5.18. Jal, Jr Subroutine Instructions
User Manual:
Open the PDF directly: View PDF 
.
Page Count: 9
| Download | |
| Open PDF In Browser | View PDF |
1/3/2019 5.18. jal, jr: Subroutine instructions 5.18 jal, jr: Subroutine instructions A brief note from your instructor: Sections 5.18-5.21 provide a good conceptual description of how MIPS subroutines work, using temporary registers ($t) and parameters. However, practically speaking their translation is not accurate because temporary registers by de nition saved across procedure calls, and MIPS provides $a registers for parameters. Therefore I recommend skimming this section but will not require completing the activities. I will be demonstrating in cla way of translating subroutines to MIPS, using these concepts. Subroutines A program often needs to perform the same operation for different data values. Ex: Determining the maximum of two value temperature from Fahrenheit to Celsius, etc. Instead of duplicating the instruction sequence for an operation multiple times can use a subroutine. A subroutine is a sequence of instructions that performs a speci c operation that can be called from a program. A subroutine call causes the subroutine's statements to execute. PARTICIPATION ACTIVITY Start 5.18.1: Subroutine for computing maximum of two values. 2x speed # Compute max of DM[5000] & DM[5004] addi $t6, $zero, 5000 lw $t0, 0($t6) addi $t6, $zero, 5004 lw $t1, 0($t6) https://learn.zybooks.com/zybook/FIUCDA3103CickovskiFall2018/chapter/5/section/18 # Compute max of DM[5000] & DM[5004] addi $t6, $zero, 5000 lw $t0, 0($t6) addi $t6, $zero, 5004 lw $t1, 0($t6) 1/9 1/3/2019 5.18. jal, jr: Subroutine instructions slt $t3, $t0, $t1 bne $t3, $zero, Max1IsT1 add $t2, $zero, $t0 j Max1End Max1IsT1: add $t2, $zero, $t1 Max1End: addi $t6, $zero, 5008 sw $t2, 0($t6) # Compute max of DM[5012] & DM[5016] addi $t6, $zero, 5012 lw $t0, 0($t6) addi $t6, $zero, 5016 lw $t1, 0($t6) slt $t3, $t0, $t1 bne $t3, $zero, Max2IsT1 add $t2, $zero, $t0 j Max2End Max2IsT1: add $t2, $zero, $t1 Max2End: addi $t6, $zero, 5020 sw $t2, 0($t6) No subroutine with redundant code PARTICIPATION ACTIVITY Call CompMax subroutine (not shown) addi $t6, $zero, 5008 sw $t2, 0($t6) # Compute max of DM[5012] & DM[5016] addi $t6, $zero, 5012 lw $t0, 0($t6) addi $t6, $zero, 5016 lw $t1, 0($t6) Call CompMax subroutine (not shown) addi $t6, $zero, 5020 sw $t2, 0($t6) ... CompMax: slt $t3, $t0, $t1 bne $t3, $zero, MaxIsT1 add $t2, $zero, $t0 j MaxEnd MaxIsT1: add $t2, $zero, $t1 MaxEnd: Return from subroutine CompMax subroutine computes max of $t0 and $t1, writing max to $t2. 5.18.2: Subroutines. Refer to the animation above. 1) What label indicates the rst instruction of the subroutine for computing the maximum value? CompMax MaxEnd https://learn.zybooks.com/zybook/FIUCDA3103CickovskiFall2018/chapter/5/section/18 2/9 1/3/2019 5.18. jal, jr: Subroutine instructions 2) How many redundant instructions in the original code were moved to the subroutine. 5 10 3) A subroutine's instructions must be duplicated each time the subroutine is called. True False 4) A subroutine may have up to 1024 instructions. True False Jump and link and jump register instructions The jump and link (jal) instruction stores the address of the next instruction in register $ra, and then jumps to the instructio speci ed location. Ex: jal CalcCube stores the address of the instruction after the jal instruction in $ra, and continues exe instruction at CalcCube; CalcCube is the label for the rst instruction of the subroutine. The $ra register (or return address r the instruction address to which a subroutine returns after executing. The jump register (jr) instruction jumps to the instruc address held in a register. Ex: jr $ra jumps to the instruction at the address held in register $ra. A programmer uses jal to subroutine, and jr to return from a subroutine. PARTICIPATION ACTIVITY Start 5.18.3: Subroutine call using jal and jr instructions. 2x speed https://learn.zybooks.com/zybook/FIUCDA3103CickovskiFall2018/chapter/5/section/18 3/9 1/3/2019 5.18. jal, jr: Subroutine instructions # Compute cube of 3 12 addi $t0, $zero, 3 # Call CalcCube 16 jal CalcCube sw $t1, 0($t6) 20 Register file $zero 0 5000 $t0 3 5004 $t1 ... # CalcCube subroutine CalcCube: mul $t1, $t0, $t0 60 mul $t1, $t1, $t0 64 jr $ra 68 PARTICIPATION ACTIVITY Data memory DM 9 27 27 ... $t6 5000 $ra 20 5.18.4: jal and jr instructions. 1) Write a jump and link instruction to call a subroutine named CalcTip. Check Show answer 2) If the jal instruction below is located in instruction memory at address 200, what value is written to register $ra? jal DetSpeed Check Show answer https://learn.zybooks.com/zybook/FIUCDA3103CickovskiFall2018/chapter/5/section/18 4/9 1/3/2019 5.18. jal, jr: Subroutine instructions 3) Using the $ra register, write an instruction to return from a subroutine named CalcTip. Check Show answer 4) Assume $ra holds 116. If the jr instruction below is located in instruction memory at address 200, what is the address of the instruction executed after jr $ra? Check Show answer Arguments and return values An argument is a value passed to a subroutine, that in uences the subroutine's operations. A return value is a value returne subroutine. A simple subroutine may use speci c registers for the argument and return value. Ex: The CalcCube subroutine for the subroutine's argument and $t1 for the return value. The assembly program below passes arguments to the CalcCube subroutine using $t0. The CalcCube subroutine returns t $t1. The program rst passes 3 to the subroutine by writing 3 to register $t0. After executing the subroutine, $t1 holds the v stored in data memory at address 5000. The program then passes 17 to the subroutine by writing 17 to $t0. The result of 4 stored to data memory at address 5004. Figure 5.18.1: Passing arguments to multiple CalcCube subroutine calls. https://learn.zybooks.com/zybook/FIUCDA3103CickovskiFall2018/chapter/5/section/18 5/9 1/3/2019 5.18. jal, jr: Subroutine instructions # Initialize registers for DM addresses addi $t5, $zero, 5000 addi $t6, $zero, 5004 # Compute cube of 3 addi $t0, $zero, 3 # Pass argument of 3 jal CalcCube # Call CalcCube sw $t1, 0($t5) # Store result to DM[5000] # Compute cube of 17 addi $t0, $zero, 17 # Pass argument of 17 jal CalcCube # Call CalcCube sw $t1, 0($t6) # Store result to DM[5004] j Done # CalcCube subroutine. # $t0 is subroutine argument # $t1 is subroutine return value CalcCube: mul $t1, $t0, $t0 mul $t1, $t1, $t0 jr $ra # Return from subroutine Done: PARTICIPATION ACTIVITY 5.18.5: Subroutine arguments and return values. The CalcEq subroutine below evaluates the equation: x * (y - z). Values for x, y, and z are passed to the subroutine as arguments. CalcEq: sub $t5, $t1, $t2 mul $t3, $t5, $t0 jr $ra 1) Which register is used for x? https://learn.zybooks.com/zybook/FIUCDA3103CickovskiFall2018/chapter/5/section/18 6/9 1/3/2019 5.18. jal, jr: Subroutine instructions $t0 $t1 $t2 2) Which register is used for the argument y? $t0 $t1 $t2 3) Which register is used for the argument z? $t2 $t3 4) Which register is used for the return value? $ra $t3 PARTICIPATION ACTIVITY 5.18.6: Create a subroutine. Using the CompMax subroutine, complete the assembly program to compute the maximum of the three values in DM[5000], DM[5004], and DM[5008], storing the result in DM[5020]. 1. Load $t0 and $t1 with DM[5000] and DM[5004], and call the CompMax subroutine. 2. Copy the result, which is held in $t2, into $t0. Load $t1 with DM[5008]. Call the CompMax subroutine. 3. Store the result, which is held in $t2, to DM[5020] https://learn.zybooks.com/zybook/FIUCDA3103CickovskiFall2018/chapter/5/section/18 7/9 1/3/2019 5.18. jal, jr: Subroutine instructions Assembly Line 1 Line 2 Line 3 Line 4 Line 5 Line 6 Line 7 Line 8 Line 9 Line 10 Line 11 Line 12 Line 13 # FIXME: Compute maximum of DM[5000], # DM[5004], and DM[5008] j Done $zero Registers 0 5000 $t0 0 5004 $t1 0 5008 $t2 0 5020 $t3 0 + $t4 0 $t5 0 $t6 0 CompMax: slt $t3, $t0, $t1 bne $t3, $zero, MaxIsT1 add $t2, $zero, $t0 j MaxEnd MaxIsT1: add $t2, $zero, $t1 MaxEnd: jr $ra Done: Da + ENTER SIMULATION STEP RUN More options Table 5.18.1: Instruction summary: jal, jr. Instruction Format Description jal jal JLabel Jump and link: Stores the address of the next instruction in register $ra, and continues execution with the instruction at JLabel. jr jr $a Jump register: Causes execution to continue with the instruction at address $a. Example jal CalcTip jr $t3 CHALLENGE https://learn.zybooks.com/zybook/FIUCDA3103CickovskiFall2018/chapter/5/section/18 8/9 1/3/2019 5.18. jal, jr: Subroutine instructions ACTIVITY 5.18.1: Call and create subroutines. Start 1 Pass DM[$t3] to the YearlySalary subroutine, and store the return value to DM[$t4]. $t1 is the subroutine argument. $t2 is the subroutine return value. lw $t1 , 0( $t1 ) lw $t1 , 0( $t1 ) lw $t1 , 0( $t1 ) $t3 lw $t1 , 0( $t1 ) $t4 $t2 , $zero , 2000 mul $t2 , $t1 , $t2 jr $ra YearlySalary: addi $t1 $t2 Registers 0 0 5000 5004 2 5 5 Done: 1 Check 2 Next Provide feedback on this section https://learn.zybooks.com/zybook/FIUCDA3103CickovskiFall2018/chapter/5/section/18 9/9
Source Exif Data:
File Type : PDF File Type Extension : pdf MIME Type : application/pdf PDF Version : 1.4 Linearized : No Page Count : 9 Creator : Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/71.0.3578.98 Safari/537.36 Producer : Skia/PDF m71 Create Date : 2019:01:03 18:29:34+00:00 Modify Date : 2019:01:03 18:29:34+00:00EXIF Metadata provided by EXIF.tools