1. ECE 0142
Recitation #5

2. SPIM Simulator Official website: Versions
Versions
Unix, Linux, Mac: spim, xspim
Windows: PCSpim

3. Register Pane Program Pane Memory & stack Program input/output
Memory address of instructions
Instructions
Correspondent line in source file
Program Pane
Encoded instruction
Memory & stack
Program input/output
Message Pane

4. SPIM Basics Must have a label “main” – entrance of your program
Data segment
Starts with “.data” directive
Memory locations, constants, string literals
Text segment
Your program

5. System Calls Simple I/O functions in your program Example How to use?
print_int: print an integer on console
print_string: print a zero-ended string on console
read_int
......
How to use?
Load $v0 with service number (e.g. 1 for print_int)
Load arguments (if any) to $a0, $a1 or $f12
syscall

6. Example: Swap Words
.data value1: .word 1111 value2: .word 2222 msg_v1: .asciiz "v1=" msg_v2: .asciiz "v2=" newline: .asciiz "\n"
.text .globl main main: # Load value1, value2 into $s0, $s1 la $t0, value1 lw $s0, 0($t0) la $t1, value2 lw $s1, 0($t1) # swap $s0, $s1 move $s2, $s0 move $s0, $s1 move $s1, $s2 # Save $s0, $s1 back to value1, value2 sw $s0, 0($t0) sw $s1, 0($t1)

7. Example (cont.)
# print value1 li $v0, 4 la $a0, msg_v1 syscall li $v0, 1 la $t0, value1 lw $a0, 0($t0) la $a0, newline
# print value2 li $v0, 4 la $a0, msg_v2 syscall li $v0, 1 la $t0, value2 lw $a0, 0($t0) la $a0, newline # exit li $v0, 10