Create a synchronization example for TDMS logging

[HugoRamsey]

The examples in synchronisation (required for multiple task types eg. analogue in and counter in) do not show how to log all tasks to a single TDMS file. It would be useful to have all synchronised tasks in one place as the NI hardware supports multiple tasks.

Doing something like this raises the error "File specified is already opened for output. NI-DAQmx requires exclusive write access.

ai_task.in_stream.configure_logging( filepath, LoggingMode.LOG, operation=LoggingOperation.CREATE_OR_REPLACE ) ci1_task.in_stream.configure_logging( filepath, LoggingMode.LOG, operation=LoggingOperation.OPEN )

AB#3252273

[zhindes]

Hmm, I don't think this is possible with our TDMS APIs. But I'm not 100% sure. I'll ponder.

[HugoRamsey]

Ah... Thanks for having a ponder. Would it then be best to log to a different TDMS for each task and post-process into one? Had a go but not sure how stable this is, could the callback cause a delay that means the buffer overflows...

with nidaqmx.Task() as ai_task, nidaqmx.Task() as ci1_task, nidaqmx.Task() as ci2_task, nidaqmx.Task() as clk_task:

    def callback(task_handle, every_n_samples_event_type, number_of_samples, callback_data):
        """Callback function for reading signals."""
        nonlocal total_ai_read
        nonlocal total_ci1_read
        nonlocal total_ci2_read
        ai_read = ai_task.read(number_of_samples_per_channel=number_of_samples)
        ci1_read = ci1_task.read(number_of_samples_per_channel=number_of_samples)
        ci2_read = ci1_task.read(number_of_samples_per_channel=number_of_samples)
        total_ai_read += len(ai_read)
        total_ci1_read += len(ci1_read)
        total_ci2_read += len(ci2_read)
        print(f"\t{len(ai_read)}\t{len(ci1_read)}\t{len(ci2_read)}\t\t{total_ai_read}\t{total_ci1_read}\t{total_ci2_read}", end="\r")

        return 0
    

    #Configure sample clock
    clk_task.co_channels.add_co_pulse_chan_freq(
        counter="Dev1/ctr3",
        freq=sample_rate,
    )
    clk_task.timing.cfg_implicit_timing(sample_mode=AcquisitionType.CONTINUOUS)


    #Configure ai channels
    ai_task.ai_channels.add_ai_voltage_chan("Dev1/ai0", "Torque01")
    ai_task.ai_channels.add_ai_voltage_chan("Dev1/ai1", "Torque02")
    ai_task.timing.cfg_samp_clk_timing(sample_rate, "/Dev1/Ctr3InternalOutput", sample_mode=AcquisitionType.CONTINUOUS)
    ai_task.register_every_n_samples_acquired_into_buffer_event(sample_rate, callback)


    # Configure ci channels
    #ci 1
    ci1_chan = ci1_task.ci_channels.add_ci_count_edges_chan(
        "Dev1/ctr0",
        "Rotations01",
        edge=Edge.RISING,
        initial_count=0
    )
    ci1_chan.ci_count_edges_term = "/Dev1/PFI0"
    ci1_task.timing.cfg_samp_clk_timing(
        sample_rate, "/Dev1/Ctr3InternalOutput", sample_mode=AcquisitionType.CONTINUOUS
    )
    #ci 2
    ci2_chan = ci2_task.ci_channels.add_ci_count_edges_chan(
        "Dev1/ctr1",
        "Rotations02",
        edge=Edge.RISING,
        initial_count=0
    )
    ci2_chan.ci_count_edges_term = "/Dev1/PFI1"
    ci2_task.timing.cfg_samp_clk_timing(
        sample_rate, "/Dev1/Ctr3InternalOutput", sample_mode=AcquisitionType.CONTINUOUS
    )

    
    #configure logging
    ai_task.in_stream.configure_logging(
        "{0}_ai.tdms".format(filepath), 
        LoggingMode.LOG_AND_READ,
        operation=LoggingOperation.CREATE_OR_REPLACE
    )
    ci1_task.in_stream.configure_logging(
        "{0}_ci1.tdms".format(filepath), 
        LoggingMode.LOG_AND_READ,
        operation=LoggingOperation.CREATE_OR_REPLACE
    )
    ci2_task.in_stream.configure_logging(
        "{0}_ci2.tdms".format(filepath), 
        LoggingMode.LOG_AND_READ,
        operation=LoggingOperation.CREATE_OR_REPLACE
    )
    
    clk_task.start()
    ci1_task.start()
    ci2_task.start()
    ai_task.start()

    print("Acquiring samples continuously. Press Enter to stop.\n")
    print("Read:\tAI\tCI1\tCI2\tTotal:\tAI\tCI1\tCI2")
    input()

    ai_task.stop()
    ci1_task.stop()
    ci2_task.stop()
    clk_task.stop()

    print(f"\nAcquired {total_ai_read} total AI samples and {total_ci1_read} total CI1 samples.")

[zhindes]

That approach looks sound. Your example isn't combining, but you'll end up with 3 TDMS files that you could merge as a post-process. Some thoughts:

• You're synchronizing by using a shared CO task - good!
• Yes, if your callbacks are slow you could get behind in your buffer and eventually overflow. But you're not doing any significant processing, so I think you'll be OK. Especially true since you're only getting a callback once per second. I recommend 10x per second or slower.