匯編-簡單的鎖定/解鎖程序錯誤

Question

我編寫的程序有一個錯誤，我不明白為什么。 應該在用戶按下任意鍵后將狀態設置為鎖定/解鎖，並提供一些反饋。 但是經過兩個周期后，輸出出錯。 例：

The door is locked Press any key to unlock The door is unlocked Press any key to lock The door is locked q The door is unlocked q The door is locked q The door is unlocked q

q是我按下的按鈕。

這是代碼。 我將不勝感激任何幫助。

## program for a simple door locking device
## register use:    $v0: stores syscall code
##                  $a0: stores entered number
##                  $s0: stores status number

.data
    locked:     .asciiz "The door is locked\n"
    unlocked:   .asciiz "The door is unlocked\n"
    unlock:     .asciiz "Press any key to unlock\n"
    lock:       .asciiz "Press any key to lock\n"

.text
.globl main

main:

# store default status value
ori $s0, $0, 1      # store the default 1

# output the status
li $v0, 4           # system call code for print_str
la $a0, locked      # print "The door is locked"
syscall

loop: 

bgtz $s0, unlocking     # if $s0 > 0, start unlocking
beq $s0, $0, locking    # if $s0 = 0, start locking

unlocking:  

# output the user instruction
li $v0, 4               # system call code for print_str
la $a0, unlock          # print "Press any key to unlock"
syscall

# ask for input
li $v0, 8               # system call code for read_str
syscall

# set status to unlocked (0)
ori $s0, $0, 0      

# output new status
li $v0, 4               # system call code for print_str
la $a0, unlocked        # print "The door is unlocked"
syscall

j loop  

locking:

# output the user instruction
li $v0, 4               # system call code for print_str
la $a0, lock            # print "Press any key to lock"
syscall

# ask for input
li $v0, 8 # system call code for read_str
syscall

# set status to locked (1)
ori $s0, $0, 1  

# output new status
li $v0, 4           # system call code for print_str
la $a0, locked      # print "The door is locked"
syscall     

j loop  

Answer 1

調用read_str您需要將a0設置為指向虛擬輸入緩沖區，否則您將覆蓋恰好指向的a0。 您還需要將a1設置為要讀取的字符數。

請注意，僅讀取單個字符的syscall 12可能是更好的選擇。

請參閱syscall列表 。