Christian Wenzel-Benner presented a German talk / demo with the translated title "Clockdrift in Distributed Embedded Systems" at the Embedded Software Engineering Kongress (ESE) 2023 in Sindelfingen. This is the recorded English version. Clock drift is an annoying source of seemingly arbitrary issues in distributed embedded systems. Data transmission and/or processing fails at seemingly random times while the code looks good and unit tests pass. The driver behind these issues is the deviation of the actual oscillation frequency of "identical" crystals. Take five 8MHz crystals of the same type from the same supplier produced in one batch and they will all oscillate at close to 8MHz, but not precisely. The usual difference within any pair of them will be between 1 and 20 parts per million (ppm). This means that instead of 8.000.000Hz they might run at 8.000.018Hz and 7.999.983Hz. While such a small difference is almost unrecognizable in a bench test (unless specifically looking for it), over time two microcontrollers driven by these crystals will drift apart and eventually data processing between them may fail. Peter Gliwas book Embedded Software Timing (Springer, 2020) explains the mechanism in chapter 6.4 in detail. Our talk/demo video shows the effect of drift over 30 hours using time-lapse recordings and presents methods to compensate for the issue using standard protocols or DIY solutions.
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Book “Embedded Software Timing” by Peter Gliwa:
www.gliwa.com/book/