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Handling Time in Firmware

Authors:
Geoffrey Hunter
Geoffrey Hunter
Published On:
Sep 30, 2024
Last Updated:
Sep 30, 2024

If writing the firmware in C, you’ll likely want to leverage the features provided by time.h.

Here are some of the ways that firmware can keep track of the time:

  • Count the mains power AC cycles to keep track of the time.
  • Use a RTC.
  • Download the time from an internet server.
  • Use a GPS receiver.

mktime

mktime() is used to convert from broken-down time to a UNIX time (time since Epoch). It ignores the weekday (tm_wday) and yearday (tm_yday) fields when converting (as this is redundant information)1.

Real-time Clocks (RTC)

Real-time clocks (RTC) are low-power devices that maintain an accurate time even when the primary power source is interrupted. They usually accept a secondary power source (e.g. coin-cell battery) to ensure they keep running when the primary power source is not available.

Footnotes

  1. The Open Group (2004). mktime - convert broken-down time into time since the Epoch. Retrieved 2024-09-30, from https://pubs.opengroup.org/onlinepubs/009695399/functions/mktime.html. ↩