The real-time clock (RTC) resides in the PMC and maintains an accurate time base for system and application software. It includes calibration circuitry to offset temperature and voltage fluctuations in applications requiring greater accuracy. The RTC also provides alarm setting and periodic interrupt features. The real-time clock provides continuous operation powered by the PMC auxiliary supply (VCCAUX_PMC) or the battery supply (VCC_BATT). When the auxiliary supply is available, the RTC uses it to keep the counters active. The RTC automatically switches to the battery power supply when the auxiliary supply is not available.
The RTC generates two system interrupt signals to the generic interrupt controller (GIC), the GIC proxy, and the programmable logic (PL) once every second and when an alarm event occurs. The periodic second tick interrupt can be used by all system processors. The alarm control must be managed at a system level with the processors.
As shown in the following figure, the RTC subsystem has three main modules: counter module, control register module, and oscillator module. The RTC counters module is powered by the battery power domain and includes three counters, calibration circuitry, and logic used to retain the programmed time. The RTC control register module is implemented in the PMC power domain and incorporates all of the registers associated with the RTC controller. The oscillator module is supplied by the battery power domain and provides the RTC clock.
