Fastest acquisition possible in C

DavidPARIS · ‎10-17-2012

Hi,

I am using a PCIe 6341 board and coding under visual c++ 2010. I need to do an analog acquisition of 10 points at 500kHz every 200µs. In order to be fast, I permit the card to overwrite the buffer and take the last 10 points written in the buffer. Unfortunately, the time to take the data is of 10ms which is too slow for me who need to read the data every 0.2ms. What do I do wrong ?

My code is :

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

#define DAQmxErrChk(functionCall) if( DAQmxFailed(error=(functionCall)) ) goto Error; else

#define nb_point 10
#define frequence 500000

int main(void)
{
   int32       error=0;
   TaskHandle taskHandle=0;
   int32       read;
   float64     data[nb_point];
   char        errBuff[2048]={'\0'};
   int64       samplesToAcquire=100000 ;
   int           cpt ;

   // essai pour mesure du temps
   int
       temps_initial,
       temps_final;
   float
       temps_cpu;

   /*********************************************/
   // DAQmx Configure Code
   /*********************************************/

   DAQmxErrChk (DAQmxCreateTask("",&taskHandle));
   DAQmxErrChk (DAQmxCreateAIVoltageChan(taskHandle,"Dev1/ai0","",DAQmx_Val_Cfg_Default,-10.0,10.0,DAQmx_Val_Volts,NULL));
   DAQmxErrChk (DAQmxCfgSampClkTiming(taskHandle,"",frequence,DAQmx_Val_Rising,DAQmx_Val_ContSamps,samplesToAcquire));
   DAQmxErrChk (DAQmxSetReadRelativeTo(taskHandle,DAQmx_Val_MostRecentSamp));
   DAQmxErrChk (DAQmxSetReadOffset(taskHandle,nb_point));

   /***********************/
   // debut de mesure avant le lancement de la tache
   /***********************/
   printf("Parti?\n");
   getchar();

   /*********************************************/
   // DAQmx Start Code
   /*********************************************/
   DAQmxErrChk (DAQmxStartTask(taskHandle));

   /*********************************************/
   // DAQmx Read Code
   /*********************************************/
   for ( cpt = 0 ; cpt <11 ; cpt++ )
   {
       temps_initial = clock ();
       DAQmxErrChk (DAQmxReadAnalogF64(taskHandle,nb_point,10.0,DAQmx_Val_GroupByChannel,data,nb_point,&read,NULL));
       /***********************/
       // fin de mesure du temps
       /***********************/
       temps_final = clock ();
       temps_cpu = ((float)temps_final - temps_initial)/CLOCKS_PER_SEC;
       printf("Temps d execution : %f\n",temps_cpu);
       printf("Acquired %d points\n",read);
   }

Error:
   if( DAQmxFailed(error) )
       DAQmxGetExtendedErrorInfo(errBuff,2048);
   if( taskHandle!=0 ) {
       /*********************************************/
       // DAQmx Stop Code
       /*********************************************/
       DAQmxStopTask(taskHandle);
       DAQmxClearTask(taskHandle);
   }
   if( DAQmxFailed(error) )
       printf("DAQmx Error: %s\n",errBuff);
   printf("End of program, press Enter key to quit\n");
   getchar();
   return 0;
}