How do I acquire multiple channels with NIDAQmxBase?

Question

Sorry for the double post, I just thought my previous message subject looked more like a tutorial rather than a question.
My question is the same, I am looking to acquire more than 2 channels worth of data using C++ and NIDAQmxBase. I have tried initializing with and without the timer. Without the timer I will get an actual response, with it the program stalls. I don't know if I am splitting up the data correctly...not sure how the DAQmx_Val_GroupByChannel works or whether I should use GroupByScanNumber.
Here's my code (snippets from my prog):
char Dev1_joint1_channels[] = "Dev1/ai0:1";
char Dev1_joint2_channels[] = "Dev1/ai2:3";//the only reason I split this is to test with and without
//buffersize is 500
uInt64 samplesPerChan = bufferSize/4;
// Data read parameters
float64 data[bufferSize];
int32 pointsToRead = bufferSize;
/---------Initialize the task--------------------/
DAQmxErrChk (DAQmxBaseCreateTask("",&taskHandle));
DAQmxErrChk (DAQmxBaseCreateAIVoltageChan(taskHandle,Dev1_joint1_channels,"",DAQmx_Val_Diff,min,max,DAQmx_Val_Volts,NULL));
DAQmxErrChk (DAQmxBaseCreateAIVoltageChan(taskHandle3,Dev1_joint2_channels,"",DAQmx_Val_Diff,min,max,DAQmx_Val_Volts,NULL));
DAQmxErrChk (DAQmxBaseStartTask(taskHandle));
WHILE LOOP
/---------Acquire data--------------------------/
DAQmxErrChk (DAQmxBaseReadAnalogF64(taskHandle,pointsToRead,timeout,DAQmx_Val_GroupByChannel,data,samplesPerChan,&pointsRead,NULL));
/---------Assign to variables after averaging---/
joint1_chanA = arrayAverage(data,0,pointsToRead/4);
joint1_chanB = arrayAverage(data,pointsToRead/4,pointsToRead/4);
joint2_chanA = arrayAverage(data,pointsToRead/2,pointsToRead/4);
joint2_chanB = arrayAverage(data,pointsToRead*3/4,pointsToRead/4);
}//END WHILE LOOP
This works perfectly for just 2 channels, without even using the timer. I tried to stick the timer in, but the acquisition would not even go at that point. With 2 channels, I simply average the first half of data and assign it to the appropriate variable and then do the same for the second half. This works very well for just 2 channels, it's when i get into 4 channels that the data is messy.
Help is appreciated!
Thank you!
Nathan
[email protected]

Answer 1

>I tried to stick the timer in, but the acquisition would not even go at that point.
What timer? There's no timer in your code. Since putting in the timer makes it stop, that would seem to be the problem, and you're going to have to show it to us.
A quick and not-very-careful read of your code seems to be OK, assuming the variables whose definitions and initialization you have left out are OK.
>not sure how the DAQmx_Val_GroupByChannel works or whether I should use GroupByScanNumber
The way you're doing the averaging requires DAQmx_Val_GroupByChannel.
John Weeks
WaveMetrics, Inc.
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www.wavemetrics.com