用8254定时芯片计算cpu周期的方式取CPU频率

#include "windows.h"

//RDTSC-Read Time-Stamp Counter  

//自开机以来CPU经历的时钟周期数  

unsigned __int64 RDTSC()  

{  

    __asm _emit 0x0F;  

    __asm _emit 0x31;  

}  

   

//CPU的频率  

double CpuFrequency()  

{  

    //On a multiprocessor machine, it should not matter which processor is called.  

    //However, you can get different results on different processors due to bugs in  

    //the BIOS or the HAL. To specify processor affinity for a thread, use the SetThreadAffinityMask function.  

    HANDLE hThread=GetCurrentThread();  

    SetThreadAffinityMask(hThread,0x1);    

     

    //主板上高精度定时器的晶振频率  

    //这个定时器应该就是一片8253或者8254  

    //在intel ich7中集成了8254  

    LARGE_INTEGER lFrequency;  

    QueryPerformanceFrequency(&lFrequency);  

    //printf("高精度定时器的晶振频率：%1.0fHz.\n",(double)lFrequency.QuadPart);  

   

    //这个定时器每经过一个时钟周期，其计数器会+1  

    LARGE_INTEGER lPerformanceCount_Start;  

    QueryPerformanceCounter(&lPerformanceCount_Start);  

   

    //RDTSC指令:获取CPU经历的时钟周期数  

    __int64 _i64StartCpuCounter=RDTSC();  

   

    //延时长一点,误差会小一点  

    //int nTemp=100000;  

    //while (--nTemp);  

    Sleep(200);   

   

    LARGE_INTEGER lPerformanceCount_End;  

    QueryPerformanceCounter(&lPerformanceCount_End);  

   

    __int64 _i64EndCpuCounter=RDTSC();  

   

    //f=1/T => f=计数次数/(计数次数*T)  

    //这里的“计数次数*T”就是时间差  

    double fTime=((double)lPerformanceCount_End.QuadPart-(double)lPerformanceCount_Start.QuadPart)  

        /(double)lFrequency.QuadPart;  

   

    return (_i64EndCpuCounter-_i64StartCpuCounter)/fTime;  

}  

   

int main(int argc, char* argv[])  

{  

    printf("CPU频率为:%1.6fMHz.\n",CpuFrequency()/1000000.0);  

    return 0;  

}