Setup is using an NI9263 Analog Output card in a cDaq9178 chassis.
I am trying to output 4 channels of analog output data each at 100kS/sec to this card using the python nidaqmx library. Sample code:
self.output_channels = np.zeros(
(len(self.device.ao_physical_chans), self.SAMPLE_COUNT),
np.float64,
)
self.task_name = f"{self.device_name}_analog_output_task"
self.create_task(self.task_name)
# Add analog output channels to the task for each channel
for channel in self.device.ao_physical_chans:
self.task.ao_channels.add_ao_voltage_chan(
channel.name, min_val=self.MINIMUM_VOLTAGE, max_val=self.MAXIMUM_VOLTAGE
)
self.task.timing.cfg_samp_clk_timing(self.SAMPLING_RATE, sample_mode=AcquisitionType.CONTINUOUS, samps_per_chan=self.SAMPLE_COUNT)
self.task.channels.ao_data_xfer_req_cond = OutputDataTransferCondition.ON_BOARD_MEMORY_LESS_THAN_FULL
self.task.channels.ao_data_xfer_mech = DataTransferActiveTransferMode.DMA
self.task.simultaneous_ao_enable = True
self.task.out_stream.regen_mode = RegenerationMode.DONT_ALLOW_REGENERATION
# Initialize StreamWriter
self.stream_writer = AnalogMultiChannelWriter(self.task.out_stream, auto_start=False)
# Initial write, defines the buffer size - this must be done before registering the callback
self.chunk_size = 1000
self.num_chunks = int(self.SAMPLE_COUNT / self.chunk_size) # this must be a whole number
self.current_chunk = 0
a = self.output_channels[:,self.current_chunk*self.chunk_size:(self.current_chunk+1)*self.chunk_size]
self.stream_writer.write_many_sample(np.array(a))
def write_callback(task_handle, every_n_samples_event_type,
number_of_samples, callback_data):
a = self.output_channels[:,self.current_chunk*self.chunk_size:(self.current_chunk+1)*self.chunk_size]
self.stream_writer.write_many_sample(np.array(a))
self.current_chunk += 1
if self.current_chunk >= self.num_chunks:
self.current_chunk = 0
return 0 # callback must return an integer, otherwise callback throws a bunch of errors
self.task.register_every_n_samples_transferred_from_buffer_event(self.chunk_size, write_callback)
self.task.start()
This works well except for intermittent errors as follows:
nidaqmx.errors.DaqWriteError: DAC conversion attempted before data to be converted was available.
Decrease the output frequency to increase the period between DAC conversions, or reduce the size of your output buffer in order to write data more often. If you are using an external clock, check your signal for the presence of noise or glitches.
Task Name: cDAQ1Mod4_analog_output_task
Status Code: -200018
This error happens after anywhere from 10 seconds to 15 minutes. Is there a setting or configuration that I can use to stop this from happening. The system seems sufficiently fast to stream this amount of data, the CPU running this is only at 33% utilisation.
I tried setting the underflow behaviour but that doesn't seem to be supported by this equipment.
I have tried to set variously smaller buffer sizes as per the error message (see the chunking of data above) but haven't seen any improvement. It would also be great if the error message told me how many samples were ready instead of just not enough. This is difficult to find in the nidaqmx library.
I am also running this in an independent python process to limit interference with the callback but I'm unsure if the issue is there or in the NI library itself. I have put in various timing checks sometimes there is a longer delay than usual on the callback but oftentimes there isn't.
