编程中DSP程序中断中使用XF管脚误区问题

sick

在5509 DSP程序中断中使用XF管脚
使一个LED的闪亮是经常用的，但这其中有一个误区，现分析如下，以定时器控制LED灯为例：

1. <span style="color: rgb(51, 51, 51); font-family: " microsoft="" yahei";"="">void main()</span>
   
2. <span style="color: rgb(51, 51, 51); font-family: " microsoft="" yahei";"="">   {</span>
   
3. <span style="color: rgb(51, 51, 51); font-family: " microsoft="" yahei";"="">    init_5509();</span>
   
4. <span style="color: rgb(51, 51, 51); font-family: " microsoft="" yahei";"="">    init_timer();</span>
   
5. <span style="color: rgb(51, 51, 51); font-family: " microsoft="" yahei";"="">    while(1) </span>
   
6. <span style="color: rgb(51, 51, 51); font-family: " microsoft="" yahei";"="">         {</span>
   
7. <span style="color: rgb(51, 51, 51); font-family: " microsoft="" yahei";"="">         asm(" NOP");</span>
   
8. <span style="color: rgb(51, 51, 51); font-family: " microsoft="" yahei";"="">         }</span>
   
9. <span style="color: rgb(51, 51, 51); font-family: " microsoft="" yahei";"="">   }</span>
   
10. 
    
11. 
    
12. <span style="color: rgb(51, 51, 51); font-family: " microsoft="" yahei";"="">interrupt void int_timer0()</span>
    
13. <span style="color: rgb(51, 51, 51); font-family: " microsoft="" yahei";"="">{</span>
    
14. <span style="color: rgb(51, 51, 51); font-family: " microsoft="" yahei";"="">         Flag=Flag+1;</span>
    
15. <span style="color: rgb(51, 51, 51); font-family: " microsoft="" yahei";"="">         if   (Flag>10)</span>
    
16. 
    
17. 
    
18. <span style="color: rgb(51, 51, 51); font-family: " microsoft="" yahei";"="">              asm(" SSBX XF");</span>
    
19. 
    
20. 
    
21. <span style="color: rgb(51, 51, 51); font-family: " microsoft="" yahei";"="">         else</span>
    
22. 
    
23. 
    
24. <span style="color: rgb(51, 51, 51); font-family: " microsoft="" yahei";"="">              asm(" RSBX XF");</span>
    
25. <span style="color: rgb(51, 51, 51); font-family: " microsoft="" yahei";"="">         if (Flag>20)</span>
    
26. 
    
27. 
    
28. <span style="color: rgb(51, 51, 51); font-family: " microsoft="" yahei";"="">               Flag=0;</span>
    
29. <span style="color: rgb(51, 51, 51); font-family: " microsoft="" yahei";"="">}</span>

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这个程序不能实现控制的。使用XF的时候要注意一下，XF是ST1的一个bit,但是在中断中,首先把ST1压入堆栈,出中断前才弹出堆栈,所以在中断中改变XF没有实际的意义。所以在C/C++加如汇编要谨慎。修改后的程序如下：

1. <span style="color: rgb(51, 51, 51); font-family: " microsoft="" yahei";"="">void main()</span>
   
2. <span style="color: rgb(51, 51, 51); font-family: " microsoft="" yahei";"="">{</span>
   
3. <span style="color: rgb(51, 51, 51); font-family: " microsoft="" yahei";"="">    init_5509();</span>
   
4. <span style="color: rgb(51, 51, 51); font-family: " microsoft="" yahei";"="">    init_timer();</span>
   
5. <span style="color: rgb(51, 51, 51); font-family: " microsoft="" yahei";"="">    while(1) </span>
   
6. <span style="color: rgb(51, 51, 51); font-family: " microsoft="" yahei";"="">    {</span>
   
7. <span style="color: rgb(51, 51, 51); font-family: " microsoft="" yahei";"="">           asm(" NOP");</span>
   
8. <span style="color: rgb(51, 51, 51); font-family: " microsoft="" yahei";"="">           if (Flag>10)</span>
   
9. 
   
10. 
    
11. <span style="color: rgb(51, 51, 51); font-family: " microsoft="" yahei";"="">              asm(" SSBX XF");</span>
    
12. 
    
13. 
    
14. <span style="color: rgb(51, 51, 51); font-family: " microsoft="" yahei";"="">          else</span>
    
15. 
    
16. 
    
17. <span style="color: rgb(51, 51, 51); font-family: " microsoft="" yahei";"="">             asm(" RSBX XF");</span>
    
18. <span style="color: rgb(51, 51, 51); font-family: " microsoft="" yahei";"="">    }</span>
    
19. <span style="color: rgb(51, 51, 51); font-family: " microsoft="" yahei";"="">}</span>
    
20. 
    
21. 
    
22. <span style="color: rgb(51, 51, 51); font-family: " microsoft="" yahei";"="">interrupt void int_timer0()</span>
    
23. <span style="color: rgb(51, 51, 51); font-family: " microsoft="" yahei";"="">{</span>
    
24. <span style="color: rgb(51, 51, 51); font-family: " microsoft="" yahei";"="">       Flag=Flag+1; </span>
    
25. <span style="color: rgb(51, 51, 51); font-family: " microsoft="" yahei";"="">       if (Flag>20)</span>
    
26. 
    
27. 
    
28. <span style="color: rgb(51, 51, 51); font-family: " microsoft="" yahei";"="">       Flag=0;</span>
    
29. <span style="color: rgb(51, 51, 51); font-family: " microsoft="" yahei";"="">}</span>

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这个程序就好使了。