ICCAVR：delay函数的汇编代码很奇怪

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nicker88|

楼主 | 2010-12-27 18:12 | 只看该作者回帖奖励

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函数, ICCAVR, 汇编代码, ST, Indirect

:       void delay(unsigned int t)
+00000095: 934A       ST    -Y,R20          Store indirect and predecrement
+00000096: 935A       ST    -Y,R21          Store indirect and predecrement
9:       for(i=0;i<t;i++)NOP();
+00000097: 2744       CLR    R20             Clear Register
+00000098: 2755       CLR    R21             Clear Register
+00000099: C003       RJMP PC+0x0004       Relative jump
9:       for(i=0;i<t;i++)NOP();
+0000009A: 0000       NOP                   No operation
9:       for(i=0;i<t;i++)NOP();
+0000009B: 5F4F       SUBI R20,0xFF       Subtract immediate
+0000009C: 4F5F       SBCI R21,0xFF       Subtract immediate with carry
9:       for(i=0;i<t;i++)NOP();
+0000009D: 1740       CP    R20,R16       Compare
+0000009E: 0751       CPC    R21,R17       Compare with carry
+0000009F: F3D0       BRCS PC-0x05       Branch if carry set
+000000A0: 9159       LD    R21,Y+          Load indirect and postincrement

为什么有那么多个for(i=0;i<t;i++)NOP();啊，
ICC里是这样
void delay(unsigned int t)
{
unsigned int i;
for(i=0;i<t;i++)NOP();
}

这个delay函数非常奇怪，进到for里面就出不来了，所以我才看他的汇编代码的，一看，为什么会有那么多个for啊，求指点

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