NI-6509 Python performance issue when writing to Output

[Jeff@Evident]

Hi All, I'm using an NI-6509 / PCI card   to generate encoder pulses. All we do is write to the outputs every 2ms. It seems the write is a blocking call, and when we check the min/max time for a write is varies from 0.1ms to 1ms, sometimes we even get write times up to 2ms, which causes some issues.

So I have 2 questions:

1.  Is there a way to make this call "non-blocking"

2.  Why does the call take so much time

Here is the Python code to create the task:

    def __init__(self😞

        try:  

            self.OutputStates = [False,False,False,False,False,False,False,False]  # NI DAQ port 0 initial

            # Configure and setup the tasks

            self.task0 = nidaqmx.Task()

            self.task0.do_channels.add_do_chan("Dev2/port0/line0:7" ,line_grouping=LineGrouping.CHAN_PER_LINE)

            self.task0.start()

            # set default values

            self.task0.write(self.OutputStates)

        except Exception as e:

            self.task0 = None

            print("NationalInstrumentGpio::__init__() exception: {}".format(e))

Here is the write method, called every 2msec

    def WriteOutputs(self😞

        try:  

            self.task0.write(self.OutputStates)

        except Exception as e:

            print("NationalInstrumentGpio::SetOutputState() exception: {}".format(e))

            raise NationalInstrumentGpioException("NationalInstrumentGpio::SetOutputState() exception: {}".format(e))

[santo_13]

In my opinion, you have got the wrong device for your job. 6509 is software timed digital I/O - this means the software defines the duration between any digital state change. With this said, there are software overheads (like the driver) and in the end, you're at the mercy of your OS to let you execute at the time you want it to execute (which is typical of Windows).

You need a device with Hardware timed digital output (this means a dedicated circuit on the device ensures that the digital states are updated at specified time intervals without any interruption).

[Jeff@Evident]

Thank you very much Santhosh, can you suggest some PCI cards with hw timed digital outputs ? We need about 8 IOs, 5volts.

Best regards,

Jeff

[santo_13]

Going the PCI or PCIe route will fetch far fewer options for the cards and most of them are obsolete. Before I get to suggest a new HW, please elaborate on your requirements to make the right choice.