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RTC Diagnostics and FAQ

  • Time returns to a fixed value after reboot: inspect backup power, the 32 kHz crystal, and RTC-domain retention.
  • Time does not advance: inspect oscillator, clock source, reset, and probe log.
  • System time is correct but RTC is wrong: run hwclock -w and check write permissions.
  • RTC is correct but system time is wrong: inspect CONFIG_RTC_HCTOSYS, the selected hctosys device, and Android time services.
  • Time gradually drifts: measure daily error and inspect crystal loading and temperature.
dmesg | grep -i rtc
cat /sys/class/rtc/rtc0/name
cat /sys/class/rtc/rtc0/since_epoch

General diagnostic order​

  1. Schematic and power.
  2. Node and pinctrl in the final DTB.
  3. Final .config and modules.
  4. Probe, clock, reset, and IRQ logs.
  5. Device node and sysfs/debugfs.
  6. Minimal functional test.
  7. Stress, suspend, and abnormal hot-plug tests.

Do not treat the removal of an error log as a fix. Find the first failure and validate its upstream and downstream dependencies.