TS-4900 RTC
From embeddedTS Manuals
We include the Intersil ISL12020 RTC onboard. This provides an exceptionally long RTC battery life, as well as a built in temperature sensor to provide +- 5ppm across -40 to 85C. This is accessed using /dev/rtc0 in our images, and is accessed using the standard hwclock command.
This RTC driver is also capable of warning when the RTC voltage begins to drop near its end of life. These messages can be seen in the kernel log (dmesg):
rtc-isl12022 1-006f: voltage dropped below 85%, date and time is not reliable. rtc-isl12022 1-006f: voltage dropped below 75%, date and time is not reliable.