standarddeviant

Hardware Clock Drift Measurement with Python + NTP

I've been tinkering with microcontroller code and have learned about "real time clocks" and how computers attempt to keep accurate time.

More recently, I've become loosely familiar with NTP at the UDP level and realized that I could measure the clock drift over time just by repeatedly fetching hardware time and NTP time and comparing their differences over time.

I found that my desktop machine's RTC drifted by about 6 seconds in 33 hours. This kind of error is acceptable for some applications and unacceptable for others.

I did this on a Windows 10 machine, but I first

	import threading
	import serial
	import queue
	import time

	# make thread-safe queue for data logging/writing
	global_dataMsgQ = queue.Queue()

	# make a thread-safe queue to inform different threads when it's time to stop
	global_stopQ = queue.Queue()


	#include <stdio.h> // for printf
	#include <math.h> // for testing only, not used by cordic
	#include "cordic-32bit.h" // for actual cordic algo

	//Print out sin(x) vs fp CORDIC sin(x)
	int main(int argc, char **argv)
	{
	float p;
	// sin_int, cos_in;

	import time
	import numpy as np

	fs_list = [120.0, 2.0]
	dt_list = [1/fs for fs in fs_list]
	prevt_list = [time.time(), ] * len(fs_list)
	sample_times = [list() for fs in fs_list]

	timeout_seconds = 10
	sleep_seconds = min(dt_list) * 0.1

	#include <stdlib.h>
	#include <stdio.h>
	#include <string.h>
	#include <math.h>
	#ifndef NO_LIBSNDFILE
	#include <sndfile.h>
	#endif
	#include "soundpipe.h"

	int sp_create(sp_data **spp)

	import os

	git_version_hook_lines = [
	"#!/bin/sh\n",
	"git_version_str=$(printf '#define GIT_VERSION_STRING \"%s\"' $(git rev-parse --short=16 HEAD))\n",
	"echo $git_version_str\n",
	"echo $git_version_str > ./git_version.h\n",
	]

	hooks_dir = os.path.join(os.getcwd(), '.git', 'hooks')

	# On a normal machine, this should run just fine
	# But some machines require an agressive network security policiy
	# And this simple test will fail

	using Sockets

	TEST_PORT = 12567

	# Listen asynchronously
	listen_task = @async begin