I'm a research assistant for Northeastern University in Boston. We
had a class using the 6024E PCI card in our Electrical Engineering lab and are
now trying to migrate to a USB 6009 in order to move into a standard computer
lab and expand the number of sections being taught.
This lab is taught to first-year engineering undergraduates of all
disciplines, some of whom have no programming background. As well-written
as NIDAQmx.h is, we believe it may be intimidating for our purposes. Therefore,
I'm attempting to develop a "front-end" so that they only have to
code, say, write_digital(14) to put [0111] on P0.0-P0.3 (with a #include
statement at the top, of course). However, I've run into a problem.
I'm using Visual C++ 2008 without Measurement Studio. I've stored
the task inside a class, as that's the best method I can think of to let the
students write their own .cpp file (and #include my class as a .h file).
I am able to run the attached code once (to write 13, in this example) but the
task is somehow rendered invalid between writing 13 and attempting to write
14. The 14 is not written, and I get an error (reprodeuced below). I've tried using DAQmxIsTaskDone() to look into where it may be turning invalid, but that only
confused me further (saying it's still running even after throwing the error, giving me different results depending on where I put the
function call with no other changes, etc.).
I'm thinking it is related to a task's behaviour at the end of a block,
but I'm not sure. I'm completely open to any advice or suggestions anyone
may have, including a full re-design if that's the best option.
Thanks in advance!
-Geoff
This is the output:
107
108
DAQmx Error: Measurements: Task specified is invalid or does not exist.
Status Code: -200088
of this code:
#define DAQmxErrChk(functionCall) if( DAQmxFailed(error=(functionCall)) ) goto Error; else
class TaskEnvelope{
TaskHandle task;
public:
TaskEnvelope(){
task = 0;
DAQmxCreateTask("",&task);
DAQmxCreateDOChan(task,"Dev1/port0/line0:7","",DAQmx_Val_ChanForAllLines);
}
void write(int data){
int temp = data%256;
uInt8 output[8];
int32 error=0;
char errBuff[2048]={'\0'};
for(int i = 0; i < 8; i++){
output[i] = temp % 2;
temp = temp / 2;
}
DAQmxStartTask(task);
DAQmxErrChk (DAQmxWriteDigitalLines(task,1,1,10.0,DAQmx_Val_GroupByChannel,output,NULL,NULL));
Error:
if( DAQmxFailed(error) )
DAQmxGetExtendedErrorInfo(errBuff,2048);
if( task!=0 ) {
DAQmxStopTask(task);
DAQmxClearTask(task);
}
if( DAQmxFailed(error) )
printf("DAQmx Error: %s\n",errBuff);
}
};
int main(void){
TaskEnvelope env;
for(int i = 13; i < 15; i++){
cout<<i<<endl;
env.write(i);
}
return 0;
}
