Timer-based Loop Function in Python

This repository contains several test scripts for loop functions:

• timer-loop.py loops at a user-defined frequency (default: 100 Hz) using threading.Timer()
• signal-loop.py loops at a user-defined frequency (default: 100 Hz) using signal.setitimer() and a signal.SIGALRM handler function

The two methods are also tested to send control commands and read the position feedback with a brushless DC motor controller (i.e., the ODrive v3.6 by ODriveRobotics).

Benchmark

threading.Timer() was found to be less accurate (i.e., running at a lower frequency compared to what set by the user) w.r.t. signal.setitimer(), both on a general purpose Linux kernel and on a Preempt-patched Linux Kernel. In fact, the Preempt RT patch does not seem to make any difference, even when setting the NICE value of the process to -20 with os.nice(-20).

threading.Timer() results

Target Frequency [Hz]	Delta Time [s]	Actual Frequency [Hz]	Error [%]
1	1.001179	0.9988	0.12
10	0.100716	9.9289	0.71
100	0.010226	97.7870	2.22
150	0007223	138.4480	7.67

signal.setitimer() results

Target Frequency [Hz]	Delta Time [s]	Actual Frequency [Hz]	Error [%]
1	1.000167	0.9998	0.02
10	0.100105	9.9895	0.10
100	0.010025	99.7482	0.25
150	0.006691	149.4595	0.36
1000	0.001004	996.1075	0.39