Digital In Sample Frequency Is Slow

[Empower]

Hi, using the GUI I'm able to sample at 100 MHz.  I'd like to replicate this is software using pydwf or the SDK.

Here is my example using pydwf.  I have two questions when running this code.

1. This is sampling at 2 MHz, but I expect 50 MHz or 100 MHz.  How to I sample at 100 MHz?  I'm not setting the divider, so I thought this would sample as fast as possible.

2. This is driving out at 1 MHz (measured externally).  I expect this should be 25 MHz.  How is the 1 MHz determined?

# %% Digilent Waveform Digital In

import pydwf
from time import sleep
import matplotlib.pyplot as plt
from pydwf import DwfState, DwfTriggerSource
from pydwf.utilities import openDwfDevice

CH = {'out': 0, 'in': 0}

def main():

    device = openDwfDevice(pydwf.DwfLibrary())
    device.paramSet(pydwf.DwfDeviceParameter.Frequency, int(100e6))

    digital_out = device.digitalOut
    digital_in = device.digitalIn

    # Configure for 1 MHz out
    digital_out.enableSet(CH['out'], True)
    digital_out.dividerSet(CH['out'], 1)
    digital_out.counterSet(CH['out'], low_count=2, high_count=2)

    digital_in.inputOrderSet(dio_first=True)

    clock_frequency = digital_in.internalClockInfo()
    divider_count = digital_in.dividerGet()
    digital_in.sampleFormatSet(num_bits=1) # 1 bit per sample format
    number_samples = 64
    digital_in.bufferSizeSet(number_samples)
    digital_in.triggerSourceSet(DwfTriggerSource.DetectorDigitalIn)
    digital_in.triggerPositionSet(0)
    digital_in.triggerSet(level_low=0, level_high=0, edge_rise=1<<CH['in'],
                        edge_fall=0)
    print(f'clock frequency: {clock_frequency/1e6} MHz')
    print(f'sample frequency: {clock_frequency/divider_count/1e6} MHz')

    digital_in.configure(reconfigure=False, start=True)

    digital_out.configure(start=True)

    while True:
        status = digital_in.status(read_data_flag=True)
        print(f'status: {status}')
        if status == DwfState.Done:
            print("done")
            break
        sleep(0.1)

    data = digital_in.statusData(number_samples)
    device.close()

    plt.plot(data, marker='.')
    plt.show()

# %% Main
if __name__ == '__main__':
    main()

 

[attila]

Hi @Empower

The digital-in sampling rate is determined by internal-clock/divider, so for 100MHz set the divider to internal-clock/100MHz

[Empower]

I added this line to the setup.  The sample rate is still slow (2 MHz).  Is this expected?

digital_in.dividerSet(int(clock_frequency/100e6))

Another odd behavior, if I change the internal clock, the first run of the script shows the correctly-changed internal clock value and the second run of the same, unmodified script shows the internal clock is 1/2 of what it is set to.  

Here I set the internal from 80 MHz to 100 MHz and the script correctly reports 100 MHz.  The script output is shown below.

Then, on my second run of the same script, the device unexpectedly reports 50 MHz.  The output of second run of the same script is shown below.

[Empower]

After double checking my digital_out on a scope, I see it is running at 25 MHz, not 2 MHz.  So my 4 samples per period is sampling at 100 MHz.  This issue is closed due to my error.  Thanks for the help.