PL031 RTC is an Advanced Microcontroller Bus Architecture (AMBA) slave module that connects to the Advanced Peripheral Bus (APB) used provide a basic alarm function or long time base counter. A 32-bit free-running counter is incremented on successive rising edges of the 1Hz clock signal input. The counter and match values are compared in a comparator which triggers a maskable interrupt that can be used to implement a basic time alarm function.