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emmai

using winio.dll to read 8253 timer

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I'd like to get accurate timer by using read 8253 directly,I'm now using winio.dll to do this,the code is like this: if (InitializeWinIo()) { // Under Windows NT/2000/XP, after calling InitializeWinIo, // you can call _inp/_outp instead of using GetPortVal/SetPortVal DWORD dwCount = 0; DWORD dwBegin = GetTick(); LARGE_INTEGER liQ,liC1,liC2; DWORD dw1 = GetTickCount(); QueryPerformanceFrequency(&liQ); QueryPerformanceCounter(&liC1); DWORD dwOldProcessP = GetPriorityClass(GetCurrentProcess()); DWORD dwOldThreadP = GetThreadPriority(GetCurrentThread()); SetPriorityClass(GetCurrentProcess(), REALTIME_PRIORITY_CLASS); SetThreadPriority(GetCurrentThread(), THREAD_PRIORITY_TIME_CRITICAL); do { //printf("%d\n",dwBegin); DWORD dwTick = GetTick(); dwCount += dwBegin > dwTick ? dwBegin - dwTick : 65535 + dwBegin - dwTick; dwBegin = dwTick; QueryPerformanceCounter(&liC2); }while((liC2.QuadPart - liC1.QuadPart) / (double)liQ.QuadPart < 1.000000); SetThreadPriority(GetCurrentThread(), dwOldThreadP); SetPriorityClass(GetCurrentProcess(), dwOldProcessP); printf("QueryPerformanceCounter : %f\n",(liC2.QuadPart - liC1.QuadPart) / (double)liQ.QuadPart); printf("8253 Tick : %d\n",dwCount); DWORD dw2 = GetTickCount(); printf("GetTickCount : %d\n",dw2 - dw1); ShutdownWinIo(); } this is a test program,I loop one second,and count the 8253 ticks,that result should be ~1193177. it works on many machines,but on my machine,the result is ~2386362,twice the right value! can anyone help me?

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Be aware that depending on what mode they're set up in, some timers count by twos instead of ones. Check the count mode selection?

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