Peripheral Clock Gating; Sleep Mode - STMicroelectronics STM32F05 series Reference Manual

Power control (PWR)
6.3.2

Peripheral clock gating

In Run mode, the HCLK and PCLK for individual peripherals and memories can be stopped
at any time to reduce power consumption.
To further reduce power consumption in Sleep mode the peripheral clocks can be disabled
prior to executing the WFI or WFE instructions.
Peripheral clock gating is controlled by the
(RCC_AHBENR), the
APB1 peripheral clock enable register
6.3.3

Sleep mode

Entering Sleep mode
The Sleep mode is entered by executing the WFI (Wait For Interrupt) or WFE (Wait for
Event) instructions. Two options are available to select the Sleep mode entry mechanism,
depending on the SLEEPONEXIT bit in the Cortex-M0 System Control register:
●
Sleep-now: if the SLEEPONEXIT bit is cleared, the MCU enters Sleep mode as soon
as WFI or WFE instruction is executed.
● Sleep-on-exit: if the SLEEPONEXIT bit is set, the MCU enters Sleep mode as soon as
it exits the lowest priority ISR.
In the Sleep mode, all I/O pins keep the same state as in the Run mode.
Refer to
Exiting Sleep mode
If the WFI instruction is used to enter Sleep mode, any peripheral interrupt acknowledged by
the nested vectored interrupt controller (NVIC) can wake up the device from Sleep mode.
If the WFE instruction is used to enter Sleep mode, the MCU exits Sleep mode as soon as
an event occurs. The wakeup event can be generated either by:
●
enabling an interrupt in the peripheral control register but not in the NVIC, and enabling
the SEVONPEND bit in the Cortex-M0 System Control register. When the MCU
resumes from WFE, the peripheral interrupt pending bit and the peripheral NVIC IRQ
channel pending bit (in the NVIC interrupt clear pending register) have to be cleared.
●
or configuring an external or internal EXTI line in event mode. When the CPU resumes
from WFE, it is not necessary to clear the peripheral interrupt pending bit or the NVIC
IRQ channel pending bit as the pending bit corresponding to the event line is not set.
This mode offers the lowest wakeup time as no time is wasted in interrupt entry/exit.
Refer to
72/742
APB2 peripheral clock enable register (RCC_APB2ENR)
Table 14 and Table 15
Table 14 and Table 15
Doc ID 018940 Rev 1
AHB peripheral clock enable register
(RCC_APB1ENR).
for details on how to enter Sleep mode.
for more details on how to exit Sleep mode.
RM0091
and the