关于实验16的测试代码执行问题
本帖最后由 laocaiye 于 2025-3-21 15:12 编辑按照小鱼老师提供的实验16的安装程序（二）（里面的dx和di的错误点也更正了），在进行测试时，第一次执行可以出现应有的效果。但是存在以下问题：
一是中断程序只能执行一次，执行效果出现后就会定屏（一直显示），也无法正常退出DOS界面，只能强制点X关闭界面。
二是在问题一的基础上，后续设置的中断测试代码，根本就不执行。
三是同样的测试代码exe，在上次强制关闭后，在进入调试，就不在出现效果界面。
以下是测试代码
assume cs:code
code segment
start: mov ax,0b800h
mov es,ax
mov di,0
mov ax,102h
int 7ch
mov cx,25；只执行本段红色代码部分
s0: push cx
s01: mov cx,80
mov byte ptr es:,'0'
add di,2
loop s01
pop cx
loop s0
call delay
mov ax,204h；蓝色测试代码不执行
int 7ch
mov ax,4c00h
int 21h
delay: push dx
push ax
mov dx,10h
mov ax,0
s1: sub ax,1
sbb dx,0
cmp ax,0
jne s1
cmp dx,0
jne s1
pop ax
pop dx
ret
code ends
end start 你的问题可能与以下几个方面有关：
1. **中断处理程序未正确返回**
你的代码调用 `int 7ch` 之后，可能没有正确返回，导致程序停滞。你可以检查 `int 7ch` 对应的中断处理程序是否正确执行 `iret` 返回。
2. **中断 7Ch 可能未正确注册**
你调用 `mov ax, 102h` 和 `mov ax, 204h` 进行中断调用，但如果 `int 7ch` 处理程序没有正确安装，可能会导致后续代码无法执行。
3. **DOS 环境下的调试问题**
强制关闭 DOS 窗口后，可能会导致中断向量表未恢复，影响后续的测试。建议在程序退出时，确保恢复原始的中断向量。
### 解决方案：
- **确保 `int 7ch` 处理程序正确安装**，并在 `iret` 之前正确保存和恢复寄存器。
- **在程序退出时恢复原始中断**，避免影响后续测试。
- **使用 `debug` 或 `TD`（Turbo Debugger）检查 `int 7ch` 的执行情况**，看看是否正确返回。
如果你能提供 `int 7ch` 具体的中断处理代码，我可以帮你进一步分析。
以上回复来自 FishC AI 小助理，如未能正确解答您的问题，请继续追问。 以下是安装程序
assume cs:code
code segment
setbegin: jmp short getid
table dw sub1,sub2,sub3,sub4
getid: push bx
cmp ah,3
ja iretp
mov bh,0
mov bl,ah
add bx,bx
call word ptr table
iretp: pop bx
iret
sub1: push es
push cx
push bx
mov bx,0b800h
mov es,bx
mov bx,0
mov cx,2000
lpcls: mov byte ptr es:,' '
add bx,2
loop lpcls
pop bx
pop cx
pop es
ret
sub2: push es
push cx
push bx
mov bx,0b800h
mov es,bx
mov bx,1
mov cx,2000
lpfore: and byte ptr es:,11111000b
or es:,al
add bx,2
loop lpfore
pop bx
pop cx
pop es
ret
sub3: push es
push cx
push bx
mov cl,4
shl al,cl
mov bx,0b800h
mov es,bx
mov bx,1
mov cx,2000
lpbgd: and byte ptr es:,10001111b
or es:,al
add bx,2
loop lpbgd
pop bx
pop cx
pop es
ret
sub4: push es
push cx
push ds
push di
push si
mov dx,0b800h
mov es,dx
mov ds,dx
mov di,0
mov si,160
mov cx,24
cld
lpscr: push cx
mov cx,160
rep movsb
pop cx
loop lpscr
mov cx,80
mov di,160*24
clsr: mov byte ptr es:,' '
add di,2
loop clsr
pop si
pop di
pop ds
pop cx
pop es
ret
setend: nop
start: mov ax,cs
mov ds,ax
mov ax,0
mov es,ax
mov di,200h
mov si,offset setbegin
mov cx,offset setend - offset setbegin
cld
rep movsb
cli
mov word ptr es:,0
mov word ptr es:,20h
sti
mov ax,4c00h
int 21h
code ends
end start laocaiye 发表于 2025-03-21 15:05
以下是安装程序
assume cs:code
code segment
...
It looks like you're implementing a custom interrupt handler at `int 7Ch`, but you're encountering issues where the interrupt only executes once, the screen freezes, and subsequent executions do not work. Let's analyze the potential causes and solutions.
---
### **Potential Issues**
1. **Interrupt Handler Not Properly Installed**
- Your installation code copies the interrupt handler to `0:200h`, but it does not properly set the interrupt vector for `int 7Ch`. Instead, it modifies `es:` and `es:`, which are likely affecting `int 00h` (Divide by Zero Exception) instead of `int 7Ch`.
2. **Interrupt Handler Not Returning Properly**
- The handler should end with `iret`, which it does in `iret` at `iret: pop bx iret`. However, if the interrupt is not properly installed, it may not be executing at all.
3. **Interrupt Handler Overwriting Memory**
- The handler modifies video memory (`0xB8000`), but if `di` is not properly managed, it could be writing outside the intended range.
4. **Interrupt Vector Not Restored**
- If the program is forcefully closed, the interrupt vector remains pointing to an invalid memory location, causing subsequent executions to fail.
---
### **Suggested Fixes**
#### **1. Properly Set the Interrupt Vector**
Modify your installation code to correctly set `int 7Ch` in the interrupt vector table:
mov ax, 0
mov es, ax
mov word ptr es:, 200h; Offset of handler
mov word ptr es:, 0 ; Segment of handler
This ensures that `int 7Ch` correctly points to your handler.
#### **2. Ensure the Handler Returns Properly**
Your handler should always end with `iret` to return control to the calling program.
#### **3. Restore the Original Interrupt Vector on Exit**
Before exiting, restore the original interrupt vector to prevent issues in subsequent runs.
---
### **Next Steps**
- Try modifying your installation code to correctly set `int 7Ch`.
- If the issue persists, use a debugger (`debug.exe` or `TD`) to inspect the interrupt vector at `int 7Ch` (`d 0:7C*4`).
- If you still encounter issues, let me know what happens when you run `int 7Ch` manually in a debugger.
Would you like me to provide a corrected version of your installation code?
以上回复来自 FishC AI 小助理，如未能正确解答您的问题，请继续追问。 看样子老头子还要先学习英语，算了。
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