I have an application that I need to run at a 10mSec rate (100hz) on a Windows 7/32 bit computer (that will also be running other applications at the same time). I know that windows is not an RTOS, but we are sort of stuck with a requirement to use it. This interrupt can have some minimally late (100uSec) responses, but must not drift over a prolonged time. I have a program where I have loaded and used the NtSetTimerResolution to set the timers to 10msec resolution, and then created a timer using the CreateTimerQueue/CreateTimereQueueTimer functions with a callback routine that toggles a GPIO pin (for the time being) - this produces the expected square wave, so long as I am not doing anything else with the system. When I start a couple of other processes, the accuracy of my square wave goes out the window. Is there any way to get a higher priority level on the timer interrupt (or is there another timer that I can use) that will produce a more stable output (perhaps the SMI)? My code is below, and is built using the x86 checked build environment of the Windows DDK, and run from a command shell with administrator rights:
#include <windows.h>
#include <winioctl.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <conio.h>
#include <strsafe.h>
#include <stdlib.h>
#include <stdio.h>
#include <winsock2.h>
#include <mswsock.h>
#pragma warning(disable:4127) // condition expression is constant
FARPROC pNtQueryTimerResolution;
FARPROC pNtSetTimerResolution;
static HANDLE NTDLLModuleHandle;
static HINSTANCE hInpOutDll;
typedef void ( __stdcall *lpOut32 )( short , short );
typedef short ( __stdcall *lpInp32 )( short );
typedef BOOL ( __stdcall *lpIsInpOutDriverOpen )( void );
lpOut32 gfpOut32;
lpInp32 gfpInp32;
lpIsInpOutDriverOpen gfpIsInpOutDriverOpen;
void CALLBACK TimerProc(void* lpParameter,
BOOLEAN TimerOrWaitFired);
VOID __cdecl main( void )
{
ULONG ulMinRes = 0;
ULONG ulMaxRes = 0;
ULONG ulCurRes = 0;
HANDLE phNewQueue;
HANDLE phNewTimer;
phNewQueue = CreateTimerQueue( );
NTDLLModuleHandle = LoadLibrary( "NTDLL.DLL" );
if( NULL == NTDLLModuleHandle )
{
return;
}
pNtQueryTimerResolution = GetProcAddress( NTDLLModuleHandle, "NtQueryTimerResolution" );
pNtSetTimerResolution = GetProcAddress( NTDLLModuleHandle, "NtSetTimerResolution" );
if( ( pNtQueryTimerResolution == NULL ) || ( pNtSetTimerResolution == NULL ) )
{
printf( "unable to link to ddl\n\n\n\n\n\n" );
return;
}
pNtQueryTimerResolution( &ulMinRes, &ulMaxRes, &ulCurRes );
printf( "MMR: %d %d %d\n", ulMinRes, ulMaxRes, ulCurRes );
ulMaxRes = 100000;
pNtSetTimerResolution( ulMaxRes, TRUE, &ulCurRes );
pNtQueryTimerResolution( &ulMinRes, &ulMaxRes, &ulCurRes );
printf( "MMR: %d %d %d\n", ulMinRes, ulMaxRes, ulCurRes );
hInpOutDll = LoadLibrary( "InpOut32.DLL" );
if( hInpOutDll != NULL )
{
gfpOut32 = ( lpOut32 )GetProcAddress( hInpOutDll, "Out32" );
gfpInp32 = ( lpInp32 )GetProcAddress( hInpOutDll, "Inp32" );
gfpIsInpOutDriverOpen
= ( lpIsInpOutDriverOpen )GetProcAddress( hInpOutDll, "IsInpOutDriverOpen" );
if( gfpIsInpOutDriverOpen( ) )
{
gfpOut32( 0xA01, 0x00 );
}
else
{
printf( "unable to create timer system\n\n\n\n\n\n" );
return;
}
}
CreateTimerQueueTimer( &phNewTimer, phNewQueue, TimerProc, NULL, 0, 10,
WT_EXECUTEINTIMERTHREAD );
do
{
Sleep( 1 );
} while( TRUE );
}
void CALLBACK TimerProc(void* lpParameter,
BOOLEAN TimerOrWaitFired)
{
WORD wData;
UNREFERENCED_PARAMETER ( lpParameter );
UNREFERENCED_PARAMETER ( TimerOrWaitFired );
wData = gfpInp32( 0xA00 );
wData++;
gfpOut32( 0xA00, wData );
}