11.1. About the Real Time Clock

The PrimeCell Real Time Clock (RTC) PL031 is an Advanced Microcontroller Bus Architecture (AMBA) compliant System-on-a-Chip (SoC) peripheral that is developed, tested, and licensed by ARM. The RTC connects to the core APB.

The RTC comprises:

The CPU reads and writes data, and control and status information through the AMBA APB interface.

The 32-bit counter is incremented on successive rising edges of the input clock CLK1HZ. Counting in one second intervals is achieved by using an internal 1Hz clock signal for CLK1HZ. The counter is free-running. On reset, the counter:

RTC is loaded or updated by writing to the load register, RTCLR.

Reading the data register, RTCDR, gives the current value of the RTC.

The match register is programmed by writing to RTCMR. The counter and match values are compared in a comparator. When both values are equal, the interrupt RTCINTR is asserted HIGH. The CPU can use the interrupt to implement a basic time alarm function. The interrupt is cleared by writing any data value to the interrupt clear register RTCICR. The value in the match register can be read at any time.

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