the INCLUDE_CORE_NFS_CLIENT component. Initialization This component also configures the VxWorks image to initialize the NFS v2 client, which includes a call to nfsAuthUnixSet( ): nfsAuthUnixSet ( sysBootParams.hostName, NFS_USER_ID, NFS_GROUP_ID, 0, (int *) 0); Values for the NFS_USER_ID and NFS_GROUP_ID parameters are taken from the required INCLUDE_CORE_NFS_CLIENT component. Parameters This component contains the following configuration parameters: NFS2_CLIENT_CACHE_DEFAULT_NUM_LINES Synopsis: Default number of cache lines. Default: 16 The NFS client implementation uses a persistent cache, which is structured as a multi-line buffer cache. This parameter configures the default number of lines in the NFS v2 client cache. The value can be decreased to as low as 1, or increased. You can modify the number of cache lines, either at build time or at run-time. To configure the cache at run time, call the routine usrNfs2CacheInit( ): usrNfs2CacheInit (UINT32 numLines, UINT32 lineSize, UINT32 options); NFS2_CLIENT_CACHE_DEFAULT_LINE_SIZE Synopsis: Default number of bytes in cache line. Default: 16384 525 9 VxWorks Kernel Programmer's Guide, 6.6 The NFS client implementation uses a persistent cache, which is structured as a multi-line buffer cache. The cache line size must be a power of two. This parameter configures the default size of the NFS v2 client cache line. The default value for this is 16384 (16 kB). When combined with the default number of cache lines, this yields a default cache size of 256 kB. You can modify the number of cache line size, either at build time or at run-time. To configure the cache at run time, call the routine usrNfs2CacheInit( ): usrNfs2CacheInit (UINT32 numLines, UINT32 lineSize, UINT32 options); Changing the size of the cache will not affect any existing cache. It will only impact future caches. NFS2_CLIENT_CACHE_DEFAULT_OPTIONS Synopsis: Default cache options. Default: 0 This parameter configures the default options for the NFS v2 client cache. The two valid settings for this parameter are: 0 The default value of zero (0) means that the cache will collect the written data and only send it to the server when the cache line is full, or it needs to be flushed (no options), which is the default value 1, NFS_CACHE_WRITE_THROUGH A value of one means that the cache will be write-through. You can modify the cache options, either at build time or at run-time. To configure the cache at run time, call the routine usrNfs2CacheInit( ): usrNfs2CacheInit (UINT32 numLines, UINT32 lineSize, UINT32 options); NFS v3 Client The INCLUDE_NFS3_CLIENT component provides the nfs3Lib and nfs3Drv libraries, which provide support of an NFS version three client. Using this client, you can mount exported NFS (version three) directories to your VxWorks target. This component requires the INCLUDE_CORE_NFS_CLIENT component. 526 9 Network File System: NFS 9.2 Configuring VxWorks for an NFS Client Initialization This component also configures the VxWorks image to initialize the NFS v3 client, which includes a call to nfsAuthUnixSet( ): nfsAuthUnixSet ( sysBootParams.hostName, NFS_USER_ID, NFS_GROUP_ID, 0, (int *) 0); Values for the NFS_USER_ID and NFS_GROUP_ID parameters to this routine are taken from the required INCLUDE_CORE_NFS_CLIENT component. Parameters This component contains the following configuration parameters: NFS3_CLIENT_CACHE_DEFAULT_NUM_LINES 9 Synopsis: Default number of cache lines. Default: 16 The NFS client implementation uses a persistent cache, which is structured as a multi-line buffer cache. This parameter configures the default number of lines in the NFS v3 client cache. The value can be decreased to as low as 1, or increased. You can modify the number of cache lines, either at build time or at run-time. To configure the cache at run time, call the routine usrNfs3CacheInit( ): usrNfs3CacheInit (UINT32 numLines, UINT32 lineSize, UINT32 options); NFS3_CLIENT_CACHE_DEFAULT_LINE_SIZE Synopsis: Default number of bytes in cache line. Default: 16384 The NFS client implementation uses a persistent cache, which is structured as a multi-line buffer cache. The cache line size must be a power of two. This parameter configures the default size of the NFS v3 client cache line. The default value for this is 16384 (16 kB). When combined with the default number of cache lines, this yields a default cache size of 256 kB. You can modify the number of cache line size, either at build time or at run-time. To configure the cache at run time, call the routine usrNfs3CacheInit( ): usrNfs3CacheInit (UINT32 numLines, UINT32 lineSize, UINT32 options); 527 VxWorks Kernel Programmer's Guide, 6.6 Changing the size of the cache will not affect any existing cache. It will only impact future caches. NFS3_CLIENT_CACHE_DEFAULT_OPTIONS Synopsis: Default cache options. Default: 0 This parameter configures the default options for the NFS v3 client cache. The two valid settings for this parameter are: 0 The default value of zero (0) means that the cache will collect the written data and only send it to the server when the cache line is full, or it needs to be flushed (no options), which is the default value 1, NFS_CACHE_WRITE_THROUGH A value of one means that the cache will be write-through. You can modify the cache options, either at build time or at run-time. To configure the cache at run time, call the routine usrNfs3CacheInit( ): usrNfs3CacheInit (UINT32 numLines, UINT32 lineSize, UINT32 options); Configuring NFS3 Client Writes The NFS v3 client has one additional configurable parameter that is not available on NFS v2. According to the RFC, the NFS v3 client can dictate to an NFS v3 server how it should perform the write operations. At runtime, the NFS v3 client can be set to inform the server that it should perform writes one of the following styles: ■ ■ ■ UNSTABLE FILE_SYNC DATA_SYNC The default setting is UNSTABLE. You can use two routines to configure these options at run-time: ■ ■ nfs3StableWriteSet(stable_how mode) lets you set the mode nfs3StableWriteGet( ) routine gets the current mode NOTE: This option does not exist in NFS v2. 528 9 Network File System: NFS 9.3 Creating an NFS Client NFS Mount All The INCLUDE_NFS_MOUNT_ALL component configures a VxWorks target to make a boot-time call to nfsMountAll( ). This routine automatically mounts all file systems exported by the boot host system. This component requires the INCLUDE_NFS_CLIENT_ALL component. This component contains the following configuration parameter: GROUP_EXPORTS Synopsis: Remove check for GroupName during MountAll. Default: FALSE An NFS server can specify that an exported file system is intended for particular group of clients. Before mounting an exported file system, a client typically checks that it is a group member. If the client is not a group member, it does not mount the file system. To configure the client to skip this check, set this parameter to TRUE. The default of FALSE ensures that the check occurs. 9.3 Creating an NFS Client To create an NFS client and use it to access a remote networked file system: 1. Call nfs2Drv( ) or nfs3Drv( ) to initialize support for NFS v2 or v3 or both. Normally, you should not need to call either of these routines explicitly. VxWorks calls these routines automatically at boot time if the image includes INCLUDE_NFS_CLIENT_ALL. For NFS v2 only, use INCLUDE_NFS2_CLIENT. To initialize NFS v3 only, use INCLUDE_NFS3_CLIENT. 2. Call nfsAuthUnixSet( ) to configure the user name and user ID the device should use when communicating with a particular host. VxWorks calls nfsAuthUnixSet( ) automatically at boot time if the image contains INCLUDE_NFS_CLIENT_ALL, INCLUDE_NFS2_CLIENT, or INCLUDE_NFS3_CLIENT. The values for user name and user ID are supplied by the parameters to INCLUDE_CORE_NFS_CLIENT. 3. Call hostAdd( ) to configure the host table to know of the host system from which you want to mount an exported file system. 529 9 VxWorks Kernel Programmer's Guide, 6.6 VxWorks calls hostAdd( ) for the host system automatically at boot time. If you want to mount file systems from other remote systems, you need to make and explicit hostAdd( ) call for those systems. 4. Call nfsMount( ) or nfsMountAll( ) to actually mount a remote file system. The nfsMountAll( ) routine queries the specified remote system for a list of exported file names and then creates NFS client device instances for each exported file system. To unmount a file system, use nfsUnmount( ). Use nfsDevShow( ) to display a list of the mounted NFS devices. As a convenience, the INCLUDE_NFS_MOUNT_ALL component configures an image to make a boot time call to nfsMountAll( ) to mount all file systems exported by the boot host. The following sections supplement and expand on the procedure outlined above. Exporting File Systems from the Remote NFS Server For a UNIX NFS server, the /etc/exports file specifies which of the server’s file systems are exported for mounting by remote NFS clients. If a file system on a UNIX NFS server is not listed in /etc/exports, the file system is not exported, which means other machines cannot use NFS to mount it. For example, consider an /etc/exports file that contains the line: /usr The server exports /usr without restriction. If you want to limit access to this directory, you can include additional parameters on the line. For example: 1. On the UNIX box, login as root (super user). 2. Edit: /etc/exports 3. Specify the path and permission for the file system that you would export. For example: /usr * (rw) For more information on these parameters, consult your UNIX system documentation. 4. Export the file system, run: exportfs -ra 5. On the UNIX target, run the NFS daemon: rpc.nfsd 6. Run: rpc.rquotad 7. To run mount the daemon, run: rpc.mountd To check whether NFS is running, use: rpcinfo -p. 530 9 Network File System: NFS 9.3 Creating an NFS Client Windows systems also support NFS. Thus, it is possible to configure a directory on a Windows system so that it is exported over NFS. The exact procedures for doing so depend upon the particular network package you purchased. For more information, consult the documentation included with your Windows networking package. Setting Your NFS Client Name, User ID, and Group ID Internally, NFS depends upon RPC to handle the remote execution of the commands (open, read, write, and others) that access the data in the remote file system. Associated with the RPC protocol is an authentication system known as AUTH_UNIX. This authentication system requires RPC peers to provide a user name, a user ID, and a group name. The recipient of an RPC message uses this information to decide whether to honor or ignore the RPC request. On a VxWorks host, you can set the NFS user name, user ID, and group name using the NFS_GROUP_ID and NFS_USER_ID parameters included in the INCLUDE_CORE_NFS_CLIENT component. You can also set these values by calling nfsAuthUnixSet( ) or nfsAuthUnixPrompt( ). For example, to use nfsAuthUnixSet( ) to set the NFS user ID to 1000 and the NFS group ID to 200 for the machine mars, you would call nfsAuthUnixSet( ) as follows: -> nfsAuthUnixSet "mars", 1000, 200, 0 The nfsAuthUnixPrompt( ) routine provides a more interactive way of setting the NFS authentication parameters from the shell. On UNIX systems, a user ID is specified in the file /etc/passwd. A list of groups that a user belongs to is specified in the file /etc/group. To configure a default user ID and group ID, set NFS_USER_ID and NFS_GROUP_ID. The NFS authentication parameters will take on these values at system startup. If NFS file access is unsuccessful, make sure that the configuration is correct. Mounting a Remote File System After setting your NFS client name, user ID, and group ID, you are ready to call nfsMount( ) to mount any file system exported by a known host. To add a system to the list of hosts known to a VxWorks system, call hostAdd( ): hostAdd ("host", "IPaddress" ) This routine associates a host name with an IP address. Thus, if you wanted to mount a file system exported by a system called mars, you would need to have 531 9 VxWorks Kernel Programmer's Guide, 6.6 already called hostAdd( ) for mars. For example, if mars were at 192.168.10.1 you would need to call hostAdd( ) as follows: hostAdd ("mars", "192.168.10.1" ) If mars exports a file system called /usr, you can now use a call to nfsMount( ) to create a local mount of that remotely exported file system. The syntax of an nfsMount( ) call is as follows: nfsMount ("hostName", "hostFileSys", "localName") hostName The host name of the NFS server that exports the file system you want to mount. hostFileSys The name of the host file system or subdirectory as it is known on the exporting NFS server system. localName The local name to assign to the file system. For example, if you wanted to mount a remote file system, /d0/, on your target, wrs, as a device called /myDevice0/, you would make the following call to nfsMount( ): nfsMount ("wrs", "/d0/", "/myDevice0/"); The VxWorks target now has access to the contents of /d0/, although using the device name, /myDevice0/. For example, if the remote device stores the file, /d0/bigdog, you can access this file from the wrs target using the pathname, /myDevice0/bigdog. If you want the local device to use the same device name as is used on the exporting system, use a NULL as the third parameter of the nfsMount( ) call. For example: nfsMount ("wrs", "/d0/", NULL); Or, from the kernel shell: -> nfsMount "wrs", "/d0/" On the VxWorks target, the nfsMount( ) call creates the local device, /d0/. Thus, on the target, the pathname to bigdog is the same as on the exporting system; that is: /d0/bigdog. If you do not need to mount the remote file system under a new name, you should consider using nfsMountAll( ) instead of nfsMount( ). A call to nfsMountAll( ) mounts all file systems that are exported from the remote system and that are accessible to the specified client. 532 9 Network File System: NFS 9.3 Creating an NFS Client The syntax of nfsMountAll( ) is as follows: nfsMountAll( "hostName", "clientName", quietFlag ) hostName The name of the host from which you want to mount all exported file systems. clientName The name of a client specified in an access list, if any. A NULL clientName mounts only those file systems that are accessible to any client. quietFlag A boolean value that tells nfsMountAll( ) whether to execute in verbose or silent mode. FALSE indicates verbose mode, and TRUE indicates quiet mode. 533 9 VxWorks Kernel Programmer's Guide, 6.6 Using ioctl( ) With Open Files from a Mounted Directory After opening a file in a mounted directory, you can work with the file using the ioctl( ) control functions listed in Table 9-1. Table 9-1 Supported I/O Control Functions for Files Accessed through NFS IOCTL Description FIOGETNAME Gets the file name of fd and copies it to the buffer referenced by nameBuf: status = ioctl (fd, FIOGETNAME, &nameBuf); FIONREAD Copies to nBytesUnread the number of bytes remaining in the file specified by fd: status = ioctl (fd, FIONREAD, &nBytesUnread); FIOSEEK Sets the current byte offset in the file to the position specified by newOffset. If the seek goes beyond the end-of-file, the file grows. The end-of-file pointer gets moved to the new position, and the new space is filled with zeros: status = ioctl (fd, FIOSEEK, newOffset); FIOSYNC Flush data to the remote NFS file. It takes no additional argument: status = ioctl (fd, FIOSYNC, 0); FIOWHERE Returns the current byte position in the file. This is the byte offset of the next byte to be read or written. It takes no additional argument: position = ioctl (fd, FIOWHERE, 0); FIOREADDIR Reads the next directory entry. Use the third argument in the ioctl( ) call to supply a pointer to a directory descriptor of type DIR. DIR dirStruct; fd = open ("directory", O_RDONLY); status = ioctl (fd, FIOREADDIR, &dirStruct); Normally, you do not use the FIOREADDIR functionality directly. Instead, you would call readdir( ). See the reference entry for dirLib. 534 9 Network File System: NFS 9.4 Configuring VxWorks for an NFS Server Table 9-1 Supported I/O Control Functions for Files Accessed through NFS (cont’d) IOCTL Description FIOFSTATGET Gets file status information (directory entry data). Use the third argument in the ioctl( ) call to supply a pointer to a stat structure that is filled with data describing the specified file. For example: struct stat statStruct; fd = open ("file", O_RDONLY); status = ioctl (fd, FIOFSTATGET, &statStruct); Normally, you do not use the FIOFSTATGET functionality directly. Instead, you would stat( ) or fstat( ) routines get file information. See the manual entry for dirLib. FIOFSTATFSGET Gets the file system parameters for and open file descriptor. Use the third argument in the ioctl( ) call to supply a pointer to a statfs structure that is filled with data describing the underlying file system. statfs statfsStruct; fd = open ("directory", O_RDONLY); status = ioctl (fd, FIOFSTATFSGET, &statfsStruct); Normally, you do not use the FIOFSTATFSGET functionality directly. Instead, you would stat( ) or fstat( ) routines get file information. See the manual entry for dirLib. 9.4 Configuring VxWorks for an NFS Server VxWorks supports the following NFS server configuration components, which you can use to include the modules needed to create an NFS server: ■ ■ ■ ■ NFS Server NFS server All NFS server V2 NFS server V3 These components are discussed in detail below. 535 9 VxWorks Kernel Programmer's Guide, 6.6 NFS Server The INCLUDE_CORE_NFS_SERVER component provides nfsd, the library that supplies the NFS server daemon initialization routines. For more information on these routines, see the nfsd reference entry. This component also supplies configuration parameters that set basic configuration values for the server. NOTE: The NFS server maintains a reply cache of up to 64 recently transmitted reply messages. The purpose of this cache is to deal with RPC retransmissions. If the XID of an incoming NFS request matches that of a previously replied message, the cached reply is sent back instead of actually executing the NFS request. Each entry in the server reply cache requires 8800 bytes for the entry itself and 48 bytes for each cache node. Thus, if there were three entries in the cache, the memory usage would be 26,544 bytes, which is (3 * 8800) + (3 * 48) bytes. If there were the full 64 entries in the cache, the memory usage would be 566,272 bytes. If you think you have noticed a memory leak in NFS, please consider whether this memory use accounts for the discrepancy. This component contains the following configuration parameters: NFS_MAXPATH Synopsis: Maximum length of a file path string (excludes file name). Default: 255 NFS_USER_ID Synopsis: User identifier for NFS access. Default: 2001 NFS_MAXFILENAME Synopsis: Maximum file name length. Valid values range from 1 to 99. Default: 40 This parameter specifies the maximum length of a filename. If a filename is longer than this value then it is truncated before returning it to the client. This parameter should be set carefully since it affects the amount of memory allocated by the server. 536 9 Network File System: NFS 9.4 Configuring VxWorks for an NFS Server NFS_GROUP_ID Synopsis: Group identifier for NFS access. Default: 100 NFS server All Including the INCLUDE_NFS_SERVER_ALL component is equivalent to selecting both INCLUDE_NFS3_SERVER and INCLUDE_NFS2_SERVER. This component requires the INCLUDE_NFS3_SERVER, INCLUDE_NFS2_SERVER, and INCLUDE_NFS_SERVER_INSTALL components. 9 NFS server V2 The INCLUDE_NFS2_SERVER component provides nfs2dLib and mount1Lib. The nfs2dLib library implements the NFS version 2 procedures as specified in the Network File System Protocol Specification (RFC 1094). The mount1Lib library implements a mount version one server to support mounting VxWorks file systems remotely. The mount server is an implementation of version 1 of the mount protocol as defined in RFC 1094. The INCLUDE_NFS2_SERVER component requires the INCLUDE_CORE_NFS_SERVER and INCLUDE_NFS_SERVER_INSTALL components. NOTE: VxWorks does not normally provide authentication services for NFS requests. If you need to authenticate incoming requests, see the documentation for nfsdInit( ) and mountdInit( ) for information about authorization hooks. To actually export a file system, you must call nfsExport( ). Table 9-2 lists the requests that RFC 1813 accepted from clients. For details of their use, see RFC 1094, NFS: Network File System Protocol Specification. NFS server V3 The INCLUDE_NFS3_SERVER component provides nfs3dLib and mount3Lib. The nfs3dLib library provides an implementation of the NFS version 3 procedures as specified in the RFC 1813 (Network File System Protocol Specification). The 537 VxWorks Kernel Programmer's Guide, 6.6 mount3Lib library implements a mount server. The mount server is an implementation of version 3 mount protocol as defined in RFC 1813. NFS version 3 requires mount versions 1 and 3. Also required are INCLUDE_CORE_NFS_SERVER and INCLUDE_NFS_SERVER_INSTALL. To actually export a file system, you must call nfsExport( ). The INCLUDE_NFS3_SERVER component requires the INCLUDE_CORE_NFS_SERVER and INCLUDE_NFS_SERVER_INSTALL components. NOTE: VxWorks does not normally provide authentication services for NFS requests. If you need to authenticate incoming requests, see the documentation for nfsdInit( ) and mountdInit( ) for information about authorization hooks. The following requests are accepted from clients. For details of their use, see RFC 1813: NFS: Network File System Protocol Specification. Table 9-2 RFC 1813 Supported Client Requests Procedure Name Procedure Number NFSPROC_NULL 0 NFSPROC_GETATTR 1 NFSPROC_SETATTR 2 NFSPROC_LOOKUP 3 NFSPROC_ACCESS 4 NFSPROC_READLINK 5 – not supported, limitation in DOSFS NFSPROC_READ 6 NFSPROC_WRITE 7 NFSPROC_CREATE 8 NFSPROC_MKDIR 9 NFSPROC_SYMLINK 10 – not supported NFSPROC_MKNOD 11 – not supported NFSPROC_REMOVE 12 538 9 Network File System: NFS 9.4 Configuring VxWorks for an NFS Server Table 9-2 RFC 1813 Supported Client Requests (cont’d) Procedure Name Procedure Number NFSPROC_RMDIR 13 NFSPROC_RENAME 14 NFSPROC_LINK 15 – not supported NFSPROC_READDIR 16 NFSPROC_READDIRPLUS 17 NFSPROC_FSSTAT 18 NFSPROC_FSINFO 19 NFSPROC_PATHCONF 20 NFSPROC_COMMIT 21 9 539 VxWorks Kernel Programmer's Guide, 6.6 9.5 Creating an NFS Server To set up an NFS file server on a VxWorks target, you need to configure the VxWorks target to include the appropriate NFS server configuration components, described in 9.4 Configuring VxWorks for an NFS Server, p.535. You also need a file system for export; for information about file systems, see 8. Local File Systems. After you have a file system to export, call nfsExport( ) to export the specified file system. Initializing an NFS File System for Export The following code fragment creates a RAM drive, initializes it for dosFs, and exports the file system for NFS clients on the network: unsigned myBlockSize; /* block size in bytes */ unsigned myTotalSize; /* disk size in bytes */ myBlockSize = 512; myTotalSize = 16777216; /* 16Mb */ xbdRamDiskDevCreate (myBlockSize, myTotalSize, FALSE, "/ramDrv"); dosFsVolFormat ("/ramDrv", 2, 0); nfsExport ("/ramDrv", 0, FALSE, 0); ! CAUTION: For NFS-exportable file systems, the device name absolutely must not end in a slash. Exporting a File System through NFS After you have an exportable file system, call nfsExport( ) to make it available to NFS clients on your network. Then mount the file system from the remote NFS client using the facilities of that system. The following example shows how to export the new file system from a VxWorks target called vxTarget, and how to mount it from a typical UNIX system. 1. After the file system (/export in this example) is initialized, the following routine call specifies it as a file system to be exported with NFS: nfsExport ("/export", 0, FALSE, 0); The first three arguments specify the name of the file system to export; the VxWorks NFS export ID (0 means to assign one automatically); and whether 540 9 Network File System: NFS 9.5 Creating an NFS Server to export the file system as read-only. The last argument is a placeholder for future extensions. 2. ! To mount the file system from another machine, see the system documentation for that machine. Specify the name of the VxWorks system that exports the file system, and the name of the desired file system. You can also specify a different name for the file system as seen on the NFS client. CAUTION: On UNIX systems, you normally need root access to mount file systems. For example, on a typical UNIX system, the following command (executed with root privilege) mounts the /export file system from the VxWorks system vxTarget, using the name /mnt for it on UNIX: 9 -> /etc/mount vxTarget:/export /mnt 541 VxWorks Kernel Programmer's Guide, 6.6 542 10 Flash File System Support: TrueFFS 10.1 Introduction 543 10.2 Overview of Implementation Steps 545 10.3 Creating a System with TrueFFS 546 10.4 Using TrueFFS Shell Commands 558 10.5 Using TrueFFS With HRFS 560 10.1 Introduction TrueFFS is a flash management facility that provides access to flash memory by emulating disk access. It provides VxWorks with block device functionality, which allows either the dosFs file system (with or without TRFS support) or the HRFS file system to be used to access flash memory in the same manner as a disk. For information about the file system facilities, see 8.5 MS-DOS-Compatible File System: dosFs, p.478), 7.8.9 Transaction-Based Reliable File System Facility: TRFS, p.405, and 8.4 Highly Reliable File System: HRFS, p.459. In addition, TrueFFS provides full flash media management capabilities. TrueFFS is a VxWorks-compatible implementation of M-Systems FLite, version 2.0. This system is reentrant, thread-safe, and supported on all CPU architectures that host VxWorks. TrueFFS consists of the following four layers: 543 VxWorks Kernel Programmer's Guide, 6.6 ■ The core layer, which connects the other layers and handles global facilities, such as back-grounding, garbage collection, timers, and other system resources. This layer provides the block device interface for a file system. ■ The flash translation layer, which maintains the block allocation map that associates the file system’s view of the storage medium with erase blocks in flash. ■ The Memory Technology Device (MTD) layer, which implements the low-level programming of the flash medium (map, read, write, and erase functions). ■ The socket layer, which provides an interface between TrueFFS and the board hardware with board-specific hardware access routines. Figure 10-1 illustrates the relationship between the file system, TrueFFS layers, and the flash medium itself. Figure 10-1 File System, TrueFFS Layers, and Flash File System Core Layer TrueFFS Translation Layer MTDs Socket Layer Flash Memory This chapter provides instructions for using TrueFFS with the MTDs and drivers that are included in this release. It provides quick-start material for configuring TrueFFS and formatting TrueFFS drives, and thus presents the basic steps required to use the default TrueFFS facilities with your application. It also provides information about creating a boot image region that excludes TrueFFS, and about writing the boot image to that region. If you must customize or create new socket drivers or MTDs, or would simply like more detailed information about TrueFFS technology, see the VxWorks Device Driver Developer’s Guide: Flash File System Support with TrueFFS. 544 10 Flash File System Support: TrueFFS 10.2 Overview of Implementation Steps NOTE: This version of the TrueFFS product is a block device driver to VxWorks that, although intended to be file system neutral, is provided for use with the dosFs file system or the HRFS file system. The configuration steps for using TrueFFS with dosFs and HRFS are slightly different. 10.2 Overview of Implementation Steps This section provides an overview of how to use TrueFFS with VxWorks BSPs that provide support for the TrueFFS component. To determine if your BSP provides TrueFFS support, see the online BSP reference documentation (or the file installDir/vxworks-6.x/target/config/bspName/target.ref). You may need to write certain sub-components for your application. This is most often required for the MTD layer. See the VxWorks Device Driver Developer’s Guide: Flash File System Support with TrueFFS for information in this regard. To determine if this release provides an MTD suitable for your flash hardware, see 10.3.1 Selecting an MTD, p.546 and Including the MTD Component, p.550. Step 1: Select an MTD Component Choose an MTD, appropriate for your hardware, from those provided with the TrueFFS product. See 10.3.1 Selecting an MTD, p.546. Step 2: Identify the Socket Driver Ensure that you have a working socket driver. The socket driver is a source code component, implemented in the file sysTffs.c. For BSPs that already support TrueFFS, the socket driver is fully defined and located in the BSP directory. See 10.3.2 Identifying the Socket Driver, p.547. Step 3: Configure the System Configure your system for TrueFFS by adding the appropriate VxWorks components. Minimum support requires components for a file system and the four TrueFFS layers. See 10.3.3 Configuring VxWorks with TrueFFS, p.548. 545 10 VxWorks Kernel Programmer's Guide, 6.6 Step 4: Build the System Build the system from Workbench or from the command line with the vxprj facility. See 10.3.4 Building the System, p.551. Step 5: Boot the Target and Format the Drives Boot the target and then format the drives. See 10.3.5 Formatting the Flash, p.552. Step 6: Create a Flash Region for Boot Code Optionally, create a boot image region that excludes TrueFFS, and write the boot image to that region (this region can alternatively be used for a system startup log or configuration data). See 10.3.6 Reserving a Region in Flash for a Boot Image, p.554. Step 7: Mount the Drive Mount the file system on a TrueFFS flash drive. See 10.3.7 Mounting the Drive, p.556. Step 8: Test the Drive Test your drive(s). See 10.3.8 Testing the Drive, p.557. 10.3 Creating a System with TrueFFS This section provides detailed instructions on configuring VxWorks with the required TrueFFS and file system components, building the system, formatting the flash, mounting the drive, and testing the drive. It also provides information about creating a region for a boot image. 10.3.1 Selecting an MTD Determine whether any of the MTDs provided with this release support the device that you intend to use for TrueFFS. Devices are usually identified by their JEDEC IDs. If you find an MTD appropriate to your flash device, you can use that MTD. These drivers are also provided in binary form; so you do not need to compile the MTD source code unless you have modified it. 546 10 Flash File System Support: TrueFFS 10.3 Creating a System with TrueFFS The directory installDir/vxworks-6.x/target/src/drv/tffs contains the source code for the following types of MTD components: ■ MTDs that work with several of the devices provided by Intel, AMD, Fujitsu, and Sharp. ■ Two generic MTDs that can be used for devices complying with CFI. To better support the out-of-box experience, these MTDs attempt to cover the widest possible range of devices (in their class) and of bus architectures. Consequently, the drivers may not provide the performance you may need for the run-time environment that you want to target. Also note that your hardware configuration may require some changes to the generic drivers in order to work. Consider such requirements as word or byte access limitations, or unusual array configurations. If the performance and size of the drivers provided do not match your requirements, you can modify them to better suit your needs. For more information, see the VxWorks Device Driver Developer’s Guide: Flash File System Support with TrueFFS. NOTE: For the list of the MTD components and details about adding the MTD component to your system, see Including the MTD Component, p.550. 10.3.2 Identifying the Socket Driver The socket driver that you include in your system must be appropriate for your BSP. Some BSPs include socket drivers, others do not. The socket driver file is sysTffs.c and, if provided, it is located in your BSP directory. If your BSP does not provide this file, follow the procedure described in the VxWorks Device Driver Developer’s Guide: Flash File System Support with TrueFFS, which explains how to port a stub version to your hardware. In either case, the build process requires that a working socket driver (sysTffs.c) be located in the BSP directory. For more information, see Adding the Socket Driver, p.551. 547 10 VxWorks Kernel Programmer's Guide, 6.6 10.3.3 Configuring VxWorks with TrueFFS To configure a VxWorks systems with TrueFFS, you must include: ■ Components to fully support either the dosFs or HRFS file system. ■ The INCLUDE_XBD_BLKDEV component (see XBD Block Device Wrapper, p.404). ■ The core layer TrueFFS component, INCLUDE_TFFS. Some BSPs—like the PowerQuiccII— have a custom MTD in sysTffs.c and do not need any additional selections. For this BSP you must identify the flash in which TrueFFS will reside (INCLUDE_SIMM_TFFS). ■ At least one software module from each of the other three TrueFFS layers (translation, MTD, and socket). You can configure and build your system either from the command line or with Workbench. For general information on configuration procedures, see the Wind River Workbench User’s Guide and the VxWorks Command-Line Tools User’s Guide. For either configuration and build method, special consideration must be given to cases in which either the socket driver or the MTD, or both, are not provided. The drivers must be registered and MTDs need appropriate component descriptions. For more information, see the VxWorks Device Driver Developer’s Guide: Flash File System Support with TrueFFS. For supported BSPs this is usually taken care of automatically by including components. It is more of a concern when adding TrueFFS support to a BSP. NOTE: Included with TrueFFS are sources for several MTDs and socket drivers. The MTDs are in installDir/vxworks-6.x/target/src/drv/tffs. The socket drivers are defined in the sysTffs.c files provided in the installDir/vxworks-6.x/target/config/bspname directory for each BSP that supports TrueFFS. Including File System Components File system support—for either dosFs or HRFS—must be included in your system for TrueFFS to be useful. For information about these file systems and components upon which they depend, see 8.5 MS-DOS-Compatible File System: dosFs, p.478 and 8.4 Highly Reliable File System: HRFS, p.459. 548 10 Flash File System Support: TrueFFS 10.3 Creating a System with TrueFFS There are other file system components that are not required, but which may be useful. These components add support for the basic functionality needed to use a file system, such as the commands ls, cd, copy, and so forth (which are provided by the INCLUDE_DISK_UTIL component). Including the XBD Wrapper Component VxWorks must be configured with the INCLUDE_XBD_BLKDEV component for the TrueFFS block device driver (which is not XBD-compatible). For more information, see XBD Block Device Wrapper, p.404). Including the Core TrueFFS Component 10 VxWorks must be configured with the TrueFFS core component, INCLUDE_TFFS. Including this component triggers the correct sequence of events, at boot time, for initializing this product. It also ensures that the socket driver is included in your system (see Adding the Socket Driver, p.551). Including Utility Components TrueFFS provides optional utility components for automatic drive detection, show routines, and writing a boot image to flash. INCLUDE_TFFS_MOUNT Including this component adds automatic detection (on booting) of existing formatted TrueFFS drives. INCLUDE_TFFS_SHOW Including this component adds two TrueFFS configuration display utilities, tffsShow( ) and tffsShowAll( ) for use from the shell. The tffsShow( ) routine prints device information for a specified socket interface. It is particularly useful when trying to determine the number of erase units required to write a boot image (10.3.6 Reserving a Region in Flash for a Boot Image, p.554). The tffsShowAll( ) routine provides the same information for all socket interfaces registered with VxWorks. The tffsShowAll( ) routine can be used from the shell to list the drives in the system. The drives are listed in the order in which they were registered. This component is not included by default. 549 VxWorks Kernel Programmer's Guide, 6.6 INCLUDE_TFFS_BOOT_IMAGE Including this component provides the tffsBootImagePut( ) routine (in sysTffs.o). The routine is used to write a boot image to flash memory (see Writing the Boot Image to Flash, p.556) NOTE: INCLUDE_TFFS_BOOT_IMAGE is included by default for some BSPs. Including the MTD Component Add the MTD component appropriate to your flash device (10.3.1 Selecting an MTD, p.546) to your system. The MTD components for flash devices from Intel, AMD, Fujitsu, and Sharp, are described in Table 10-1. For more information about support for these devices, see the VxWorks Device Driver Developer’s Guide: Flash File System Support with TrueFFS. Table 10-1 Components for TrueFFS MTDs Component Device INCLUDE_MTD_CFISCS CFI/SCS device. INCLUDE_MTD_CFIAMD CFI-compliant AMD and Fujitsu devices. INCLUDE_MTD_I28F016 Intel 28f016 device. INCLUDE_MTD_I28F008 Intel 28f008 device. INCLUDE_MTD_AMD AMD, Fujitsu: 29F0{40,80,16} 8-bit devices. If you have written your own MTD, you must be sure that it is correctly defined for inclusion in the system, and that it explicitly requires the transition layer. See the VxWorks Device Driver Developer’s Guide: Flash File System Support with TrueFFS for information. Including the Translation Layer Component Choose the translation layer appropriate to the technology used by your flash medium. The main variants of flash devices are NOR and NAND. TrueFFS provides support for: ■ 550 NOR devices. 10 Flash File System Support: TrueFFS 10.3 Creating a System with TrueFFS ■ NAND devices that conform to the SSFDC specification. The translation layer is provided in binary form only. The translation layer components are listed in Table 10-2. Table 10-2 Components for TrueFFS Translation Layers Component Description INCLUDE_TL_FTL The translation layer for NOR flash devices. If you can execute code in flash, your device uses NOR logic. INCLUDE_TL_SSFDC The translation layer for devices that conform to Toshiba Solid State Floppy Disk Controller Specifications. TrueFFS supports only those NAND devices that comply with the SSFDC specification. The component descriptor files specify the dependency between the translation layers and the MTDs; therefore, when configuring through Workbench or the command-line vxprj facility, you do not need to explicitly select a translation layer. The build process handles it for you. For more information about the translation layer, see the VxWorks Device Driver Developer’s Guide: Flash File System Support with TrueFFS. Adding the Socket Driver Inclusion of the socket driver is automatic for BSPs that provide the driver. By including the core TrueFFS component, INCLUDE_TFFS, in VxWorks, the build process checks for a socket driver, sysTffs.c, in the BSP directory and includes that file in the system. If your BSP does not provide a socket driver, follow the procedure described in the VxWorks Device Driver Developer’s Guide: Flash File System Support with TrueFFS for writing a socket driver. To include the socket driver in your system, a working version of the socket driver (sysTffs.c) must be located in you BSP directory. 10.3.4 Building the System Build the system from Workbench or from the command line with vxprj. 551 10 VxWorks Kernel Programmer's Guide, 6.6 10.3.5 Formatting the Flash ! WARNING: If the flash array for your system is used for a boot image (a boot loader or self-booting VxWorks system) as well as file system media, space must be reserved for the boot image before you format the flash for TrueFFS. For more information, see 10.3.6 Reserving a Region in Flash for a Boot Image, p.554. First, boot your system. After the system boots and registers the socket driver(s), start the shell. From the shell, run tffsDevFormat( ) or sysTffsFormat( ) to format the flash memory for use with TrueFFS—use the latter if the BSP provides it (sysTffsFormat( ) performs some setup operations and then calls tffsDevFormat( )). For example, the tffsDevFormat( ) routine takes two arguments, a drive number and a format argument: tffsDevFormat (int tffsDriveNo, int formatArg); NOTE: You can format the flash medium even if though block device driver has not yet been associated with the flash. NOTE: The size of the flash media available for use is reduced by one sector for TrueFFS internal use. Specifying the Drive Number The first argument for tffsDevFormat( ), tffsDriveNo, is the drive number (socket driver number), which identifies the flash medium to be formatted. Most systems have a single flash drive, but TrueFFS supports up to five. The socket registration process determines the drive number. Drive numbers are assigned to the flash devices on the basis of the order in which the socket drivers are registered in sysTffsInit( ) at boot time. The first registered is drive 0, the second is drive 1, and so on up to 4. Details of this process are described in see the VxWorks Device Driver Developer’s Guide: Flash File System Support with TrueFFS. Specifying Format Options The second argument for tffsDevFormat( ), formatArg, is a pointer to a tffsDevFormatParams structure (cast to an int). This structure describes how the 552 10 Flash File System Support: TrueFFS 10.3 Creating a System with TrueFFS volume should be formatted. The tffsDevFormatParams structure is defined in installDir/vxworks-6.x/target/h/tffs/tffsDrv.h: typedef struct { tffsFormatParams formatParams; unsigned formatFlags; }tffsDevFormatParams; TFFS_STD_FORMAT_PARAMS To facilitate calling tffsDevFormat( ) from the shell, you can simply pass zero (or a NULL pointer) for the second argument, formatArg. Doing makes use of the TFFS_STD_FORMAT_PARAMS macro, which defines default values for the tffsDevFormatParams structure. The macro defines the default values used in formatting a flash disk device. Do not use this macro if the flash device is shared with a boot loader. If the BSP provides sysTffsFormat( ) use that routine instead. TFFS_STD_FORMAT_PARAMS is defined in tffsDrv.h as: #define TFFS_STD_FORMAT_PARAMS {{0, 99, 1, 0x10000l, NULL, {0,0,0,0}, NULL, 2, 0, NULL}, FTL_FORMAT_IF_NEEDED} If the second argument, formatArg, is zero, tffsDevFormat( ) uses the default values from this macro. The macro passes values for both the first and second members of the tffsDevFormatParams structure. These are: formatParams = {0, 99, 1, 0x10000l, NULL, {0,0,0,0}, NULL, 2, 0, NULL} formatFlags = FTL_FORMAT_IF_NEEDED The meaning of these default values, and other possible arguments for the members of this structure, are described below. formatParams The formatParams member is of the type tffsFormatParams. Both this structure, and the default values used by the TFFS_STD_FORMAT_PARAMS macro, are defined in installDir/vxworks-6.x/target/h/tffs/tffsDrv.h. If you use the TFFS_STD_FORMAT_PARAMS macro, the default values will format the entire flash medium for use with TrueFFS. If you want to store a boot image in flash, you must change the value of the bootImageLen member of the tffsFormatParams structure to reserve a region flash for the image, which is separate from that used by TrueFFS (for more information see 10.3.6 Reserving a Region in Flash for a Boot Image, p.554). 553 10 VxWorks Kernel Programmer's Guide, 6.6 formatFlags The second member of the tffsDevFormatParams structure, formatFlags, determines the option used to format the drive. There are several possible values for formatFlags, which are listed in Table 10-3. Table 10-3 Options for formatFlags Macro Value Meaning FTL_FORMAT 1 FAT and FTL formatting FTL_FORMAT_IF_NEEDED 2 FAT formatting, FTL formatting if needed NO_FTL_FORMAT 0 FAT formatting only The default macro TFFS_STD_FORMAT_PARAMS passes FTL_FORMAT_IF_NEEDED as the value for this argument. 10.3.6 Reserving a Region in Flash for a Boot Image In order to use flash media for a boot image as well as a file system, a portion of the flash memory (a fallow region) must be reserved so that it is excluded from the area subject to formatting and the run-time operations of TrueFFS. Note that the fallow region can be used for purposes other than boot loader code (for example, a system startup log or configuration data). If TrueFFS is used with the vxWorks_romResident VxWorks image type, TrueFFS must be read-only. For information about boot image types, see 3.3 Boot Loader Image Types, p.133 and 2.4.1 VxWorks Image Types, p.15. Reserving a Fallow Region To create a boot image region, TrueFSS must be configured so that it is excluded from an area of flash that is large enough to accommodate the boot image. If your BSP provides sysTffsFormat( ), you can use the routine to do so. Otherwise, you must modify the tffsFormatParams structure. Using sysTffsFormat( ) Some BSPs provide an optional, BSP-specific, helper routine sysTffsFormat( ), which can be used to preserve a boot image region. 554 10 Flash File System Support: TrueFFS 10.3 Creating a System with TrueFFS This routine first sets up a pointer to a tffsFormatParams structure that has been initialized with a value for bootImageLen (which defines the boot image region); then it calls tffsDevFormat( ). Several BSPs, among them the ads860 BSP, include a sysTffsFormat( ) routine that reserves 0.5 MB for the boot image. For example: STATUS sysTffsFormat (void) { STATUS status; tffsDevFormatParams params = { #define HALF_FORMAT /* lower 0.5MB for bootimage, upper 1.5MB for TFFS */ #ifdef HALF_FORMAT {0x80000l, 99, 1, 0x10000l, NULL, {0,0,0,0}, NULL, 2, 0, NULL}, #else {0x000000l, 99, 1, 0x10000l, NULL, {0,0,0,0}, NULL, 2, 0, NULL}, #endif /* HALF_FORMAT */ FTL_FORMAT_IF_NEEDED }; /* assume that the drive number 0 is SIMM */ status = tffsDevFormat (0, (int)¶ms); return (status); } For more examples of sysTffsFormat( ) usage, see the socket drivers in installDir/vxworks-6.x/target/src/drv/tffs/sockets. If your BSP does not provide a sysTffsFormat( ) routine, then create a similar routine, or pass the appropriate argument to tffsDevFormat( ). Modifying the tffsFormatParams Structure If your BSP does not provide sysTffsFormat( ), you must modify the tffsFormatParams structure to reserve a fallow region before you call tffsDevFormat( ). Change the bootImageLen member of the tffsFormatParams structure to a value that is at least as large as the boot image. The area defined by bootImageLen is excluded from TrueFFS activity (formatting and wear-leveling). For more information about bootImageLen and other members of the structure, see Specifying Format Options, p.552. 555 10 VxWorks Kernel Programmer's Guide, 6.6 Writing the Boot Image to Flash Once you have created a boot image region, you can write the boot image to the flash device using tffsBootImagePut( ). This routine bypasses TrueFFS (and its translation layer) and writes directly into any location in flash memory. However, because tffsBootImagePut( ) relies on a call to tffsRawio( ), you cannot use this routine once the TrueFFS volume is mounted. The arguments to tffsBootImagePut( ) are the following: driveNo The same drive number as the one used as input to the format routine. offset Offset from the start of flash at which the image is written (most often specified as zero). filename Pointer to the boot image. ! WARNING: Because tffsBootImagePut( ) lets you write directly to any area of flash, it is possible to accidentally overwrite and corrupt the TrueFFS-managed area of flash if you do not specify the parameters correctly. For more information about how to use this utility, see the reference entry for tffsBootImagePut( ) in the VxWorks API reference. 10.3.7 Mounting the Drive Use the usrTffsConfig( ) routine to mount the file system on a TrueFFS flash drive. Its arguments are the following: drive Specifies the drive number of the TFFS flash drive; valid values are 0 through the number of socket interfaces in BSP. removable Specifies whether the media is removable. Use 0 for non-removable, 1 for removable. fileName Specifies the mount point, for example, '/tffs0/'. 556 10 Flash File System Support: TrueFFS 10.3 Creating a System with TrueFFS The following example runs usrTffsConfig( ) to attach a drive to the file system, and then runs devs to list all drivers: -> usrTffsConfig 0,0,"/flashDrive0/" -> devs drv 0 1 1 5 6 2 name /null /tyCo/0 /tyCo/1 host: /vio /flashDrive0/ Internally, usrTffsConfig( ) calls other routines, passing the parameters it is given. Among these routines is tffsDevCreate( ), which creates a TrueFFS block device on top of the socket driver. This routine takes, as input, a number (0 through 4) that identifies the socket driver on top of which to construct the TrueFFS block device. The tffsDevCreate( ) call uses this number as an index into the array of FLSocket structures. This number is visible later to the file system as the driver number. The xbdBlkDevCreateSync( ) routine is then called, which sends a message the file system handler. If the TFFS device has a valid file system installed (dosFS or HRFS) the file system handler mounts the underlying file system. If there is no valid file system on the device, rawfs is instantiated on the device. The user can then format the device with the file system of choice. After mounting the drive, create the file system (dosFs or HRFS). 10.3.8 Testing the Drive One way to test your drive is by copying a text file from the host (or from another type of storage medium) to the flash file system on the target. Then, copy the file to the console or to a temporary file for comparison, and verify the content. The following example (using dosFs on TrueFFS) is run from the shell: ->@copy "host:/home/myHost/.cshrc" "/flashDrive0/myCshrc" Copy Ok: 4266 bytes copied Value = 0 = 0x0 ->@copy "/flashDrive0/myCshrc" ... ... ... Copy Ok: 4266 bytes copied Value = 0 = 0x0 557 10 VxWorks Kernel Programmer's Guide, 6.6 NOTE: The copy command requires the appropriate configuration of dosFs support components. For more information on dosFs, see 8.5.1 Configuring VxWorks for dosFs, p.478. 10.4 Using TrueFFS Shell Commands This section illustrates using TrueFFS shell commands (with the C interpreter) to access the flash file system. These examples assume that the flash has been configured into the system in the default configuration for the BSPs shown. For detailed information on creating a system with TrueFFS, 10.2 Overview of Implementation Steps, p.545 and 10.3 Creating a System with TrueFFS, p.546. Target with a Board-Resident Flash Array and a Boot Image Region This example uses sysTffsFormat( ) to format board-resident flash, preserving the boot image region. It does not update the boot image, so no call is made to tffsBootImagePut( ). Then, it mounts the non-removable RFA medium as drive number 0. At the shell prompt, type the following commands: -> sysTffsFormat -> usrTffsConfig 0,0,"/RFA/" Target with a Board-Resident Flash Array and a PCMCIA Slot This example formats RFA and PCMCIA flash for two drives. The first lines of this example format the board-resident flash by calling the helper routine, sysTffsFormat( ), which preserves the boot image region. This example does not update the boot image. It then mounts the drive, numbering it as 0 and passing 0 as the second argument to usrTffsConfig( ). Zero is used because RFA is non-removable. The last lines of the example format PCMCIA flash, passing default format values to tffsDevFormat( ) for formatting the entire drive. Then, it mounts that drive. Because PCMCIA is removable flash, it passes 1 as the second argument to usrTffsConfig( ). (See 10.3.7 Mounting the Drive, p.556 for details on the arguments to usrTffsConfig( ).) 558 10 Flash File System Support: TrueFFS 10.4 Using TrueFFS Shell Commands Insert a flash card in the PCMCIA socket. At the shell prompt, type the following commands: -> -> -> -> sysTffsFormat usrTffsConfig 0,0,"/RFA/" tffsDevFormat 1,0 usrTffsConfig 1,1,"/PCMCIA1/" Target with a Board-Resident Flash Array and No Boot Image Region Created This example formats board-resident flash using the default parameters to tffsDevFormat( ), as described in 10.3.5 Formatting the Flash, p.552. Then, it mounts the drive, passing 0 as the drive number and indicating that the flash is non-removable. At the shell prompt, type the following commands: 10 -> tffsDevFormat 0,0 -> usrTffsConfig 0,0,"/RFA/" Target with Two PCMCIA Slots This example formats PCMCIA flash for two drives. Neither format call preserves a boot image region. Then, it mounts the drives, the first is numbered 0, and the second is numbered 1. PCMCIA is a removable medium. Insert a flash card in each PCMCIA socket. At the shell prompt, type the following commands: -> -> -> -> tffsDevFormat usrTffsConfig tffsDevFormat usrTffsConfig 0,0 0,1,"/PCMCIA1/" 1,0 1,1,"/PCMCIA2/" 559 VxWorks Kernel Programmer's Guide, 6.6 10.5 Using TrueFFS With HRFS This section provides information about implementing TrueFFS with HRFS programmatically, as well as interactively from the kernel shell. 10.5.1 TrueFFS With HRFS Code Example The following code fragment illustrates the procedure for creating a TrueFFS block device, creating an XBD block device wrapper, and formatting the TrueFFS media for an HRFS file system. /* create block device for the entire disk, */ if ((pBlkDev = tffsDevCreate (0, 0)) == NULL) { printErr ("tffsDevCreate failed."); return (ERROR); } /* wrap this block device into an XBD */ xbd = xbdBlkDevCreateSync(pBlkDev, "/tffs0"); printf("Wrap XBD=0x%x /* * If the HRFS file system exists already, it will be * automatically instantiated and we are done. */ /* * But if a file system does not exist or it isn't HRFS * format it. */ hrfsFormat ("/tffs0", 0, 0, 0); For a description of the full set of steps needed to implement HRFS with TrueFFS, see 10.5.2 TrueFFS With HRFS Shell Command Example, p.560. 10.5.2 TrueFFS With HRFS Shell Command Example The following steps illustrate the procedure for implementing TrueFFS with HRFS using the kernel shell. 560 10 Flash File System Support: TrueFFS 10.5 Using TrueFFS With HRFS 1. Perform a low-level format of the flash device. This step must be performed before you use the flash device for the first time. > sysTffsFormat value = 0 = 0x0 2. Create the TrueFFS block device. > dev = tffsDevCreate (0,0) New symbol "dev" added to kernel symbol table. dev = 0x1ffb840: value = 33536128 = 0x1ffb880 = dev + 0x40 3. Create an XBD device wrapper. > xbdBlkDevCreateSync dev, "/tffs" Instantiating /tffs:0 as rawFs, device = 0x10001 value = 1 = 0x1 4. Format the TrueFFS device for HRFS. > hrfsDiskFormat "/tffs:0" Formatting /tffs:0 for HRFS v1.2 Instantiating /tffs:0 as rawFs, device = 0x10001 Formatting...OK. value = 0 = 0x0 Note that the hrfsDiskFormat( ) routine is designed for convenient use from the shell; the hrfsFormat( ) routine is used in code. 5. The TFFS device is now ready for use. List the contents. > ll "/tffs:0" Listing Directory /tffs:0: drwxrwxrwx 1 0 0 8192 Jan 1 00:05 ./ drwxrwxrwx 1 0 0 8192 Jan 1 00:05 ../ value = 0 = 0x0 After the media and file system and been prepared, for subsequent reboots the procedure is slightly simpler as the flash media does not have to be formatted for TrueFFS and HRFS. 1. Create the TrueFFS block device. > dev = tffsDevCreate (0,0) New symbol "dev" added to kernel symbol table. dev = 0x461eb8: value = 33535048 = 0x1ffb448 2. Create an XBD device wrapper. > xbdBlkDevCreateSync dev, "/tffs" value = 1 = 0x1 3. The TFFS device is now ready for use. List the contents. > ll "/tffs:0" Listing Directory /tffs:0: drwxrwxrwx 1 0 0 8192 Jan 1 00:05 ./ drwxrwxrwx 1 0 0 8192 Jan 1 00:05 ../ value = 0 = 0x0 561 10 VxWorks Kernel Programmer's Guide, 6.6 562 11 Error Detection and Reporting 11.1 Introduction 563 11.2 Configuring Error Detection and Reporting Facilities 564 11.3 Error Records 566 11.4 Displaying and Clearing Error Records 568 11.5 Fatal Error Handling Options 569 11.6 Using Error Reporting APIs in Application Code 572 11.7 Sample Error Record 573 11.1 Introduction VxWorks provides an error detection and reporting facility to help debugging software faults. It does so by recording software exceptions in a specially designated area of memory that is not cleared between warm reboots. The facility also allows for selecting system responses to fatal errors, with alternate strategies for development and deployed systems. 563 VxWorks Kernel Programmer's Guide, 6.6 The key features of the error detection and reporting facility are: ■ A persistent memory region in RAM used to retain error records across warm reboots. ■ Mechanisms for recording various types of error records. ■ Error records that provide detailed information about run-time errors and the conditions under which they occur. ■ The ability to display error records and clear the error log from the shell. ■ Alternative error-handing options for the system’s response to fatal errors. ■ Macros for implementing error reporting in user code. The hook routines described in the edrLib API reference can be used as the basis for implementing custom functionality for non-RAM storage for error records. For more information about error detection and reporting routines in addition to that provided in this chapter, see the API reference entries for edrLib, edrShow, edrErrLogLib, and edrSysDbgLib. For information about related facilities, see 6.8 Memory Error Detection, p.331. NOTE: This chapter provides information about facilities available in the VxWorks kernel. For information about facilities available to real-time processes, see the corresponding chapter in the VxWorks Application Programmer’s Guide. 11.2 Configuring Error Detection and Reporting Facilities To use the error detection and reporting facilities: ■ VxWorks must be configured with the appropriate components. ■ A persistent RAM memory region must be configured, and it must be sufficiently large to hold the error records. ■ Optionally, users can change the system’s default response to fatal errors. 564 11 Error Detection and Reporting 11.2 Configuring Error Detection and Reporting Facilities 11.2.1 Configuring VxWorks To use the error detection and reporting facility, the kernel must be configured with the following components: ■ ■ ■ ■ INCLUDE_EDR_PM INCLUDE_EDR_ERRLOG INCLUDE_EDR_SHOW INCLUDE_EDR_SYSDBG_FLAG As a convenience, the BUNDLE_EDR component bundle may be used to include all of the above components. 11.2.2 Configuring the Persistent Memory Region The persistent-memory region is an area of RAM at the top of system memory specifically reserved for error records. It is protected by the MMU and the VxWorks vmLib facilities. The memory is not cleared by warm reboots, provided a VxWorks 6.x boot loader is used. NOTE: The persistent memory region is not supported for the symmetric multipro- cessing (SMP) configuration of VxWorks. For general information about VxWorks SMP and for information about migration, see 15. VxWorks SMP and 15.15 Migrating Code to VxWorks SMP, p.702. A cold reboot always clears the persistent memory region. The pmInvalidate( ) routine can also be used to explicitly destroy the region (making it unusable) so that it is recreated during the next warm reboot. The persistent-memory area is write-protected when the target system includes an MMU and VxWorks has been configured with MMU support. The size of the persistent memory region is defined by the PM_RESERVED_MEM configuration parameter. By default the size is set to six pages of memory. By default, the error detection and reporting facility uses one-half of whatever persistent memory is available. If no other applications require persistent memory, the component may be configured to use almost all of it. This can be accomplished by defining EDR_ERRLOG_SIZE to be the size of PM_RESERVED_MEM less the size of one page of memory. If you increase the size of the persistent memory region beyond the default, you must create a new boot loader with the same PM_RESERVED_MEM value. The memory area between RAM_HIGH_ADRS and sysMemTop( ) must be big enough 565 11 VxWorks Kernel Programmer's Guide, 6.6 to copy the VxWorks boot loader. If it exceeds the sysMemTop( ) limit, the boot loader may corrupt the area of persistent memory reserved for core dump storage when it loads VxWorks. The boot loader, must therefore be rebuilt with a lower RAM_HIGH_ADRS value. ! WARNING: If the boot loader is not properly configured (as described above), this could lead into corruption of the persistent memory region when the system boots. The EDR_RECORD_SIZE parameter can be used to change the default size of error records. Note that for performance reasons, all records are necessarily the same size. The pmShow( ) shell command (for the C interpreter) can be used to display the amount of allocated and free persistent memory. For more information about persistent memory, see 6.6 Reserved Memory, p.328 and the pmLib API reference. ! WARNING: A VxWorks 6.x boot loader must be used to ensure that the persistent memory region is not cleared between warm reboots. Prior versions of the boot loader may clear this area. 11.2.3 Configuring Responses to Fatal Errors The error detection and reporting facilities provide for two sets of responses to fatal errors. See 11.5 Fatal Error Handling Options, p.569 for information about these responses, and various ways to select one for a run-time system. 11.3 Error Records Error records are generated automatically when the system experiences specific kinds of faults. The records are stored in the persistent memory region of RAM in a circular buffer. Newer records overwrite older records when the persistent memory buffer is full. 566 11 Error Detection and Reporting 11.3 Error Records The records are classified according to two basic criteria: ■ ■ event type severity level The event type identifies the context in which the error occurred (during system initialization, or in a process, and so on). The severity level indicates the seriousness of the error. In the case of fatal errors, the severity level is also associated with alternative system’s responses to the error (see 11.5 Fatal Error Handling Options, p.569). The event types are defined in Table 11-1, and the severity levels in Table 11-2. Table 11-1 Table 11-2 Event Types Type Description INIT System initialization events. BOOT System boot events. REBOOT System reboot (warm boot) events. KERNEL VxWorks kernel events. INTERRUPT Interrupt handler events. RTP Process environment events. USER Custom events (user defined). 11 Severity Levels Severity Level Description FATAL Fatal event. NONFATAL Non-fatal event. WARNING Warning event. INFO Informational event. The information collected depends on the type of events that occurs. In general, a complete fault record is recorded. For some events, however, portions of the 567 VxWorks Kernel Programmer's Guide, 6.6 record are excluded for clarity. For example, the record for boot and reboot events exclude the register portion of the record. Error records hold detailed information about the system at the time of the event. Each record includes the following generic information: ■ ■ ■ ■ ■ ■ ■ ■ ■ date and time the record was generated type and severity operating system version task ID process ID, if the failing task in a process task name process name, if the failing task is in a process source file and line number where the record was created a free form text message It also optionally includes the following architecture-specific information: ■ ■ ■ ■ ■ memory map exception information processor registers disassembly listing (surrounding the faulting address) stack trace 11.4 Displaying and Clearing Error Records The edrShow library provides a set of commands for the shell’s C interpreter that are used for displaying the error records created since the persistent memory region was last cleared. See Table 11-3. Table 11-3 Shell Commands for Displaying Error Records Command Action edrShow( ) Show all records. edrFatalShow( ) Show only FATAL severity level records. edrInfoShow( ) Show only INFO severity level records. edrKernelShow( ) Show only KERNEL event type records. 568 11 Error Detection and Reporting 11.5 Fatal Error Handling Options Table 11-3 Shell Commands for Displaying Error Records (cont’d) Command Action edrRtpShow( ) Show only RTP (process) event type records. edrUserShow( ) Show only USER event type records. edrIntShow( ) Show only INTERRUPT event type records. edrInitShow( ) Show only INIT event type records. edrBootShow( ) Show only BOOT event type records. edrRebootShow( ) Show only REBOOT event type records. The shell’s command interpreter provides comparable commands. See the API references for the shell, or use the help edr command. In addition to displaying error records, each of the show commands also displays the following general information about the error log: ■ ■ ■ ■ ■ ■ ■ total size of the log size of each record maximum number of records in the log the CPU type a count of records missed due to no free records the number of active records in the log the number of reboots since the log was created See the edrShow API reference for more information. 11.5 Fatal Error Handling Options In addition to generating error records, the error detection and reporting facility provides for two modes of system response to fatal errors for each event type: ■ ■ debug mode, for lab systems (development) deployed mode, for production systems (field) The difference between these modes is in their response to fatal errors in processes (RTP events). In debug mode, a fatal error in a process results in the process being 569 11 VxWorks Kernel Programmer's Guide, 6.6 stopped. In deployed mode, as fatal error in a process results in the process being terminated. The operative error handling mode is determined by the system debug flag (see 11.5.2 Setting the System Debug Flag, p.571). The default is deployed mode. Table 11-4 describes the responses in each mode for each of the event types. It also lists the routines that are called when fatal records are created. The error handling routines are called response to certain fatal errors. Only fatal errors—and no other event types—have handlers associated with them. These handlers are defined in installDir/vxworks-6.x/target/config/comps/src/edrStub.c. Developers can modify the routines in this file to implement different system responses to fatal errors. The names of the routines, however, cannot be changed. Table 11-4 FATAL Error-Handling Options Event Type Debug Mode Deployed Mode (default) INIT Reboot Reboot edrInitFatalPolicyHandler( ) KERNEL Stop failed task Stop failed task edrKernelFatalPolicyHandler( ) INTERRUPT Reboot Reboot edrInterruptFatalPolicyHandler( ) RTP Stop process Delete process edrRtpFatalPolicyHandler( ) Error Handling Routine Note that when the debugger is attached to the target, it gains control of the system before the error-handling option is invoked, thus allowing the system to be debugged even if the error-handling option calls for a reboot. 11.5.1 Configuring VxWorks with Error Handling Options In order to provide the option of debug mode error handling for fatal errors, VxWorks must be configured with the INCLUDE_EDR_SYSDBG_FLAG component, which it is by default. The component allows a system debug flag to be used to select debug mode, as well as reset to deployed mode (see 11.5.2 Setting the System Debug Flag, p.571). If INCLUDE_EDR_SYSDBG_FLAG is removed from VxWorks, the system defaults to deployed mode (see Table 11-4). 570 11 Error Detection and Reporting 11.5 Fatal Error Handling Options 11.5.2 Setting the System Debug Flag How the error detection and reporting facility responds to fatal errors, beyond merely recording the error, depends on the setting of the system debug flag. When the system is configured with the INCLUDE_EDR_SYSDBG_FLAG component, the flag can be used to set the handling of fatal errors to either debug mode or deployed mode (the default). For systems undergoing development, it is obviously desirable to leave the system in a state that can be more easily debugged; while in deployed systems, the aim is to have them recover as best as possible from fatal errors and continue operation. The debug flag can be set in any of the following ways: ■ Statically, with boot loader configuration. ■ Interactively, at boot time. ■ Programmatically, using APIs in application code. 11 When a system boots, the banner displayed on the console displays information about the mode defined by the system debug flag. For example: ED&R Policy Mode: Deployed The modes are identified as Debug, Deployed, or Permanently Deployed. The latter indicates that the INCLUDE_EDR_SYSDBG_FLAG component is not included in the system, which means that the mode is deployed and that it cannot be changed to debug. For more information, see the following sections and the API reference entry for edrSysDbgLib (in particular with regard to the edrSystemDebugModeSet( ) routine). Setting the Debug Flag Statically The system can be set to either debug mode or deployed mode with the f boot loader parameter when a boot loader is configured and built. The value of 0x000 is used to select deployed mode. The value of 0x400 is used to select debug mode. By default, it is set to deployed mode. For information about configuring and building boot loaders, see 3.7 Customizing and Building Boot Loaders, p.146. 571 VxWorks Kernel Programmer's Guide, 6.6 Setting the Debug Flag Interactively To change the system debug flag interactively, stop the system when it boots. Then use the c command at the boot-loader command prompt. Change the value of the the f parameter: use 0x000 for deployed mode (the default) or to 0x400 for debug mode. Setting the Debug Flag Programmatically The state of the system debug flag can also be changed in user code with the edrSysDbgLib API. 11.6 Using Error Reporting APIs in Application Code The edrLib.h file provides a set of convenient macros that developers can use in their source code to generate error messages (and responses by the system to fatal errors) under conditions of the developers choosing. The macros have no effect if VxWorks has not been configured with error detection and reporting facilities. Code, therefore, must not be conditionally compiled to make use of these facilities. The edrLib.h file is in installDir/vxworks-6.x/target/h. The following macros are provided: EDR_USER_INFO_INJECT (trace, msg) Creates a record in the error log with an event type of USER and a severity of INFO. EDR_USER_WARNING_INJECT (trace, msg) Creates a record in the error log with event type of USER and a severity of WARNING. EDR_USER_FATAL_INJECT (trace, msg) Creates a record in the error log with event type of USER and a severity of FATAL. 572 11 Error Detection and Reporting 11.7 Sample Error Record All the macros use the same parameters. The trace parameter is a boolean value indicating whether or not a traceback should be generated for the record. The msg parameter is a string that is added to the record. 11.7 Sample Error Record The following is an example of a record generated by a failed kernel task: ==[1/1]============================================================== Severity/Facility: FATAL/KERNEL Boot Cycle: 1 OS Version: 6.0.0 Time: THU JAN 01 05:15:07 1970 (ticks = 1134446) Task: "kernelTask" (0x0068c6c8) Injection Point: excArchLib.c:2523 fatal kernel task-level exception! <<<< >>>> 0x00100000 -> 0x002a48dc: kernel <<<< >>>> data access Exception current instruction address: 0x002110cc Machine Status Register: 0x0000b032 Data Access Register: 0x50000000 Condition Register: 0x20000080 Data storage interrupt Register: 0x40000000 <<<< >>>> r0 r3 r6 r9 r12 r15 r18 r21 r24 r27 r30 lr cr scSrTblPtr = = = = = = = = = = = = = = 0x00210ff8 0x00213a10 0x0068c6c8 0x00000000 0x0000007f 0x00000000 0x00000000 0x00000000 0x00000000 0x00000000 0x00000000 0x00210ff8 0x20000080 0x0047fe4c sp r4 r7 r10 r13 r16 r19 r22 r25 r28 r31 ctr xer srTblPtr = = = = = = = = = = = = = = 0x006e0f50 0x00003032 0x0000003a 0x00000002 0x00000000 0x00000000 0x00000000 0x00000000 0x00000000 0x00000000 0x50000000 0x0024046c 0x20000000 0x0047fe4c r2 r5 r8 r11 r14 r17 r20 r23 r26 r29 msr pc pgTblPtr 573 = = = = = = = = = = = = = 0x00000000 0x00000001 0x00000000 0x00000002 0x00000000 0x00000000 0x00000000 0x00000000 0x00000000 0x006e0f74 0x0000b032 0x002110cc 0x00481000 11 VxWorks Kernel Programmer's Guide, 6.6 <<<< >>>> 0x2110ac 0x2110b0 0x2110b4 0x2110b8 0x2110bc 0x2110c0 0x2110c4 0x2110c8 *0x2110cc 0x2110d0 0x2110d4 0x2110d8 0x2110dc 0x2110e0 0x2110e4 0x2110e8 2c0b0004 41820024 2c0b0008 41820030 4800004c 3c600021 83e1001c 38633a10 a09f0000 48000048 83e1001c 3c600021 38633a15 809f0000 48000034 83e1001c cmpi bc cmpi bc b lis lwz addi lhz b lwz lis addi lwz b lwz crf0,0,r11,0x4 # 4 0xc,2, 0x2110d4 # 0x002110d4 crf0,0,r11,0x8 # 8 0xc,2, 0x2110e8 # 0x002110e8 0x211108 # 0x00211108 r3,0x21 # 33 r31,28(r1) r3,r3,0x3a10 # 14864 r4,0(r31) 0x211118 # 0x00211118 r31,28(r1) r3,0x21 # 33 r3,r3,0x3a15 # 14869 r4,0(r31) 0x211118 # 0x00211118 r31,28(r1) <<<< >>>> 0x0011047c vxTaskEntry 0x00211258 d 574 +0x54 : 0x00211244 () +0x18 : memoryDump () 12 Target Tools 12.1 Introduction 576 12.2 Kernel Shell 577 12.3 Kernel Object-Module Loader 603 12.4 Kernel Symbol Tables 617 12.5 Show Routines 624 12.6 WDB Target Agent 626 12.7 Common Problems 643 575 VxWorks Kernel Programmer's Guide, 6.6 12.1 Introduction The Wind River host development environment provides tools that reside and execute on the host machine. This approach conserves target memory and resources. However, there are many situations in which it is desirable to make use of target-resident facilities: a target-resident shell, kernel object-module loader, debugging facilities, and system symbol table. The uses for these target-resident tools include the following: ■ Debugging a deployed system over a serial connection. ■ Developing and debugging network protocols, where it is useful to see the target's view of a network. ■ Loading kernel modules from a target disk, from ROMFS, or over the network, and running them interactively (or programmatically). The target based tools are partially independent of each other. For example, the kernel shell may be used without the kernel object-module loader, and vice versa. However, for any of the other individual tools to be completely functional, the system symbol table is required. In some situations, it may be useful to use both the host-resident development tools and the target-resident tools at the same time. In this case, additional facilities are required so that both environments maintain consistent views of the system. For more information, see 12.4.5 Synchronizing Host and Kernel Modules List and Symbol Table, p.623. For the most part, the target-resident facilities work the same as their host development environment counterparts. For more information, see the appropriate chapters of the Wind River Workbench User’s Guide and the VxWorks Command-Line Tools User’s Guide. This chapter describes the target-resident kernel shell, kernel object-module loader, debugging facilities, and system symbol table. It also provides an overview of the most commonly used VxWorks show routines, which are executed from the shell. In addition, it describes the WDB target agent. WDB is a target-resident, run-time facility required for connecting host tools with a VxWorks target system. 576 12 Target Tools 12.2 Kernel Shell 12.2 Kernel Shell For the most part, the target-resident kernel shell works the same as the host shell (also known as WindSh—for Wind Shell).1 The kernel shell, however, supports only the C interpreter and command interpreter (see 12.2.2 Kernel and Host Shell Differences, p.578 for information about other differences). For detailed information about the host shell and the shell interpreters, see the Wind River Workbench Host Shell User’s Guide, and the online Wind River Host Shell API Reference. Multiple kernel shell sessions may be run simultaneously, which allows for simultaneous access to the target from the host console and remote connections made with telnet or rlogin. NOTE: The kernel shell operates only with int, long, short, char, double, or float data types. 12 12.2.1 C Interpreter and Command Interpreter The kernel shell includes both a C interpreter and a command interpreter. Their basic differences are as follows: ■ The command interpreter is designed primarily for starting, monitoring, and debugging real-time process (RTP) applications. It can also be used in conjunction with the kernel object module loader to load and unload kernel object modules. It provides a UNIX-like shell environment. ■ The C interpreter is designed primarily for monitoring and debugging kernel-based code. It can be used for loading, running, and unloading object modules in conjunction with the kernel object-module loader. In addition, it provides some APIs for starting and monitoring RTP applications. The C interpreter operates on C routines. For detailed information about the interpreters, see the Wind River Workbench Host Shell User’s Guide. For information about the commands supported by each interpreter, see Interpreter Commands and References, p.578. 1. In versions of VxWorks prior to 6.0, the kernel shell was called the target shell. The new name reflects the fact that the target-resident shell runs in the kernel and not in a process. 577 VxWorks Kernel Programmer's Guide, 6.6 For information about adding new commands to the command interpreter, and creating interpreters for the kernel shell, see 12.2.19 Adding Custom Commands to the Command Interpreter, p.594 and 12.2.20 Creating a Custom Interpreter, p.599. Switching Between Interpreters To switch between the shell’s C and command interpreters, use the cmd command when the C interpreter is active to invoke the command interpreter, and the C command when the command interpreter is active to invoke the C interpreter. The following example illustrates switching from the C interpreter to the command interpreter and back again (note the difference in the shell prompt for each interpreter): -> cmd [vxWorks *]# C -> You can also execute a command from the interpreter that is not active. Interpreter Commands and References For information about individual C interpreter routines, see the usrLib, dbgLib, and usrShellHistLib sections in the VxWorks Kernel API Reference, as well as entries for the various show routine libraries. The dbgLib routines are particularly useful (for example, semaphores can be created and manipulated from the shell). Note that the kernel shell can also call any C routine that returns a data type supported by the shell (int, long, short, char, double, or float). For information about the command interpreter commands, see the VxWorks Kernel Shell Command Reference. For information about help available from the kernel shell itself, see 12.2.6 Using Kernel Shell Help, p.585. 12.2.2 Kernel and Host Shell Differences The major differences between the target and host shells are: ■ 578 The host and kernel shells do not provide exactly the same set of commands. The kernel shell, for example, has commands related to network, shared data, 12 Target Tools 12.2 Kernel Shell environment variables, and some other facilities that are not provided by the host shell. However, the host and kernel shells provide a very similar set of commands for their command and C interpreters. ■ Each shell has its own distinct configuration parameters, as well as those that are common to both. ■ Both shells include a command and a C interpreter. The host shell also provides a Tcl interpreter and a gdb interpreter. The gdb interpreter has about 40 commands and is intended for debugging processes (RTPs); and it references host file system paths. ■ For the host shell to work, VxWorks must be configured with the WDB target agent component. For the kernel shell to work, VxWorks be configured with the kernel shell component, as well as the target-resident symbol tables component. ■ The host shell can perform many control and information functions entirely on the host, without consuming target resources. ■ The kernel shell does not require any Wind River host tool support. ■ The host shell uses host system resources for most functions, so that it remains segregated from the target. This means that the host shell can operate on the target from the outside, whereas the kernel shell is part of the VxWorks kernel. For example, because the kernel shell task is created with the taskSpawn( ) VX_UNBREAKABLE option, it is not possible to set breakpoints on a function executed within the kernel shell task context. Therefore, the user must create a new task, with sp( ), to make breakable calls. For example, from the kernel shell you must do this: -> b printf -> sp printf, "Test\n" Whereas from the host shell you can do this: -> b printf -> printf ("Test\n") Conflicts in task priority may also occur while using the kernel shell. ! WARNING: Shell commands must be used in conformance with the routine prototype, or they may cause the system to hang. ■ The kernel shell has its own set of terminal-control characters, unlike the host shell, which inherits its setting from the host window from which it was invoked. (See 12.2.7 Using Kernel Shell Control Characters, p.586.) 579 12 VxWorks Kernel Programmer's Guide, 6.6 ■ The kernel shell correctly interprets the tilde operator in pathnames for UNIX and Linux host systems (or remote file systems on a UNIX or Linux host accessed with ftp, rsh, NFS, and so on), whereas the host shell cannot. For example, the following command executed from the kernel shell (with the C interpreter) by user panloki would correctly locate the kernel module /home/panloki/foo.o on the host system and load it into the kernel: -> ld < ~/foo.o ■ When the kernel shell encounters a string literal (“...”) in an expression, it allocates space for the string, including the null-byte string terminator, plus some additional overhead.2 The value of the literal is the address of the string in the newly allocated storage. For example, the following expression allocates 12-plus bytes from the target memory pool, enters the string in that memory (including the null terminator), and assigns the address of the string to x: -> x = "hello there" The following expression can be used to return the memory to the target memory pool (see the memLib reference entry for information on memory management): -> free (x) Furthermore, even when a string literal is not assigned to a symbol, memory is still permanently allocated for it. For example, the following expression uses memory that is never freed: -> printf ("hello there") This is because if strings were only temporarily allocated, and a string literal was passed to a routine being spawned as a task, by the time the task executed and attempted to access the string, the kernel shell would have already released (and possibly even reused) the temporary storage where the string was held. If the accumulation of memory used for strings has an adverse effect on performance after extended development sessions with the kernel shell, you can use the strFree() routine (with the C interpreter) or the equivalent string free command (with the command interpreter). The host shell also allocates memory on the target if the string is to be used there. However, it does not allocate memory on the target for commands that can be performed at the host level (such as lkup( ), ld( ), and so on). 2. The amount of memory allocated is rounded up to the minimum allocation unit for the architecture in question, plus the amount for the header for that block of memory. 580 12 Target Tools 12.2 Kernel Shell 12.2.3 Configuring VxWorks With the Kernel Shell The functionality of the kernel shell is provided by a suite of components, some of which are required, and others of which are optional. Required Components To use the kernel shell, you must configure VxWorks with the INCLUDE_SHELL component. The configuration parameters for this component are described in Table 12-1. You must also configure VxWorks with components for symbol table support, using either the INCLUDE_STANDALONE_SYM_TBL or INCLUDE_NET_SYM_TBL component. For information about configuring VxWorks with symbol tables, see 12.4.1 Configuring VxWorks with Symbol Tables, p.618. Table 12-1 INCLUDE_SHELL Configuration Parameters 12 Configuration Parameter Description SHELL_SECURE Access the kernel shell attached to the console through a login access. SHELL_STACK_SIZE Default stack size of kernel shell task. SHELL_TASK_NAME_BASE Default basename for the kernel shell tasks. SHELL_TASK_PRIORITY Priority of the kernel shell tasks. SHELL_TASK_OPTIONS Spawning options for the kernel shell tasks. SHELL_START_AT_BOOT The kernel shell is launched automatically at boot time on the console. SHELL_COMPATIBLE The kernel shell is configured to be compatible with the vxWorks 5.5 shell: one shell session, global I/O redirected, shell task options without the VX_PRIVATE_ENV bit. SHELL_DEFAULT_CONFIG The default configuration parameters for the kernel shell can be set using this string. SHELL_FIRST_CONFIG The configuration parameters for