Delta time comparison of Socketcan gs_usb hardware and software timestamps

timestamping-comparison.py

import datetime
import statistics
import plotly.express as px
import pandas as pd
from cantools.logreader import Parser

# path to comparison files
software_file = "/Users/john/Desktop/software-timestamps.log"
hardware_file = "/Users/john/Desktop/hardware-timestamps.log"

def calc(file: str):
    deltas = []
    micros_delta = []


    with open(file) as fd:
        log = Parser(fd).iterlines()
        last = next(log)[1]

        for _, frame in log:
            if last and frame:
                deltas.append(frame.timestamp - last.timestamp)
                last = frame

    micros = [x.microseconds for x in deltas]
    micros_delta = [abs(2000 - x) for x in micros]

    max_percent = (max(micros_delta) / 2000) * 100

    print(f"Max: {max(micros)} µs")
    print(f"Min: {min(micros)} µs")
    print("Stddev: {:.1f} µs".format(statistics.stdev(micros)))
    print("Variance: {:.1f} µs".format(statistics.variance(micros)))
    print(f"Largest percentage slip: {max_percent}%")
    print(f"Median: {statistics.median(deltas)}")

    return pd.DataFrame({
        'deltatime': deltas,
        'micros': micros,
    })

# process

hardware = calc(hardware_file)
software = calc(software_file)

# plot

if len(hardware) > len(software):
    df = pd.DataFrame({'Hardware': hardware[0:len(software)]['micros'], 'Software': software['micros']})
else:
    df = pd.DataFrame({'Hardware': hardware['micros'], 'Software': software[0:len(hardware)]['micros']})

fig = px.scatter({'Software': df['Software'], 'Hardware': df['Hardware']}, labels={'value': 'delta µs', 'variable': 'Timestamping'}, title='Delta time comparison of Socketcan gs_usb hardware and software timestamps for 2 ms cycle CAN message')
fig.show()
fig.write_html("timestamping-scatter.html")

hist = px.histogram(df, nbins=800, labels={'value':'delta us', 'variable': 'Timestamping'}, title='Delta time comparison of Socketcan gs_usb hardware and software timestamps for 2 ms cycle CAN message')
hist.show()
hist.write_html("timestamping-hist.html")

box = px.box(df, points='all', labels={'value':'delta µs', 'variable':'Timestamping'}, title='Delta time comparison of Socketcan gs_usb hardware and software timestamps for 2 ms cycle CAN message')
box.show()
box.write_html("timestamping-box.html")

Test files from a candleLight_fw (Entree) interface candump can0 -l -H (hardware) and candump can0 -l (software) receiving messages from a STM32F4 sending every 2 ms in a SysTick ISR (ext osc) using kernel 6.1 gs_usb module:

https://www.dropbox.com/s/phoksassj8jzgx8/hardware-timestamps.log?dl=0
https://www.dropbox.com/s/bn6s6qd5bydsvuw/software-timestamps.log?dl=0