Creates simulation scripts that do not require manual updates for software or. IP version ... Manually instantiating the FIFO Intel FPGA IP core.
FIFO Intel® FPGA IP User Guide
Updated for Intel® Quartus® Prime Design Suite: 18.0
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Contents
Contents
FIFO Intel® FPGA IP User Guide......................................................................................... 3 Configuration Methods.................................................................................................. 3 Specifications.............................................................................................................. 4 Verilog HDL Prototype..........................................................................................4 VHDL Component Declaration............................................................................... 4 VHDL LIBRARY-USE Declaration............................................................................ 4 FIFO Signals.......................................................................................................4 FIFO Parameter Settings...................................................................................... 8 FIFO Functional Timing Requirements........................................................................... 11 SCFIFO ALMOST_EMPTY Functional Timing.................................................................... 12 FIFO Output Status Flag and Latency............................................................................ 13 FIFO Metastability Protection and Related Options...........................................................15 FIFO Synchronous Clear and Asynchronous Clear Effect...................................................17 Recovery and Removal Timing Violation Warnings when Compiling a DCFIFO.............18 SCFIFO and DCFIFO Show-Ahead Mode......................................................................... 19 Different Input and Output Width................................................................................. 20 DCFIFO Timing Constraint Setting.................................................................................21 Embedded Timing Constraint.............................................................................. 21 User Configurable Timing Constraint.................................................................... 22 Coding Example for Manual Instantiation....................................................................... 25 Design Example......................................................................................................... 26 Gray-Code Counter Transfer at the Clock Domain Crossing...............................................30 Guidelines for Embedded Memory ECC Feature...............................................................31 FIFO Intel FPGA IP User Guide Archives.........................................................................32 Document Revision History for the FIFO Intel FPGA IP User Guide..................................... 33
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FIFO Intel® FPGA IP User Guide
Intel® provides FIFO Intel FPGA IP core through the parameterizable single-clock FIFO (SCFIFO) and dual-clock FIFO (DCFIFO) functions. The FIFO functions are mostly applied in data buffering applications that comply with the first-in-first-out data flow in synchronous or asynchronous clock domains.
The specific names of the FIFO functions are as follows:
· SCFIFO: single-clock FIFO
· DCFIFO: dual-clock FIFO (supports same port widths for input and output data)
· DCFIFO_MIXED_WIDTHS: dual-clock FIFO (supports different port widths for input and output data)
Note:
The term "DCFIFO" refers to both the DCFIFO and DCFIFO_MIXED_WIDTHS functions, unless specified.
Related Information
· Introduction to Intel FPGA IP Cores Provides general information about all Intel FPGA IP cores, including parameterizing, generating, upgrading, and simulating IP cores.
· Creating Version-Independent IP and Platform Designer Simulation Scripts Creates simulation scripts that do not require manual updates for software or IP version upgrades.
· Project Management Best Practices Guidelines for efficient management and portability of your project and IP files.
· FIFO Intel FPGA IP User Guide Archives on page 32 Provides a list of user guides for previous versions of the FIFO Intel FPGA IP core.
Configuration Methods
Table 1.
Configuration Methods
You can configure and build the FIFO Intel FPGA IP core with methods shown in the following table.
Method
Description
Using the FIFO parameter editor.
Intel recommends using this method to build your FIFO Intel FPGA IP core. It is an efficient way to configure and build the FIFO Intel FPGA IP core. The FIFO parameter editor provides options that you can easily use to configure the FIFO Intel FPGA IP core.
continued...
Intel Corporation. All rights reserved. Agilex, Altera, Arria, Cyclone, Enpirion, Intel, the Intel logo, MAX, Nios, Quartus and Stratix words and logos are trademarks of Intel Corporation or its subsidiaries in the U.S. and/or other countries. Intel warrants performance of its FPGA and semiconductor products to current specifications in accordance with Intel's standard warranty, but reserves the right to make changes to any products and services at any time without notice. Intel assumes no responsibility or liability arising out of the application or use of any information, product, or service described herein except as expressly agreed to in writing by Intel. Intel customers are advised to obtain the latest version of device specifications before relying on any published information and before placing orders for products or services. *Other names and brands may be claimed as the property of others.
ISO 9001:2015 Registered
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Method Manually instantiating the FIFO Intel FPGA IP core.
Description
You can access the FIFO Intel FPGA IP core parameter editor in Basic Functions On Chip Memory FIFO of the IP catalog.(1)
Use this method only if you are an expert user. This method requires that you know the detailed specifications of the IP core. You must ensure that the input and output ports used, and the parameter values assigned are valid for the FIFO Intel FPGA IP core you instantiate for your target device.
Related Information
Introduction to Intel FPGA IP Cores Provides general information about the Intel Quartus® Prime Parameter Editor
Specifications
Verilog HDL Prototype
You can locate the Verilog HDL prototype in the Verilog Design File (.v) altera_mf.v in the <Intel Quartus® Prime installation directory>\eda\sim_lib directory.
VHDL Component Declaration
The VHDL component declaration is located in the <Intel Quartus Prime installation directory>\libraries\vhdl\altera_mf \altera_mf_components.vhd
VHDL LIBRARY-USE Declaration
The VHDL LIBRARY-USE declaration is not required if you use the VHDL Component Declaration.
LIBRARY altera_mf;
USE altera_mf.altera_mf_components.all;
FIFO Signals
This section provides diagrams of the SCFIFO and DCFIFO blocks of the FIFO Intel FPGA IP core to help in visualizing their input and output ports. This section also describes each port in detail to help in understanding their usages, functionality, or any restrictions. For better illustrations, some descriptions might refer you to a specific section in this user guide.
(1) Do not use dcfifo or scfifo as the entity name for your FIFO Platform Designer system.
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Figure 1.
SCFIFO and DCFIFO Input and Output Signals
SCFIFO
data[7..0] wrreq rdreq
q[7..0] full
almost_full
clock
empty
almost_empty
usedw[7..0]
sclr
eccstatus[1:0]
aclr
DCFIFO
data[7..0]
wrfull
wrreq
wrempty
wrclk wrusedw[8..0]
rdreq
q[7..0]
rdclk
rdfull
rdempty
rdusedw[8..0]
aclr
eccstatus[1:0]
For the SCFIFO block, the read and write signals are synchronized to the same clock; for the DCFIFO block, the read and write signals are synchronized to the rdclk and wrclk clocks respectively. The prefixes wr and rd represent the signals that are synchronized by the wrclk and rdclk clocks respectively.
Table 2.
Input and Output Ports Description
This table lists the signals of the FIFO Intel FPGA IP core. The term "series" refers to all the device families of a particular device. For example, "Stratix® series" refers to the Stratix IV and Stratix V, unless specified otherwise.
Port
Type Required
Description
clock (2)
Input
Yes
Positive-edge-triggered clock.
wrclk (3)
Input
Yes
Positive-edge-triggered clock.
Use to synchronize the following ports:
· data
· wrreq
· wrfull
· wrempty
· wrusedw
rdclk (3)
Input
Yes
Positive-edge-triggered clock.
Use to synchronize the following ports:
·q
· rdreq
· rdfull
· rdempty
· rdusedw
continued...
(2) Only applicable for the SCFIFO function. (3) Applicable for both of the DCFIFO functions.
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data (4)
Port
wrreq (4)
rdreq (4)
sclr (2) aclr (4) q (4)
full (2) wrfull (3) rdfull (3)
Type Input Input
Input
Input Output
Output
Required
Description
Yes
Holds the data to be written in the FIFO Intel FPGA IP core when
the wrreq signal is asserted. If you manually instantiate the FIFO
Intel FPGA IP core, ensure the port width is equal to the
lpm_width parameter.
Yes
Assert this signal to request for a write operation.
Ensure that the following conditions are met:
· Do not assert the wrreq signal when the full (for SCFIFO) or wrfull (for DCFIFO) port is high. Enable the overflow protection circuitry or set the overflow_checking parameter to ON so that the FIFO Intel FPGA IP core can automatically disable the wrreq signal when it is full.
· The wrreq signal must meet the functional timing requirement based on the full or wrfull signal.
· Do not assert the wrreq signal during the deassertion of the aclr signal. Violating this requirement creates a race condition between the falling edge of the aclr signal and the rising edge of the write clock if the wrreq port is set to high. For both the DCFIFO functions that target Stratix and Cyclone® series, you have the option to automatically add a circuit to synchronize the aclr signal with the wrclk clock, or set the write_aclr_synch parameter to ON. Use this option to ensure that the restriction is obeyed.
Yes
Assert this signal to request for a read operation. The rdreq
signal acts differently in normal mode and show-ahead mode.
Ensure that the following conditions are met:
· Do not assert the rdreq signal when the empty (for SCFIFO)
or rdempty (for DCFIFO) port is high. Enable the underflow protection circuitry or set the underflow_checking parameter to ON so that the FIFO Intel FPGA IP core can automatically disable the rdreq signal when it is empty.
· The rdreq signal must meet the functional timing requirement
based on the empty or rdempty signal.
No
Assert this signal to clear all the output status ports, but the effect
on the q output may vary for different FIFO configurations.
There are no minimum number of clock cycles for aclr signals that must remain active.
Yes
Shows the data read from the read request operation.
For the SCFIFO function and DCFIFO function, the width of the q port must be equal to the width of the data port. If you manually instantiate the FIFO functions, ensure that the port width is equal to the lpm_width parameter.
For the DCFIFO_MIXED_WIDTHS function, the width of the q port can be different from the width of the data port. If you manually instantiate the FIFO function, ensure that the width of the q port is equal to the lpm_width_r parameter. The FIFO function supports a wide write port with a narrow read port, and vice versa. However, the width ratio is restricted by the type of RAM block, and in general, are in the power of 2.
No
When asserted, the FIFO Intel FPGA IP core is considered full. Do
not perform write request operation when the FIFO Intel FPGA IP
core is full.
In general, the rdfull signal is a delayed version of the wrfull signal. However, for Stratix III devices and later, the rdfull signal functions as a combinational output instead of a derived
continued...
(4) Applicable for the SCFIFO, DCFIFO, and DCFIFO_MIXED_WIDTH functions.
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Port
empty (2) wrempty (3) rdempty (3)
almost_full (2) almost_empty (2) usedw (2) wrusedw (3) rdusedw (3)
eccstatus (6)
Type Output
Output Output Output
Output
Required
Description
version of the wrfull signal. Therefore, you must always refer to the wrfull port to ensure whether or not a valid write request operation can be performed, regardless of the target device.
No
When asserted, the FIFO Intel FPGA IP core is considered empty.
Do not perform read request operation when the FIFO Intel FPGA
IP core is empty.
In general, the wrempty signal is a delayed version of the rdempty signal. However, for Stratix III devices and later, the wrempty signal functions as a combinational output instead of a derived version of the rdempty signal. Therefore, you must always refer to the rdempty port to ensure whether or not a valid read request operation can be performed, regardless of the target device.
No
Asserted when the usedw signal is greater than or equal to the
almost_full_value parameter. It is used as an early indication
of the full signal.
No
Asserted when the usedw signal is less than the
almost_empty_value parameter. It is used as an early
indication of the empty signal. (5)
No
Show the number of words stored in the FIFO.
Ensure that the port width is equal to the lpm_widthu parameter if you manually instantiate the SCFIFO function or the DCFIFO function. For the DCFIFO_MIXED_WIDTH function, the width of the wrusedw and rdusedw ports must be equal to the LPM_WIDTHU and lpm_widthu_r parameters respectively.
For Stratix, Stratix GX, and Cyclone devices, the FIFO Intel FPGA IP core shows full even before the number of words stored reaches its maximum value. Therefore, you must always refer to the full or wrfull port for valid write request operation, and the empty or rdempty port for valid read request operation regardless of the target device.
Note: Stored data may not be available for reading. Refer to FIFO Output Status Flag and Latency on page 13 for "wrreq to empty" and "rdreq to empty" latency to ensure that the data is ready before reading the FIFO.
No
A 2-bit wide error correction status port. Indicate whether the data
that is read from the memory has an error in single-bit with
correction, fatal error with no correction, or no error bit occurs.
· 00: No error
· 01: Illegal
· 10: A correctable error occurred and the error has been corrected at the outputs; however, the memory array has not been updated.
· 11:An uncorrectable error occurred and uncorrectable data appears at the output.
This port is only available for Intel Arria® 10 devices using M20K memory block type.
(5) Under certain condition, the SCFIFO asserts the empty signal without ever asserting the almost_empty signal. Refer to SCFIFO ALMOST_EMPTY Functional Timing on page 12 for more details.
(6) Not applicable for the DCFIFO_MIXED_WIDTHS function.
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The DCFIFO functionrdempty output may momentarily glitch when the aclr input is asserted. To prevent an external register from capturing this glitch incorrectly, ensure that one of the following is true:
· The external register must use the same reset which is connected to the aclr input of the DCFIFO function, or
· The reset connected to the aclr input of the DCFIFO function must be asserted synchronous to the clock which drives the external register.
The output latency information of the FIFO Intel FPGA IP core is important, especially for the q output port, because there is no output flag to indicate when the output is valid to be sampled.
FIFO Parameter Settings
Table 3.
FIFO Parameters
Parameter
lpm_width
lpm_width_r (7) lpm_widthu
lpm_widthu_r (7) lpm_numwords
lpm_showahead
lpm_type
Type Required
Description
Integer
Yes
Specifies the width of the data and q ports for the SCFIFO
function and DCFIFO function. For the
DCFIFO_MIXED_WIDTHS function, this parameter specifies
only the width of the data port.
Integer
Yes
Specifies the width of the q port for the
DCFIFO_MIXED_WIDTHS function.
Integer
Yes
Specifies the width of the usedw port for the SCFIFO
function, or the width of the rdusedw and wrusedw ports
for the DCFIFO function. For the DCFIFO_MIXED_WIDTHS
function, it only represents the width of the wrusedw port.
Integer
Yes
Specifies the width of the rdusedw port for the
DCFIFO_MIXED_WIDTHS function.
Integer
Yes
Specifies the depths of the FIFO you require. The value
must be at least 4.
The value assigned must comply to the following equation:
2^LPM_WIDTHU
String
Yes
Specifies whether the FIFO is in normal mode (OFF) or
show-ahead mode (ON). For more details, refer to SCFIFO and DCFIFO Look-Ahead Mode section.
If you set the parameter to ON, you may reduce performance.
String
No
Identifies the library of parameterized modules (LPM)
entity name. The values are SCFIFO and DCFIFO.
continued...
(7) Only applicable for the DCFIFO_MIXED_WIDTHS function.
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Parameter lpm_hint
overflow_checking underflow_checking enable_ecc (8) delay_wrusedw (9) add_usedw_msb_bit (9)
Type String
String String String String String
Required
Description
No
This is a legacy parameter that is used to set the
following:
1. Maximum depth. You can set the maximum depth desired with "MAXIMUM_DEPTH=<depth>". Allow the Intel Quartus Prime software to automatically choose the maximum depth of the RAM used in SCFIFO by ignoring this parameter.
2. RAM block type. You can select the RAM block type with "RAM_BLOCK_TYPE=<M20K|MLAB|AUTO>". The default value is AUTO.
3. Disable Embedded Timing Constraint. This is a compulsory parameter to be set for DCFIFO on Intel Arria 10 device family onwards, which disables the legacy set_false_path that resides in FIFO Intel FPGA IP. Add "DISABLE_EMBEDDED_TIMING_CONSTRAINT=TRUE" to lpm_hint for proper timing analysis on the synchronizer path within DCFIFO IP.
Options should be concatenated with a comma in between and enclosed with double quotations. For example:
lpm_hint = "MAXIMUM_DEPTH=512, RAM_BLOCK_TYPE=M20K"
No
Specifies whether or not to enable the protection circuitry
for overflow checking that disables the wrreq port when
the FIFO Intel FPGA IP core is full. The values are ON or
OFF. If omitted, the default is ON.
No
Specifies whether or not to enable the protection circuitry
for underflow checking that disables the rdreq port when the FIFO Intel FPGA IP core is empty. The values are ON or OFF. If omitted, the default is ON.
Note that reading from an empty SCFIFO gives unpredictable results.
No
Specifies whether to enable the error checking and
correcting (ECC) feature that corrects single bit errors,
double adjacent bit errors, and detects triple adjacent bit
errors at the output of the memory. This option is only
available for Intel Arria 10 devices using M20K memory
block type.
The ECC is disabled by default.
No
Specify the number of register stages that you want to
internally add to the rdusedw or wrusedw port using the
respective parameter.
The default value of 1 adds a single register stage to the output to improve its performance. Increasing the value of the parameter does not increase the maximum system speed. It only adds additional latency to the respective output port.
No
Increases the width of the rdusedw and wrusedw ports
by one bit. By increasing the width, it prevents the FIFO
Intel FPGA IP core from rolling over to zero when it is full.
The values are ON or OFF. If omitted, the default value is
OFF.
continued...
(8) Not applicable for the DCFIFO_MIXED_WIDTHS function. (9) Only applicable for the DCFIFO function.
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Parameter rdsync_delaypipe (9) wrsync_delaypipe (9)
use_eab write_aclr_synch (9) read_aclr_synch (9) clocks_are_synchronized (9)
ram_block_type
Type Required
Description
Integer
No
Specify the number of synchronization stages in the cross
clock domain. The value of the rdsync_delaypipe parameter relates the synchronization stages from the write control logic to the read control logic; the
wrsync_delaypipe parameter relates the synchronization stages from the read control logic to the write control logic. Use these parameters to set the number of synchronization stages if the clocks are not
synchronized, and set the clocks_are_synchronized
parameter to FALSE.
The actual synchronization stage implemented relates variously to the parameter value assigned, depends on the target device.
The values of these parameters are internally reduced by two. Thus, the default value of 3 for these parameters corresponds to a single synchronization stage; a value of 4 results in two synchronization stages, and so on. Choose at least 4 (two synchronization stages) for metastability protection.
String
No
Specifies whether or not the FIFO Intel FPGA IP core is
constructed using the RAM blocks. The values are ON or
OFF.
Setting this parameter value to OFF yields the FIFO Intel FPGA IP core implemented in ALMs regardless of the type of the TriMatrix memory block type assigned to the ram_block_type parameter.
This parameter is enabled by default. FIFO will be implemented using RAM blocks specified in ram_block_type.
String
No
Specifies whether or not to add a circuit that causes the
aclr port to be internally synchronized by the wrclk clock. Adding the circuit prevents the race condition
between the wrreq and aclr ports that could corrupt the FIFO Intel FPGA IP core.
The values are ON or OFF. If omitted, the default value is OFF. This parameter is only applicable for Stratix and Cyclone series.
String
No
Specifies whether or not to add a circuit that causes the
aclr port to be internally synchronized by the rdclk
clock. Adding the circuit prevents the race condition
between the rdreq and aclr ports that could corrupt the
FIFO Intel FPGA IP core.
The values are ON or OFF. If omitted, the default value is OFF.
String
No
Specifies whether or not the write and read clocks are
synchronized which in turn determines the number of
internal synchronization stages added for stable operation
of the FIFO. The values are TRUE and FALSE. If omitted,
the default value is FALSE. You must only set the
parameter to TRUE if the write clock and the read clock
are always synchronized and they are multiples of each
other. Otherwise, set this to FALSE to avoid metastability
problems.
If the clocks are not synchronized, set the parameter to FALSE, and use the rdsync_delaypipe and wrsync_delaypipe parameters to determine the number of synchronization stages required.
String
No
Specifies the target device's Trimatrix Memory Block to be
used. To get the proper implementation based on the RAM
configuration that you set, allow the Intel Quartus Prime
continued...
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Parameter
add_ram_output_register
almost_full_value (10) almost_empty_value (10) allow_wrcycle_when_full (10) intended_device_family
Type Required
Description
software to automatically choose the memory type by ignoring this parameter and set the use_eab parameter to ON. This gives the compiler the flexibility to place the memory function in any available memory resource based on the FIFO depth required. Types of RAM block type available; Auto (default), MLAB, M20K and M144K.
String
No
Specifies whether to register the q output. The values are
ON and OFF. If omitted, the default value is OFF.
You can set the parameter to ON or OFF for the SCFIFO or the DCFIFO, that do not target Stratix II, Cyclone II, and new devices. This parameter does not apply to these
devices because the q output must be registered in normal
mode and unregistered in show-ahead mode for the DCFIFO.
Integer
No
Sets the threshold value for the almost_full port. When
the number of words stored in the FIFO Intel FPGA IP core
is greater than or equal to this value, the almost_full
port is asserted.
Integer
No
Sets the threshold value for the almost_empty port.
When the number of words stored in the FIFO Intel FPGA
IP core is less than this value, the almost_empty port is
asserted.
String
No
Allows you to combine read and write cycles to an already
full SCFIFO, so that it remains full. The values are ON and
OFF. If omitted, the default is OFF. Use only this
parameter when the OVERFLOW_CHECKING parameter is
set to ON.
String
No
Specifies the intended device that matches the device set
in your Intel Quartus Prime project. Use only this
parameter for functional simulation.
FIFO Functional Timing Requirements
The wrreq signal is ignored (when FIFO is full) if you enable the overflow protection circuitry in the FIFO Intel FPGA IP parameter editor, or set the OVERFLOW_CHECKING parameter to ON. The rdreq signal is ignored (when FIFO is empty) if you enable the underflow protection circuitry in the FIFO Intel FPGA IP core interface, or set the UNDERFLOW_CHECKING parameter to ON.
If the protection circuitry is not enabled, you must meet the following functional timing requirements:
Table 4.
Functional Timing Requirements
DCFIFO
SCFIFO
Deassert the wrreq signal in the same clock cycle when the Deassert the wrreq signal in the same clock cycle when the
wrfull signal is asserted.
full signal is asserted.
Deassert the rdreq signal in the same clock cycle when the rdempty signal is asserted. You must observe these requirements regardless of expected behavior based on wrclk and rdclk frequencies.
Deassert the rdreq signal in the same clock cycle when the empty signal is asserted.
(10) Only applicable for the SCFIFO function.
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Figure 2.
Functional Timing for the wrreq Signal and the wrfull Signal
This figure shows the behavior for the wrreq and the wrfull signals.
Figure 3.
Functional Timing for the rdreq Signal and the rdempty Signal
This shows the behavior for the rdreq the rdempty signals.
The required functional timing for the DCFIFO as described previously is also applied to the SCFIFO. The difference between the two modes is that for the SCFIFO, the wrreq signal must meet the functional timing requirement based on the full signal and the rdreq signal must meet the functional timing requirement based on the empty signal.
SCFIFO ALMOST_EMPTY Functional Timing
In SCFIFO, the almost_empty is asserted only when the usedw is less than the almost_empty_value that you set. The almost_empty signal does not consider the data readiness at the output. When the almost_empty_value is set too low, it is possible to observe that SCFIFO asserts the empty signal without asserting the almost_emtpy signal.
Figure 4. Example of empty Signal Assertion without Asserting almost_empty Signal
In this example, the almost_empty_value is 1 which means the almost_empty will assert when usedw is 0. There are three words in the FIFO before the read request is received. After the first read, the wrreq asserts and the rdreq signal remains high.
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The usedw remains at 2. In the next cycle, the wrreq de-asserts but there is another rdreq going on. The usedw decrease to 1 and the almost_emtpy signal remains low. However, the write data has not been written into the FIFO due to the write latency. The empty signal asserts to indicate the FIFO is empty.
FIFO Output Status Flag and Latency
The main concern in most FIFO design is the output latency of the read and write status signals.
Table 5.
Output Latency of the Status Flags for SCFIFO
This table shows the output latency of the write signal (wrreq) and read signal (rdreq) for the SCFIFO according to the different output modes and optimization options.
Output Mode Normal (13)
Optimization Option (11) Speed
Output Latency (in number of clock cycles) (12) wrreq / rdreq to full: 1
wrreq to empty: 2
rdreq to empty: 1
wrreq / rdreq to usedw[]: 1
rdreq to q[]: 1
Area
wrreq / rdreq to full: 1
wrreq / rdreq to empty : 1
wrreq / rdreq to usedw[] : 1
Show-ahead (13)
Speed
rdreq to q[]: 1 wrreq / rdreq to full: 1
wrreq to empty: 3
rdreq to empty: 1
wrreq / rdreq to usedw[]: 1
wrreq to q[]: 3
rdreq to q[]: 1
Area
wrreq / rdreq to full: 1
wrreq to empty: 2
rdreq to empty: 1
continued...
(11) Speed optimization is equivalent to setting the ADD_RAM_OUTPUT_REGISTER parameter to ON. Setting the parameter to OFF is equivalent to area optimization.
(12) The information of the output latency is applicable for Stratix and Cyclone series only. It may not be applicable for legacy devices such as the APEX® and FLEX® series.
(13) Normal output mode is equivalent to setting the LPM_SHOWAHEAD parameter to OFF. For Show-ahead mode, the parameter is set to ON.
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Output Mode
Optimization Option (11)
Output Latency (in number of clock cycles) (12)
wrreq / rdreq to usedw[]: 1
wrreq to q[]: 2
rdreq to q[]: 1
Table 6.
ALM Implemented RAM Mode for SCFIFO and DCFIFO
Output Mode Normal (16)
Optimization Option (14)
Output Latency (in number of clock cycles) (15)
Speed
wrreq / rdreq to full: 1
wrreq to empty: 1
rdreq to empty: 1
wrreq / rdreq to usedw[]: 1
rdreq to q[]: 1
Area
wrreq / rdreq to full: 1
wrreq / rdreq to empty : 1
wrreq / rdreq to usedw[] : 1
Show-ahead (16)
Speed
rdreq to q[]: 1 wrreq / rdreq to full: 1
wrreq to empty: 1
rdreq to empty: 1
wrreq / rdreq to usedw[]: 1
wrreq to q[]: 1
rdreq to q[]: 1
Area
wrreq / rdreq to full: 1
wrreq to empty: 1
rdreq to empty: 1
continued...
(11) Speed optimization is equivalent to setting the ADD_RAM_OUTPUT_REGISTER parameter to ON. Setting the parameter to OFF is equivalent to area optimization.
(12) The information of the output latency is applicable for Stratix and Cyclone series only. It may not be applicable for legacy devices such as the APEX® and FLEX® series.
(14) Speed optimization is equivalent to setting the ADD_RAM_OUTPUT_REGISTER parameter to ON. Setting the parameter to OFF is equivalent to area optimization.
(15) The information of the output latency is applicable for Stratix and Cyclone series only. It may not be applicable for legacy devices such as the APEX® and FLEX® series.
(16) Normal output mode is equivalent to setting the LPM_SHOWAHEAD parameter to OFF. For Show-ahead mode, the parameter is set to ON.
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Output Mode
Optimization Option (14)
Output Latency (in number of clock cycles) (15)
wrreq / rdreq to usedw[]: 1
wrreq to q[]: 1
rdreq to q[]: 1
Table 7.
Output Latency of the Status Flag for the DCFIFO
This table shows the output latency of the write signal (wrreq) and read signal (rdreq) for the DCFIFO.
Output Latency (in number of clock cycles) (17)
wrreq to wrfull: 1 wrclk
wrreq to rdfull: 2 wrclk cycles + following n rdclk (18)
wrreq to wrempty: 1 wrclk
wrreq to rdempty: 2 wrclk (19) + following n rdclk (19)
wrreq to wrusedw[]: 2 wrclk
wrreq to rdusedw[]: 2 wrclk + following n + 1 rdclk (19)
wrreq to q[]: 1 wrclk + following 1 rdclk (19)
rdreq to rdempty: 1 rdclk
rdreq to wrempty: 1 rdclk + following n wrclk (19)
rdreq to rfull: 1 rdclk
rdreq to wrfull: 1 rdclk + following n wrclk (19)
rdreq to rdusedw[]: 2 rdclk
rdreq to wrusedw[]: 1 rdclk + following n + 1 wrclk (19)
rdreq to q[]: 1 rdclk
FIFO Metastability Protection and Related Options
The FIFO Intel FPGA IP parameter editor provides the total latency, clock synchronization, metastability protection, area, and fMAX options as a group setting for the DCFIFO.
(14) Speed optimization is equivalent to setting the ADD_RAM_OUTPUT_REGISTER parameter to ON. Setting the parameter to OFF is equivalent to area optimization.
(15) The information of the output latency is applicable for Stratix and Cyclone series only. It may not be applicable for legacy devices such as the APEX® and FLEX® series.
(17) The output latency information is only applicable for Arria® GX, Stratix, and Cyclone series.
(18) The number of n cycles for rdclk and wrclk is equivalent to the number of synchronization stages and are related to the WRSYNC_DELAYPIPE and RDSYNC_DELAYPIPE parameters. For more information about how the actual synchronization stage (n) is related to the parameters set for different target device, refer to Table 9 on page 16.
(19) This is applied only to Show-ahead output modes. Show-ahead output mode is equivalent to setting the LPM_SHOWAHEAD parameter to ON.
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Table 8.
DCFIFO Group Setting for Latency and Related Options
This table shows the available group setting.
Group Setting
Comment
Lowest latency but requires synchronized clocks
This option uses one synchronization stage with no metastability protection. It uses the smallest size and provides good fMAX.
Select this option if the read and write clocks are related clocks.
Minimal setting for unsynchronized clocks
Best metastability protection, best fmax and unsynchronized clocks
This option uses two synchronization stages with good metastability protection. It uses the medium size and provides good fMAX.
This option uses three or more synchronization stages with the best metastability protection. It uses the largest size but gives the best fMAX.
The group setting for latency and related options is available through the FIFO Intel FPGA IP parameter editor. The setting mainly determines the number of synchronization stages, depending on the group setting you select. You can also set the number of synchronization stages you desire through the WRSYNC_DELAYPIPE
and RDSYNC_DELAYPIPE parameters, but you must understand how the actual number of synchronization stages relates to the parameter values set in different target devices.
The number of synchronization stages set is related to the value of the WRSYNC_DELAYPIPE and RDSYNC_DELAYPIPE pipeline parameters. For some cases, these pipeline parameters are internally scaled down by two to reflect the actual synchronization stage.
Table 9.
Relationship between the Actual Synchronization Stage and the Pipeline Parameters for Different Target Devices
This table shows the relationship between the actual synchronization stage and the pipeline parameters.
Stratix II, Cyclone II, and later
Other Devices
Actual synchronization stage = value of pipeline parameter - Actual synchronization stage = value of pipeline parameter 2 (20)
The Timing Analyzer includes the capability to estimate the robustness of asynchronous transfers in your design, and to generate a report that details the mean time between failures (MTBF) for all detected synchronization register chains. This report includes the MTBF analysis on the synchronization pipeline you applied between the asynchronous clock domains in your DCFIFO. You can then decide the number of synchronization stages to use in order to meet the range of the MTBF specification you require.
Related Information
· Timing Closure and Optimization Provides information about enabling metastability analysis and reporting.
(20) The values assigned to WRSYNC_DELAYPIPE and RDSYNC_DELAYPIPE parameters are internally reduced by 2 to represent the actual synchronization stage implemented. Thus, the default value 3 for these parameters corresponds to a single synchronization pipe stage; a value of 4 results in 2 synchronization stages, and so on. For these devices, choose 4 (2 synchronization stages) for metastability protection.
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· Area Optimization Provides information about enabling metastability analysis and reporting.
· The TimeQuest Timing Analyzer Provides information about enabling metastability analysis and reporting.
FIFO Synchronous Clear and Asynchronous Clear Effect
The FIFO Intel FPGA IP core supports the synchronous clear (sclr) and asynchronous
clear (aclr) signals, depending on the FIFO modes.The effects of these signals are varied for different FIFO configurations. The SCFIFO supports both synchronous and asynchronous clear signals while the DCFIFO support asynchronous clear signal and asynchronous clear signal that synchronized with the write and read clocks.
Table 10. Synchronous Clear and Asynchronous Clear in the SCFIFO
Mode
Synchronous Clear (sclr) (21)
Asynchronous Clear (aclr)
Effects on status ports
Deasserts the full and almost_full signals.
Asserts the empty and almost_empty signals.
Resets the usedw flag.
Commencement of effects upon assertion
At the rising edge of the clock.
Immediate (except for the q output)
Effects on the q output for normal output modes
The read pointer is reset and points to the first data location. If the q output is not registered, the output shows the first data word of the SCFIFO; otherwise, the q output remains at its previous value.
The q output remains at its previous value.
Effects on the q output for show-ahead output modes
The read pointer is reset and points to the first data location. If the q output is not registered, the output remains at its previous value for only one clock cycle and shows the first data word of the SCFIFO at the next rising clock edge. (22)
Otherwise, the q output remains at its previous value.
If the q output is not registered, the output shows the first data word of the SCFIFO starting at the first rising clock edge.
Otherwise, the q output remains its previous value.
(21) The read and write pointers reset to zero upon assertion of either the sclr or aclr signal.
(22) The first data word shown after the reset is not a valid Show-ahead data. It reflects the data where the read pointer is pointing to because the q output is not registered. To obtain a valid Show-ahead data, perform a valid write after the reset.
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Table 11. Asynchronous Clear in DCFIFO
Mode Effects on status ports
Asynchronous Clear (aclr)
Deasserts the wrfull signal.
aclr (synchronize with write aclr (synchronize with read
clock) (23) (24)
clock) (25)
The wrfull signal is asserted while the write domain is clearing which nominally takes three cycles of the write clock after the asynchronous release of the aclr input.
The rdempty signal is asserted while the read domain is clearing which nominally takes three cycles of the read clock after the asynchronous release of the aclr input.
Deasserts the rdfull signal.
Asserts the wrempty and rdempty signals.
Resets the wrusedw and rdusedw flags.
Commencement of effects upon assertion
Immediate.
Effects on the q output The output remains unchanged if it is not registered. If the port is registered, it is cleared.
for normal output modes
(26)
Effects on the q output for show-ahead output modes
The output shows 'X' if it is not registered. If the port is registered, it is cleared.
Recovery and Removal Timing Violation Warnings when Compiling a DCFIFO
During compilation of a design that contains a DCFIFO, the Intel Quartus Prime software may issue recovery and removal timing violation warnings.
You may safely ignore warnings that represent transfers from aclr to the read side clock domain. To ensure that the design meets timing, enable the ACLR synchronizer for both read and write domains.
(23) The wrreq signal must be low when the DCFIFO comes out of reset (the instant when the aclr signal is deasserted) at the rising edge of the write clock to avoid a race condition between write and reset. If this condition cannot be guaranteed in your design, the aclr signal needs to be synchronized with the write clock. This can be done by setting the Add circuit to synchronize 'aclr' input with 'wrclk' option from the FIFO parameter editor, or setting the WRITE_ACLR_SYNCH parameter to ON.
(24) Even though the aclr signal is synchronized with the write clock, asserting the aclr signal still affects all the status flags asynchronously.
(25) Even though the aclr signal is synchronized with the read clock, asserting the aclr signal affects all the status flags asynchronously.
(26) For Stratix and Cyclone series, the DCFIFO only supports registered q output in Normal mode, and unregistered q output in Show-ahead mode. For other devices, you have an option to register or unregister the q output (regardless of the Normal mode or Show-ahead mode) in the FIFO parameter editor or set through the ADD_RAM_OUTPUT_REGISTER parameter.
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Note:
To enable the ACLR synchronizer for both read and write domains, on the DCFIFO 2 tab of the FIFO Intel FPGA IP core, turn on Asynchronous clear, Add circuit to synchronize `aclr' input with `wrclk', and Add circuit to synchronize `aclr' input with `rdclk'.
For correct timing analysis, Intel recommends enabling the Removal and Recovery Analysis option in the Timing Analyzer tool when you use the aclr signal. The analysis is turned on by default in the Timing Analyzer tool.
When the Add circuit to synchronize `aclr' input with `wrclk' and Add circuit to synchronize `aclr' input with `rdclk' options are enabled, you can apply the following false path assignment on the reset path:
· set_false_path -to *dcfifo:dcfifo_component| dcfifo_*:auto_generated|dffpipe_*:wraclr|dffe*a[0]
· set_false_path -to *dcfifo:dcfifo_component| dcfifo_*:auto_generated|dffpipe_*:rdaclr|dffe*a[0]
SCFIFO and DCFIFO Show-Ahead Mode
You can set the read request/rdreq signal read access behavior by selecting normal or show-ahead mode.
For normal mode, the FIFO Intel FPGA IP core treats the rdreq port as a normal read request that only performs read operation when the port is asserted.
For show-ahead mode, the FIFO Intel FPGA IP core treats the rdreq port as a readacknowledge that automatically outputs the first word of valid data in the FIFO Intel FPGA IP core (when the empty is low) without asserting the rdreq signal. Asserting the rdreq signal causes the FIFO Intel FPGA IP core to output the next data word, if available.
Figure 5. Normal Mode Waveform
Data appears after the rdreq asserted.
Figure 6.
Show-Ahead Mode Waveform
Data appears before the rdreq asserted.
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Different Input and Output Width
The DCFIFO_MIXED_WIDTHS function supports different write input data and read output data widths if the width ratio is valid. The FIFO parameter editor prompts an error message if the combinations of the input and the output data widths produce an invalid ratio. The supported width ratio in a power of 2 and depends on the RAM.
The IP core supports a wide write port with a narrow read port, and vice versa. The current supported mixed width ratios for Intel Arria 10 and Intel Cyclone 10 GX devices are listed in the following table:
Table 12. Device Family Support for Width Ratios
Device Family Intel Arria 10 Intel Cyclone 10 GX
1, 2, 4, 8, 16, and 32 1, 2, 4, 8, 16, and 32
Valid Width Ratio
Figure 7.
Writing 16-bit Words and Reading 8-bit Words
This figure shows an example of a wide write port (16-bit input) and a narrow read port (8-bit output).
Figure 8.
In this example, the read port is operating at twice the frequency of the write port. Writing two 16-bit words to the FIFO buffer increases the wrusedw flag to two and the rusedw flag to four. Four 8-bit read operations empty the FIFO buffer. The read begins with the least-significant 8 bits from the 16-bit word written followed by the mostsignificant 8 bits.
Writing 8-Bit Words and Reading 16-Bit Words
This figure shows an example of a narrow write port (8-bit input) with a wide read port (16-bit output).
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In this example, the read port is operating at half the frequency of the write port. Writing four 8-bit words to the FIFO buffer increases the wrusedw flag to four and the rusedw flag to two. Two 16-bit read operations empty the FIFO. The first and second 8-bit word written are equivalent to the LSB and MSB of the 16-bit output words, respectively. The rdempty signal stays asserted until enough words are written on the narrow write port to fill an entire word on the wide read port.
DCFIFO Timing Constraint Setting
The FIFO parameter editor provides the timing constraint setting for the DCFIFO function.
Table 13. DCFIFO Timing Constraint Setting Parameter in Intel Quartus Prime Software
Parameter
Generate SDC File and disable embedded timing constraint (27)
Description
Allows you to bypass embedded timing constraints that uses set_false_path in the synchronization registers. A user configurable SDC file is generated automatically when DCFIFO is instantiated from the IP Catalog. New timing constraints consist of set_net_delay, set_max_skew, set_min_delay and set_max_delay are used to constraint the design properly.
Note: Intel recommends that you select this option for high frequency DCFIFO design to achieve timing closure. For more information, refer to User Configurable Timing Constraint on page 22.
Embedded Timing Constraint
When using the Intel Quartus Prime Timing Analyzer with a design that contains a DCFIFO block apply the following false paths to avoid timing failures in the synchronization registers:
· For paths crossing from the write into the read domain, apply a false path assignment between the delayed_wrptr_g and rs_dgwp registers:
set_false_path -from [get_registers {*dcfifo*delayed_wrptr_g[*]}] -to [get_registers {*dcfifo*rs_dgwp*}]
· For paths crossing from the read into the write domain, apply a false path assignment between the rdptr_g and ws_dgrp registers:
set_false_path -from [get_registers {*dcfifo*rdptr_g[*]}] -to [get_registers {*dcfifo*ws_dgrp*}]
The false path assignments are automatically added through the HDL-embedded Synopsis design constraint (SDC) commands when you compile your design. The related message is shown under the Timing Analyzer report.
Note:
The constraints are internally applied but are not written to the Synopsis Design Constraint File (.sdc). To view the embedded-false path, type report_sdc in the console pane of the Timing Analyzer GUI.
(27) Parameter is available in Intel Quartus Prime software version 15.1 and later and applicable for Intel Arria 10 and Intel Cyclone 10 GX devices only. You can disable the embedded timing constraint with QSF setting in prior Intel Quartus Prime versions and other devices. Please refer to KDB link on the QSF assignment setting.
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Note:
If you use the Intel Quartus Prime Timing Analyzer, the false paths are applied automatically for the DCFIFO.
If the DCFIFO is implemented in ALMs, you can ignore the cross-domain timing violations from the data path of the DFFE array (that makes up the memory block) to the q output register. To ensure the q output is valid, sample the output only after the rdempty signal is deasserted.
Related Information The Intel Quartus Prime Timing Analyzer
User Configurable Timing Constraint
DCFIFO contains multi-bit gray-coded asynchronous clock domain crossing (CDC) paths which derives the DCFIFO fill-level. In order for the logic to work correctly, the value of the multi-bit must always be sampled as 1-bit change at a given latching clock edge.
In the physical world, flip-flops do not have the same data and clock path insertion delays. It is important for you to ensure and check the 1-bit change property is properly set. You can confirm this using the Fitter and check using the Timing Analyzer.
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Timing Analyzer will apply the following timing constraints for DCFIFO: · Paths crossing from write into read domain are defined from the
delayed_wrptr_g to rs_dgwp registers. -- set from_node_list [get_keepers $hier_path|dcfifo_component|
auto_generated|delayed_wrptr_g*]
-- set to_node_list [get_keepers $hier_path|dcfifo_component| auto_generated|rs_dgwp|dffpipe*|dffe*]
· Paths crossing from read into write domain are defined from the rdptr_g and ws_dgrp registers. -- set from_node_list [get_keepers $hier_path|dcfifo_component|
auto_generated|*rdptr_g*]
-- set to_node_list [get_keepers $hier_path|dcfifo_component| auto_generated|ws_dgrp|dffpipe*|dffe*]
· For the above paths which cross between write and read domain, the following assignments apply: -- set_max_skew -from $from_node_list -to $to_node_list -get_skew_value_from_clock_period src_clock_period skew_value_multiplier 0.8
-- set_min_delay -from $from_node_list -to $to_node_list -100
-- set_max_delay -from $from_node_list -to $to_node_list 100
-- set_net_delay -from $from_node_list -to $to_node_list -max -get_value_from_clock_period dst_clock_period -value_multiplier 0.8
· The following set_net_delay on cross clock domain nets are for metastability:. -- set from_node_mstable_list [get_keepers $hier_path|dcfifo_component|
auto_generated|ws_dgrp|dffpipe*|dffe*] set to_node_mstable_list [get_keepers $hier_path|dcfifo_component| auto_generated|ws_dgrp|dffpipe*|dffe*]
-- set from_node_mstable_list [get_keepers $hier_path|dcfifo_component| auto_generated|rs_dgwp|dffpipe*|dffe*] set to_node_mstable_list [get_keepers $hier_path|dcfifo_component| auto_generated|rs_dgwp|dffpipe*|dffe*]
-- set_net_delay -from $from_node_list -to $to_node_list -max get_value_from_clock_period dst_clock_period -value_multiplier 0.8
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Timing Analyzer will apply the following timing constraints for mix-width DCFIFO: · Paths crossing from write into read domain are defined from the
delayed_wrptr_g to rs_dgwp registers. -- set from_node_list [get_keepers $hier_path|
dcfifo_mixed_widths_component|auto_generated|delayed_wrptr_g*]
-- set to_node_list [get_keepers $hier_path|dcfifo_mixed_widths_component| auto_generated|rs_dgwp|dffpipe*|dffe*]
· Paths crossing from read into write domain are defined from the rdptr_g and ws_dgrp registers. -- set from_node_list [get_keepers $hier_path|
dcfifo_mixed_widths_component|auto_generated|*rdptr_g*]
-- set to_node_list [get_keepers $hier_path|dcfifo_mixed_widths_component| auto_generated|ws_dgrp|dffpipe*|dffe*]
· For the above paths which cross between write and read domain, the following assignments apply: -- set_max_skew -from $from_node_list -to $to_node_list get_skew_value_from_clock_period src_clock_period skew_value_multiplier 0.8
-- set_min_delay -from $from_node_list -to $to_node_list -100
-- set_max_delay -from $from_node_list -to $to_node_list 100
-- set_net_delay -from $from_node_list -to $to_node_list -max get_value_from_clock_period dst_clock_period -value_multiplier 0.8
· The following set_net_delay on cross clock domain nets are for metastability: -- set from_node_mstable_list [get_keepers $hier_path|
dcfifo_mixed_widths_component|auto_generated|ws_dgrp|dffpipe*|dffe*] set to_node_mstable_list [get_keepers $hier_path| dcfifo_mixed_widths_component|auto_generated|ws_dgrp|dffpipe*|dffe*]
-- set from_node_mstable_list [get_keepers $hier_path| dcfifo_mixed_widths_component|auto_generated|rs_dgwp|dffpipe*|dffe*] set to_node_mstable_list [get_keepers $hier_path| dcfifo_mixed_widths_component|auto_generated|rs_dgwp|dffpipe*|dffe*]
-- set_net_delay -from $from_node_list -to $to_node_list -max get_value_from_clock_period dst_clock_period -value_multiplier 0.8
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SDC Commands
Table 14.
SDC Commands usage in the Intel Quartus Prime Fitter and Timing Analyzer
These SDC descriptions provided are overview for DCFIFO use case. For the exact SDC details, refer to the Intel Quartus Prime Timing Analyzer chapter in the Intel Quartus Prime Pro Edition Handbook.
SDC Command
Fitter
Timing Analyzer
Recommended Settings
set_max_skew
(28)
To constraint placement and routing of flops in the multi-bit CDC paths to meet the specified skew requirement among bits.
To analyze whether the specified skew requirement is fully met. Both clock and data paths are taken into consideration.
Set to less than 1 launch clock.
set_net_delay
Similar to set_max_skew but without taking clock skews into considerations.
To ensure the crossing latency is bounded.
To analyze whether the specified net delay requirement is fully met. Clock paths are not taken into consideration.
This is currently
set to be less than 1 latch clock. (29)
set_min_delay/ set_max_delay
To relax fitter effort by mimicking the
set_false_path command but without overriding other SDCs. (30)
To relax timing analysis for the setup/ hold checks to not fail. (31)
This is currently
set to
100ns/-100ns for max/min. (32)
Related Information The Intel Quartus Prime Timing Analyzer
Coding Example for Manual Instantiation
This section provides a Verilog HDL coding example to create an instance of the DCFIFO. It is not a complete coding for you to compile, but it provides a guideline and some comments for the required structure of the instantiation. You can use the same structure to instantiate other IP cores but only with the ports and parameters that are applicable to the IP cores you instantiated.
Example 1. Verilog HDL Coding Example to Instantiate the DCFIFO
//module declaration module dcfifo8x32 (aclr, data, ...... ,wfull); //Module's port declarations input aclr; input [31:0] data;
(28) It can have significant compilation time impact in older Quartus versions without Timing Analyzer 2.
(29) For advanced users, you can can fine-tune the value based on your design. For instance, if the designs are able to tolerate longer crossing latency (full and empty status will be delayed), this can be relaxed.
(30) Without set_false_path (which has the highest precedence and may result in very long insertion delays), Fitter will attempt to meet the default setup/hold which is extremely over constraint.
(31) Without set_false_path, the CDC paths will be analyzed for default setup/hold, which is extremely over constraint.
(32) Expect an approximately 100ns delay when you observe CDC paths compared to set_false_path.
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. . output wrfull; //Module's data type declarations and assignments wire rdempty_w; . . wire wrfull = wrfull_w; wire [31:0] q = q_w; /*Instantiates dcfifo megafunction. Must declare all the ports available from the megafunction and define the connection to the module's ports. Refer to the ports specification from the user guide for more information about the megafunction's ports*/ //syntax: <megafunction's name> <given an instance name> dcfifo inst1 ( //syntax: .<dcfifo's megafunction's port>(<module's port/wire>) .wrclk (wrclk), .rdclk (rdclk), . . .wrusedw ()); //left the output open if it's not used /*Start with the keyword "defparam", defines the parameters and value assignments. Refer to parameters specifications from the user guide for more information about the megafunction's parameters*/ defparam //syntax: <instance name>.<parameter> = <value> inst1.intended_device_family = "Stratix III", inst1.lpm_numwords = 8, . . inst1.wrsync_delaypipe = 4; endmodule
Design Example
In this design example, the data from the ROM is required to be transferred to the RAM. Assuming the ROM and RAM are driven by non-related clocks, you can use the DCFIFO to transfer the data between the asynchronous clock domains effectively.
Figure 9.
Component Blocks and Signal Interaction
This figure shows the component blocks and their signal interactions.
ROM 256 x 256
Write Control Logic
256
fifo_in
DCFIFO 8 x 256
256
Read
fifo_out Control Logic
RAM 256 x 256
256 rom_out
fifo_wrreq fifo_wrfull
fifo_rdreq fifo_rdempty
256 ram_in 8ram_addr
256 q
8 rom_addr trclk
eccstatus[1:0]
trclk
rvclk
ram_wren
ram_rden
rvclk
rvclk
9 word_count
trclk
Note:
The DCFIFO functions are with ECC feature enabled and implemented using M20K.
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Note:
Both the DCFIFO functions are only capable of handling asynchronous data transferring issues (metastable effects). You must have a controller to govern and monitor the data buffering process between the ROM, DCFIFO, and RAM. This design example provides you the write control logic (write_control_logic.v), and the read control logic (read_control_logic.v) which are compiled with the DCFIFO specifications that control the valid write or read request to or from the DCFIFO.
Note:
This design example is validated with its functional behavior, but without timing analysis and gate-level simulation. The design coding such as the state machine for the write and read controllers may not be optimized. The intention of this design example is to show the use of the IP core, particularly on its control signal in data buffering application, rather than the design coding and verification processes.
To obtain the DCFIFO settings in this design example, refer to the parameter settings from the design file (dcfifo8x32.v).
The following sections include separate simulation waveforms to describe how the write and read control logics generate the control signal with respect to the signal received from the DCFIFO.
Note:
For better understanding, refer to the signal names in the above figure when you go through the descriptions for the simulation waveforms.
Note:
All signals in the following figures and tables have the following numerical format: · Signal values in binary format: reset, trclk, fifo_wrreq, fifo_wrfull · Signal values in HEX format: rom_addr, rom_out, fifo_in
Figure 10. Initial Write Operation to the DCFIFO Function
Table 15. Initial Write Operation to the DCFIFO Function Waveform Description
State
Description
IDLE
Before reaching 10 ns, the reset signal is high and causes the write controller to be in the IDLE state. In the IDLE state, the write controller drives the fifo_wrreq signal to low, and requests the data to be read from rom_addr=00. The ROM is configured to have an unregistered output, so that the rom_out signal immediately shows the data from the rom_addr signal regardless of the reset. This shortens the latency because the rom_out signal is connected directly to the fifo_in signal, which is a registered
continued...
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State WRITE INCADR -
Description
input port in the DCFIFO. In this case, the data (0000000000000000000000000000000000000000000000000000000000000001) is always stable and pending to be written into the DCFIFO when the fifo_wrreq signal is high during the WRITE state.
The write controller transitions from the IDLE state to the WRITE state if the fifo_wrfull signal is low after the reset signal is deasserted. In the WRITE state, the write controller drives the fifo_wrreq signal to high, and requests for write operation to the DCFIFO. The data is encoded through the embedded ECC block in the DCFIFO. The rom_addr signal is unchanged (00) so the data is stable for at least one clock cycle before the DCFIFO actually writes in the data at the next rising clock edge.
The write controller transitions from the WRITE state to the INCADR state, if the rom_addr signal has not yet increased to ff (that is, the last data from the ROM has not been read out). In the INDADR state, the write controller drives the fifo_wrreq signal to low, and increases the rom_addr signal by 1 (00 to 01).
The same state transition continues as stated in IDLE and WRITE states, if the fifo_wrfull signal is low and the rom_addr signal not yet increased to ff.
Figure 11. Initial Read Operation from the DCFIFO Function
Table 16.
State IDLE INCADR
WRITE
--
Initial Read Operation from the DCFIFO Function Waveform Description
Description
Before reaching 35 ns, the read controller is in the IDLE state because the fifo_rdempty signal is high even when the reset signal is low (not shown in the waveform). In the IDLE state, the ram_addr = ff to accommodate the increment of the RAM address in the INCADR state, so that the first data read is stored at ram_addr = 00 in the WRITE state.
The read controller transitions from the IDLE state to the INCADR state, if the fifo_rdempty signal is low. In the INCADR state, the read controller drives the fifo_rdreq signal to high, and requests for read operation from the DCFIFO. The data is decoded and the eccstatus shows the status of the data as no error detected (00), single-bit error detected and corrected(10), or uncorrectable error (11). The ram_addr signal is increased by one (ff to 00), so that the read data can be written into the RAM at ram_addr = 00.
From the INCADR state, the read controller always transition to the WRITE state at the next rising clock edge. In the WRITE state, it drives the ram_wren signal to high, and enables the data writing into the RAM at ram_addr = 00. At the same time, the read controller drives the ram_rden signal to high so that the newly written data is output at q at the next rising clock edge. Also, it increases the word_count signal to 1 to indicate the number of words successfully read from the DCFIFO.
The same state transition continues as stated in INCADR and WRITE states, if the fifo_rdempty signal is low.
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Figure 12. Write Operation when DCFIFO is FULL
Table 17.
State INCADR WAIT
WRITE
--
Write Operation when DCFIFO is FULL Waveform Description
Description
When the write controller is in the INCADR state, and the fifo_wrfull signal is asserted, the write controller transitions to the WAIT state in the next rising clock edge.
In the WAIT state, the write controller holds the rom_addr signal (08) so that the respective data is written into the DCFIFO when the write controller transitions to the WRITE state. The write controller stays in WAIT state if the fifo_wrfull signal is still high. When the fifo_wrfull is low, the write controller always transitions from the WAIT state to the WRITE state at the next rising clock edge.
In the WRITE state, then only the write controller drives the fifo_wrreq signal to high, and requests for write operation to write the data from the previously held address (08) into the DCFIFO. It always transitions to the INCADR state in the next rising clock edge, if the rom_addr signal has not yet increased to ff.
The same state transition continues as stated in INCADR, WAIT, and WRITE states, if the fifo_wrfull signal is high.
Figure 13. Completion of Data Transfer from ROM to DCFIFO
Table 18.
State WRITE
DONE --
Completion of Data Transfer from ROM to DCFIFO Waveform Description
Description
When the write controller is in the WRITE state, and rom_addr = ff, the write controller drives the fifo_wrreq signal to high to request for last write operation to DCFIFO. The data 100 is the last data stored in the ROM to be written into the DCFIFO. In the next rising clock edge, the write controller transitions to the DONE state.
In the DONE state, the write controller drives the fifo_wrreq signal to low.
The fifo_wrfull signal is deasserted because the read controller in the receiving domain continuously performs the read operation. However, the fifo_wrfull signal is only deasserted sometime after the read request from the receiving domain. This is due to the latency in the DCFIFO (rdreq signal to wrfull signal).
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Figure 14. Completion of Data Transfer from DCFIFO to RAM
Note:
The fifo_rdempty signal is asserted to indicate that the DCFIFO is empty. The read controller drives the fifo_rdreq signal to low, and enables the write of the last data 100 at ram_addr =ff. The word_count signal is increased to 256 (in decimal) to indicate that all the 256 words of data from the ROM are successfully transferred to the RAM.
The last data written into the RAM is shown at the q output.
To verify the results, compare the q outputs with the data in rom_initdata.hex file provided in the design example. Open the file in the Intel Quartus Prime software and select the word size as 256 bit. The q output must display the same data as in the file.
Related Information
DCFIFO Design Example Provides all the design files including the testbench. The zip file also includes the .do script (dcfifo_ecc_top.do) that automates functional simulation that you can use to run the simulation using the ModelSim-Intel FPGA Edition software .
Gray-Code Counter Transfer at the Clock Domain Crossing
This section describes the effect of the large skew between gray-code counter bits transfers at the clock domain crossing (CDC) with recommended solution. The graycode counter is 1-bit transition occurs while other bits remain stable when transferring data from the write domain to the read domain and vice versa. If the destination domain latches on the data within the metastable range (violating setup or hold time), only 1 bit is uncertain and destination domain reads the counter value as either an old counter or a new counter. In this case, the DCFIFO still works, as long as the counter sequence is not corrupted.
The following section shows an example of how large skew between the gray-code counter bits can corrupt the counter sequence. Taking a counter width with 3-bit wide and assuming it is transferred from write clock domain to read clock domain. Assume all the counter bits have 0 delay relative to the destination clock, excluding the bit[0] that has delay of 1 clock period of source clock. That is, the skew of the counter bits will be 1 clock period of the source clock when they arrived at the destination registers.
The following shows the correct gray-code counter sequence:
000, 001, 011, 010, 110....
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Note:
which then transfers the data to the read domain, and on to the destination bus registers.
Because of the skew for bit[0], the destination bus registers receive the following sequence:
000, 000, 011, 011, 110....
Because of the skew, a 2-bit transition occurs. This sequence is acceptable if the timing is met. If the 2-bit transition occurs and both bits violate timing, it may result in the counter bus settled at a future or previous counter value, which will corrupt the DCFIFO.
Therefore, the skew must be within a certain skew to ensure that the sequence is not corrupted.
Use the report_max_skew and report_net_delay reports in the Timing Analyzer for timing verification if you use the User Configurable Timing Constraint. For Embedded Timing Constraint, use the skew_report.tcl to analyze the actual skew and required skew in your design.
Related Information
skew_report.tcl
Guidelines for Embedded Memory ECC Feature
The Intel Arria 10 and Intel Cyclone 10 GX FIFO Intel FPGA IP cores support embedded memory ECC for M20K memory blocks. The built-in ECC feature in the Intel Arria 10 and Intel Cyclone 10 GX devices can perform:
· Single-error detection and correction
· Double-adjacent-error detection and correction
· Triple-adjacent-error detection
You can turn on FIFO Embedded ECC feature by enabling enable_ecc parameter in the FIFO Intel FPGA IP GUI.
Note:
Embedded memory ECC feature is only available for M20K memory block type.
Note: Note:
The embedded memory ECC supports variable data width. When ECC is enabled, RAM combines multiple M20K blocks in the configuration of 32 (width) x 512 (depth) to fulfill your instantiation. The unused data width will be tied to the VCC internally.
The embedded memory ECC feature is not supported in mixed-width mode.
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Figure 15. ECC Option in FIFO Intel FPGA IP GUI
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When you enable the ECC feature, a 2-bit wide error correction status port (eccstatus[1:0]) will be created in the generated FIFO entity. These status bits indicate whether the data that is read from the memory has an error in single-bit with correction, fatal error with no correction, or no error bit. · 00: No error · 01: Illegal · 10: A correctable error occurred and the error has been corrected at the outputs;
however, the memory array has not been updated. · 11: An uncorrectable error occurred and uncorrectable data appears at the output
Related Information Error Correction Code in Embedded Memory User Guide
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If an IP core version is not listed, the user guide for the previous IP core version applies.
IP Core Version
User Guide
17.1
SCFIFO and DCFIFO IP Cores User Guide
17.0
SCFIFO and DCFIFO IP Cores User Guide
16.0
SCFIFO and DCFIFO IP Cores User Guide
15.1
SCFIFO and DCFIFO IP Cores User Guide
14.1
SCFIFO and DCFIFO IP Cores User Guide
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Document Revision History for the FIFO Intel FPGA IP User Guide
Document Version 2020.12.14 2019.11.21
2018.09.24
2018.08.01 2018.07.02 2018.05.07
Intel Quartus Prime Version
18.0 18.0
18.0
18.0 18.0
18.0
Changes
Updated the description in the Gray-Code Counter Transfer at the Clock Domain Crossing topic of the FIFO section.
· Added lpm_hint to Table: FIFO Parameters. · Updated the description in the Recovery and Removal Timing Violation
Warnings when Compiling a DCFIFO section. · Remove references to Intel Stratix 10 devices throughout the
document. Refer to the FIFO Intel FPGA IP section of the Intel Stratix 10 Embedded Memory User Guide for more information.
· Updated Table: Input and Output Ports Description to include a note for usedw, wrusedw, and rdusedw ports.
· Updated Table: FIFO Parameters to update the footnotes for lpm_widthu_r, delay_wrusedw, read_aclr_synch, and almost_empty_value.
Updated the DCFIFO Timing Constraint Setting topic to add a note to recommend selecting the Generate SDC File and disable embedded timing constraint option for high frequency DCFIFO design.
Updated the VHDL LIBRARY-USE Declaration topic to correct the VHDL Library declaration example from USE altera_mf_altera_mf_components.all; to USE altera_mf.altera_mf_components.all;.
· Renamed the document as FIFO Intel FPGA IP User Guide. · Renamed "SCFIFO and DCFIFO" IP cores to "FIFO Intel FPGA IP" core
as per Intel rebranding. · Updated the description for ram_block_type in the FIFO Parameters
topic. · Updated Table: Device Family Support for Width Ratios to include valid
width ratios for Intel Stratix 10 devices. · Added a note to FIFO Synchronous Clear and Asynchronous Clear Effect
topic to clarify that for Intel Stratix 10 devices, asserting aclr or sclr upon power-up guarantee correct functionality. · Updated the note in Table: DCFIFO Timing Constraint Setting Parameter in Intel Quartus Prime Software. · Updated Guidelines for Embedded Memory ECC Feature topic. · Updated Figure: ECC Option in FIFO Intel FPGA IP GUI. · Updated for latest branding standards. · Made editorial updates throughout the document.
Date November 2017
May 2017
Version 2017.11.06
2017.05.08
Changes
· Added support for Intel Stratix 10, Intel Cyclone 10 LP, and Intel Cyclone 10 GX devices.
· Updated the LE Implemented RAM Mode for SCFIFO and DCFIFO table to correct output latency for wrreq to empty.
· Updated the SCFIFO and DCFIFO Parameters to include add_usedw_msb_bit register signal.
· Updated for latest branding standards.
· Rebranded as Intel. · Added a table listing the device family support for width ratio in
the Different Input and Output Width topic. · Minor typographical corrections and stylistic changes.
continued...
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Date August 2016 May 2016 May 2016
November 2015
December 2014
May 2013 August 2012 August 2012
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Version 2016.08.29 2016.05.30 2016.05.02
2015.11.02
2014.12.17
8.2 8.1 8.0
Changes
· Added note to Configuration Methods stating that scfifo and dcfifo cannot ne used for FIFO Qsys entity name.
· Added note to almost_empty in SCFIFO and DCFIFO Signals table.
· Added SCFIFO ALMOST_EMPTY Functional Timing section.
Added note about using skew_report.tcl if Embedded Timing Constraint is used and report_max_skew.
· Added list of user configurable constraint commands and descriptions in Constrain Commands.
· Added timing constraints for mixed-width DCFIFO. · Upgraded design example with ECC feature enabled. · Added Guidelines for Embedded Memory ECC Feature section. · Removed 32-bit width FIFO limitation for eccstatus signal and
enable_ecc paramenter.. · Added FIFO IP core parameter editor directory in IP catalog in
Configuration Methods section.
· Added User Configurable Timing Constraint. · Added DCFIFO Timing Constraint Setting. · Renamed Constraint Settings to Embedded Constraint Settings. · Moved normal and show-ahead description from parameter table
to SCFIFO and DCFIFO Show-Ahead Mode subsection. · Added normal and show-ahead waveform for comparison. · Added eccstatus port in block diagram and port table list
available in Quartus II 15.1 release. · Added enable_ecc parameter in SCFIFO and DCFIFO
Parameters. · Updated Verilog HDL prototype directory. · Corrected lpm_numwords register equation. · Updated Example 1: Verilog HDL Coding Example to Instantiate
the DCFIFO IP Core.
· Clarified that there are no minimum number of clock cycles for aclr signals that must remain active.
· Added Recovery and Removal Timing Violation Warnings when Compiling a DCFIFO Megafunction section.
· Removed a note about ignoring any recovery and removal violation reported in the TimeQuest timing analyzer that represent transfers from the aclr to the read side clock domain in Synchronous Clear and Asynchronous Clear Effect section.
· Updated Table 8 on page 20 to state that both the read and write pointers reset to zero upon assertion of either the sclr or aclr signal.
· Updated Table 1 on page 7 to note that the wrusedw, rdusedw, wrfull, rdfull wrempty and rdempty values are subject to the latencies listed in Table 5 on page 18.
· Included a link to skew_report.tcl "Gray-Code Counter Transfer at the Clock Domain Crossing" on page 29.
· Updated "DCFIFO" on page 3, "Ports Specifications" on page 6, "Functional Timing Requirements" on page 14, "Synchronous Clear and Asynchronous Clear Effect" on page 20.
· Updated Table 1 on page 7, Table 2 on page 10, Table 9 on page 21.
· Added Table 4 on page 16. · Renamed and updated "DCFIFO Clock Domain Crossing Timing
Violation" to "Gray-Code Counter Transfer at the Clock Domain Crossing" on page 29.
continued...
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Date February 2012 September 2010 January 2010 September 2009
February 2009 January 2009 May 2007
March 2007 September 2005
Version 7.0 6.2 6.1 6.0
5.1 5.0 4.0
3.3 3.2
Changes
· Updated the notes for Table 4 on page 16. · Added the "DCFIFO Clock Domain Crossing Timing Violation"
section.
Added prototype and component declarations.
· Updated "Functional Timing Requirements" section. · Minor changes to the text.
· Replaced "FIFO Megafunction Features" section with "Configuration Methods".
· Updated "Input and Output Ports". · Added "Parameter Specifications", "Output Status Flags and
Latency", "Metastability Protection and Related Options", "Constraint Settings", "Coding Example for Manual Instantiation", and "Design Example".
Minor update in Table 8 on page 17.
Complete re-write of the user guide.
· Added support for Arria GX devices. · Updated for new GUI. · Added six design examples in place of functional description. · Reorganized and updated Chapter 3 to have separate tables for
the SCFIFO and DCFIFO megafunctions. · Added Referenced Documents section.
· Minor content changes, including adding Stratix III and Cyclone III information
· Re-took screenshots for software version 7.0
Minor content changes.
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