PM0056 datasheet(44/156 Pages) STMICROELECTRONICS

44 / 156 page

The Cortex-M3 processor

PM0056

44/156

DocID15491 Rev 5

Wakeup from WFE

The processor wakes up if:

•

it detects an exception with sufficient priority to cause exception entry

•

it detects an external event signal, see The external event input on page 44

In addition, if the SEVONPEND bit in the SCR is set to 1, any new pending interrupt triggers

an event and wakes up the processor, even if the interrupt is disabled or has insufficient

priority to cause exception entry. For more information about the SCR see System control

2.5.3

The external event input

The processor provides an external event input signal. This signal can be generated by the

up to 16 external input lines, by the PVD, RTC alarm or by the USB wakeup event,

configured through the external interrupt/event controller (EXTI).

This signal can wakeup the processor from WFE, or set the internal WFE event register to

one to indicate that the processor must not enter sleep mode on a later WFE instruction, see

Wait for event on page 43. Fore more details please refer to the STM32 reference manual,

section 4.3 Low power modes.

2.5.4

Power management programming hints

ANSI C cannot directly generate the WFI and WFE instructions. The CMSIS provides the

following intrinsic functions for these instructions:

void __WFE(void) // Wait for Event

void __WFE(void) // Wait for Interrupt

PM0056 Datasheet(PDF) 44 Page - STMicroelectronics