Greeting fellow data acquirerers,
I have a question regarding the NI DAQmx C API. I have a very basic application in Qt (for GUI) to start, stop, reconfigure and plot a measurement with a USB-6255 DAQ. The program is built up as follows:
- At the start of the program I create a task
- The task is configured with some initial parameters
- Upon button press this task can be started and stopped
- There are button for changing the sample rate, samples per channel and dynamic range
- Upon changing a value in any of the aforementioned controls the task is stopped, the parameters reconfigured and started again
The initial initialization consists of:
- DAQmxCreateAIVoltageChan to add the required channels to the task
- DAQmxCfgSampClkTiming to configure the sample clock
- DAQmxSetBufInputBufSize to 10 times the samples per channel value
- DAQmxRegisterEveryNSamplesEvent to configure the callback
The problem seems to be, when I choose certain parameters (for example 10000 Hz rate and 10000 samples per channel) DAQmx issues an error that my application can't keep up with the acquisition. I reconfigure the task in the following way:
- If the task was running, stop it
- Call DAQmxCfgSamlClkTiming with the new parameters
- Call DAQmxSetAIMax/Min with the new parameters
- Call DAQmxSetBufInputBufSize to set the buffer to 10 times the new samples per channel value
- Unregister my EveryNSamplesEvent
- Register an EveryNSamplesEvent with the new parameters
- Restart the task, if it was running before
Now comes the twist. If, instead of stopping, reconfiguring and restarting the task, I clear the task and just perform the initial configuration with the new parameters everything works well. So my question in short would be: What happens between deleting, recreating and configuring the task that calling the configuration functions repeatedly does not do? In my opinion I am performing the same configuration steps (obviously without the channel creation) in the initialization and in the reconfiguration, so it seems odd to me that I get different results.
I would be happy about any suggestions. Thanks in advance,
FB.
