def AI_filter_delay(device_name):
"""Determine the filter delay for dynamic signal acquistion devices.
Returns the delay in clock cycles. Absolute delay will vary with sample rate.
Args:
device_name (str): NI-MAX device name
Returns:
int: Number of analog input delays ticks between task start and acquisition start.
"""
if 'PFI0' not in DAQmxGetDevTerminals(device_name):
return None
task = Task()
clock_terminal = '/' + device_name + '/PFI0'
rate = DAQmxGetDevAIMaxSingleChanRate(device_name)
Vmin, Vmax = DAQmxGetDevAIVoltageRngs(device_name)[0:2]
num_samples = 1000
chan = device_name + '/ai0'
task.CreateAIVoltageChan(
chan, "", c.DAQmx_Val_PseudoDiff, Vmin, Vmax, c.DAQmx_Val_Volts, None
)
task.CfgSampClkTiming(
"", rate, c.DAQmx_Val_Rising, c.DAQmx_Val_ContSamps, num_samples
)
task.CfgDigEdgeStartTrig(clock_terminal, c.DAQmx_Val_Rising)
start_filter_delay = float64()
sample_timebase_rate = float64()
# get delay in number of clock samples
task.SetAIFilterDelayUnits("", c.DAQmx_Val_SampleClkPeriods)
task.GetAIFilterDelay("", start_filter_delay)
task.GetSampClkTimebaseRate(sample_timebase_rate)
task.ClearTask()
return int(start_filter_delay.value)
