The RTC module was introduced in RISC OS 5.21. It acts as a common point of access to the hardware RTC. The module is also in charge of any fine-tuning of the clock. The default behaviour is to keep the soft clock synchronised to the hardware RTC, but software can use the RTC_Adjust SWI to request other corrections.
Internally, the module uses a RTC HAL device in order to communicate with the RTC hardware.