SPIM : A MIPS Simulator

1. SPIM : A MIPS Simulator Archi & Net Lab 이용석 (yslee@archi.snu.ac.kr)

2. Contents • Introduction • SPIM Interface • Simulator Usage • MIPS R2000 Assembler Language • Program Example

3. Introduction (1/2) • What’s SPIM? • A simulator that runs programs for the MIPS R2000/R3000 RISC computers • What does SPIM do? • Reads and executes MIPS assembly language file immediately • Works as a debugger • Provides some OS like services

4. Introduction (2/2) • Where can we get SPIM? • FTP: ftp.cs.wisc.edu • /pub/spim/spimwin.exe • Installing SPIM • Just run spimwin.exe and follow the installation procedure

5. Windows Interface • Registers window • shows the values of all registers in the MIPS CPU and FPU • Text segment window • shows instructions • Data segment window • shows the data loaded into the program’s memory and the data of the program’s stack • Messages window • shows PCSpim messages (include error messages)

6. Simulator Usage • Opening source file • Use File menu or toolbar button • Simulation • Go: Run loaded program • Break: Stop the execution of the program • Single / Multiple Step: Stepping for debugging • Breakpoint: Stop program before it executes a particular instruction • Reload: Reload source file after change it with editor program

7. MIPS Assembly Layout • Program Layout .text #code section .globl main #starting point: must be global main: # user program code .data #data section label: .data_type list_of_data #data loc + data type + data .text #code section label: #function label #user functions

8. MIPS Assembler Directives (1/2) • Data Types • .word, .half - 32/16 bit integer • .byte - 8 bit integer (similar to ‘char’ type in C) • .ascii, .asciiz - string (asciiz is null terminated) • Strings are enclosed in double-quotas(”) • Special characters in strings follow the C convention • newline(\n), tab(\t), quote(\”) • .double, .float - floating point

9. MIPS Assembler Directives (2/2) • Other Directives • .text - Indicates that following items are stored in the user text segment • .data - Indicates that following data items are stored in the data segment • .globlsym- Declare that symbol sym is global and can be referenced from other files

10. SPIM System Calls • System Calls (syscall) • OS-like services • Method • Load system call code into register $v0 • Load arguments into registers $a0…$a3 • After call, return value is in register $v0 • Frequently used system calls

11. SPIM Program Example (1/3) • A Simple Program #sample example 'add two numbers’ .text # text section .globl main # call main by SPIM main: la $t0, value # load address ‘value’ into $t0 lw $t1, 0($t0) # load word 0(value) into $t1 lw $t2, 4($t0) # load word 4(value) into $t2 add $t3, $t1, $t2 # add two numbers into $t3 sw $t3, 8($t0) # store word $t3 into 8($t0) .data # data section value: .word 10, 20, 0 # data for addition

12. SPIM Program Example (2/3) • A Program with System Call #sample example 'system call' .text .globl main main: la $t0, value li $v0, 5 syscall sw $v0, 0($t0) li $v0, 5 syscall sw $v0, 4($t0) lw $t1, 0($t0) lw $t2, 4($t0) add $t3, $t1, $t2 sw $t3, 8($t0) li $v0, 4 la $a0, msg1 syscall li $v0, 1 move $a0, $t3 syscall .data value: .word 0, 0, 0 msg1: .asciiz "Result = "

13. SPIM Program Example (3/3) • A Program with Procedure Call # swap(int v[], int k) # { # int temp; # temp = v[k]; # v[k] = v[k+1]; # v[k+1] = temp; # } swap: add $t1, $a1, $a1 add $t1, $t1, $t1 add $t1, $a0, $t1 lw $t0, 0($t1) lw $t2, 4($t1) sw $t2, 0($t1) sw $t0, 4($t1) jr $ra # sample example ‘swap two numbers’ .text .globl main main: la $a0, array addi $a1, $0, 0 addi $sp, $sp, -4 sw $ra, 0($sp) jal swap lw $ra, 0($sp) addi $sp, $sp, 4 jr $ra .data array: .word 5, 4, 3, 2, 1