Python nidaqmx stream read does not change on every read

Question

What I'm trying to do is setup 16 analog input channels, sample them constantly at a given rate and read 1 sample from each channel when calling the read function. Ideally I would like to read the newest sample so I can timestamp it when reading.

The problem is that the readings do not change from read to read, only after a few seconds. If I adjust the sampling speed, I can get to a situation where I get an error saying the software can't keep up with the hardware sampling rate.

Which part of my code is wrong?

import numpy
import nidaqmx
from nidaqmx.stream_readers import AnalogSingleChannelReader, AnalogMultiChannelReader
from nidaqmx.constants import Edge, AcquisitionType

# Create a task and a reader
task = nidaqmx.Task()

values_read = numpy.zeros(16, dtype = numpy.float64)

task.ai_channels.add_ai_current_chan('cDAQ1Mod2/ai0:15')
task.timing.cfg_samp_clk_timing(rate = 1000, active_edge = Edge.RISING, sample_mode = AcquisitionType.CONTINUOUS, samps_per_chan = 1)
reader = AnalogMultiChannelReader(task.in_stream)

task.start()
while 1:
    reader.read_one_sample(values_read)
    print(values_read)

Answer 1

The sampling rate is 1000 but you are reading only one sample each time. Usually, each Read call takes a few milliseconds. You are not reading fast enough hence the buffer overflow error. Suggestions:

1. Reduce sample rate.
2. Read more samples per Read call.
3. Since you want to read only the latest data and timestamp yourself, you can use the On Demand software timed acquisition. See example ai_voltage_sw_timed.py