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TMX320C6678LE上clock函数



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以下是clock的代码

#include <stdio.h>
#include <time.h>

void main(void)
{
    int i;
    clock_t start, end, sum = 0;
    printf("Clock test start!\n");
    start = clock();
    for(i=0;i<100000000;i++)
    {
        ;
    }
    end = clock();
    sum += end - start;
    printf("Total time :  %.9f  secs .\n",(float)sum/CLOCKS_PER_SEC);
}

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运行结果

[C66xx_0] Clock test start!
[C66xx_0] Total time :  4.500000477  secs .

用秒表计时,约为9秒左右。

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time.h里的定义 :

#define CLOCKS_PER_SEC 200000000 /* 200 MHz */

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问题:

1、请问clock()是通过什么机制来计时的?

2、我上面的程序是否正确,为什么运行结果与实际相差4秒左右呢?