2.5.5.3 The Wakeup Interrupt Controller

The Wakeup Interrupt Controller (WIC) is a peripheral that can detect an interrupt and wake the processor from deep sleep mode. The WIC is enabled only when the DEEPSLEEP bit in the SCR is set to 1, see 2.7.2.6 System Control Register.

The WIC is not programmable, and does not have any registers or user interface. It operates entirely from hardware signals.

When the WIC is enabled and the processor enters deep sleep mode, the power management unit in the system can power down most of the Cortex-M3 processor. This has the side effect of stopping the SysTick timer. When the WIC receives an interrupt, it takes a number of clock cycles to wakeup the processor and restore its state, before it can process the interrupt. This means interrupt latency is increased in deep sleep mode.