RTC support in the Letux 400.
Real-time clock (RTC) support in the Letux 400 relies on use of the PCF8563 RTC chip found on the system board. See: https://www.nxp.com/docs/en/data-sheet/PCF8563.pdf
There is an RTC peripheral in the JZ4730 which has core registers similar to those of the JZ4740, but the peripheral appears to lack the hibernation-related registers.
Consequently, RTC operations involve I2C transactions with I2C address 0x51.
In modern kernels the following files are pertinent: