DSP2000汇编语言，看别人程序遇到一个难点

只看该作者 · 2013-7-10 23:44

难点在于，我实在不明白"varStartPtr"在程序中是什么作用？以下是整个工程文件出现过“varStartPtr”的地方。

h文件中：
varStartPtr .usect "BLDC_ISRvarSec",1 ;Must at the biginning of the RAM variables
.global varStartPtr ;It is also double as ISR internal status register

//***ISR internal status
//***ADDR -- varStartPtr
#define ST_ISRLoopBit 0 //bit 0: 1, the first cycle; 0, the 2nd cycle with loop update and
//calculation. After reset, it is 0.
#define StartStepsBits 0xE //bits 1,2,3; the startup steps; max of 7 (It has to be bit 1~3)
#define ILoopENBit 4 //bit 4; 1, the current loop enabled;0,disabled

asm文件中
MOVL XAR6,#varStartPtr
MOV @AR7,#(varEndPrt-varStartPtr);
MOVW DP,#varStartPtr                            ;set DP
TBIT @varStartPtr, #ST_ISRLoopBit                            ;ST_ISRLoopBit=0
AND @varStartPtr, #((~(StartStepsBits))&(~(1<<ILoopENBit)))
TSET @varStartPtr, #ILoopENBit                            ;enable the loop
ADD    @varStartPtr,#2                                     ;point to next step