Thank you Pierre D. for your answer.
Sorry for the delay.
It is what I have tried (Here is a piece of truncated code where i have kept the interesting part)
1 - Creation of the counter and the data task using or counter as clock source
Only the counter task is started, the DO task (patternHandle) is not yet started
Note : The patternHandle Task is configured to write on 2 DO with different pattern and potentially simultaneously.
For my case e.g :
at t = 1 ms, I want to generate pattern_a_1 on the first DO during 10 ms
at t = 5 ms, generate another pattern_b on the second DO during 20 ms .
at t = 12 ms, generate another pattern_a_2 on the first DO during 15 ms
and so on.
That's why once this task is started, it will never be stopped until the program is finished.
/* Create counter task */
error = DAQmxCreateTask(taskName, &result->counter);
/* Create the channel to generate the pulses */
error = DAQmxCreateCOPulseChanFreq(result->counter,
result->counterName,
COPulse_nameToAssignChannel,
DAQmx_Val_Hz,
DAQmx_Val_Low,
COPulse_initialDelay,
COPulse_frequency,
COPulse_dutyCycle);
/* Configure samples for our counter task */
DAQmxCfgImplicitTiming(result->counter, DAQmx_Val_ContSamps, (uint) COPulse_frequency);
/* Create the task which will generate data using the counter as clock source */
error = DAQmxCreateDOChan(result->patternHandle,
DOChan_physicalChannel,
DOChan_virtualChannelName,
DAQmx_Val_ChanForAllLines);
error = DAQmxCfgSampClkTiming(result->patternHandle,
clockSource, /* ctr1 timer is associated to PFI13 source */
COPulse_frequency,
DAQmx_Val_Rising,
DAQmx_Val_ContSamps,
512);
/* Start our counter task */
error = DAQmxStartTask(result->counter);
2 - Creation of the signal task (not started for the moment)
/* Create or Signal task */
error = DAQmxCreateTask(taskName,
&result->SignalTask);
/* Add DO to the task */
error = DAQmxCreateDOChan(result->SignalTask,
DOChan_PhysicalChannel,
DOChan_VirtualChannel,
DAQmx_Val_ChanForAllLines);
3 - When I receive a " start top" I would generate the data on a given DO and the sig and start them at the same time
For that, when I receive the top this is what i do sequentially :
- Write the sample
- Start the signal task
/* Write our samples to the data task and start the task if it is not started */
error = DAQmxWriteDigitalU32(fsk->patternHandle,
SAMPLE_COUNT,
1,
-1,
DAQmx_Val_GroupByChannel,
fskSamples,
&returnValue,
NULL);
/* Set the output of our sigTask to 1 */
error = DAQmxWriteDigitalU32(sigTask,
1,
1,
-1,
DAQmx_Val_GroupByChannel,
&value,
NULL,
NULL);
4- When I receive the "stop top" I don't stop both the data and signal task but write 0 as pattern for data task and 0 as output for signal task
/* Write our samples = table of sample count set 0 to the data task */
error = DAQmxWriteDigitalU32(fsk->patternHandle,
SAMPLE_COUNT,
1,
-1,
DAQmx_Val_GroupByChannel,
fskSamples, /* all the sample count to 0 */
&returnValue,
NULL);
/* Set the output of our sigTask to 1 */
error = DAQmxWriteDigitalU32(sigTask,
1,
1,
-1,
DAQmx_Val_GroupByChannel,
&value, /* Value = 0 for the concerned DO */
NULL,
NULL);
What I observe is a delay between the start or the stop of data task and sig task and it always arrives :
=> when i receive the "start top" : the output data pattern start emitting after the signal while the data task was written before the sig task one (attachment : data_start_after_sig, data in pink, sig in yellow)
=> when i receive the "stop top" : the output data pattern stop emitting after the signal while the data task was written to 0 before the sig task one (attachment : data stop_after_sig, data in pink, sig in blue)
Trying to start the data and sig starting and stopping at the same time, I have tried different solution (I exclude the trigger my PXI 6259 card does not support software and digital trigger)
Here are explained my variant :
Step 1 : the counter task is not started, only the pattern task is started (and emit nothing because of the counter task which is not started)
Step 3 : when receiving the "start top", just a little time before emitting data (at t0 - delta), i write my pattern to the data task (digitalWrite) and configure a delay before starting the counter task with DAQmxSetCOPulseFreqInitialDelay with a delay of delta.
When the time is up to start generating, i write 1 to the output of the sig task (other variant i stop the sig task)
Step 4 : I stop the data task and the sig task when the time is up to stop emitting
I have never succeeded to have a data and sig task starting and stopping at the same time.
Is this delay usual ?
I have a look to the code in attachement and i'll let you know.
Thank you very much for your help
Jank
