Coprocessor power management

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1 Article purpose[edit]

The purpose of this article is to give an overview of the software APIs available on the Arm® Cortex®-M4 (also named MCU) side to handle the low power modes.

2 Low power modes available on the chip[edit]

Refer to STM32MP15 reference manuals for the full description of the modes.
The AN5109 low power application note also gives details on these modes.

The modes are handled by RCC and PWR peripherals.

The table below explains the chip hardware states corresponding to each low power mode.

Subsystem either refers to Arm® Cortex®-A7 side (also called MPU) or Arm® Cortex®-M4 side (also called MCU). A mode prefixed by 'C' refers to a subsystem mode.

A platform mode is the combination of MPU and MCU modes.

Mode Vddcore state Clocks state
MCU CRun on on
MCU CStop on Subsystem off

2.1 Wakeup sources[edit]

The above modes are left due to a wakeup event.

The following table gives the list of wakeup sources available in each mode.

Mode Available wakeup sources
CStop/CStandby/Stop BOR, PVD, AVD, Vbat mon, Temp mon, LSE CSS, RTC, TAMP, USB, CEC, ETH, USART, I²C, SPI, LPTIM, IWDG, GPIO, Wakeup pins
LPLV-Stop BOR, PVD, AVD, Vbat mon, Temp mon, LSE CSS, RTC, TAMP, IWDG, GPIO, Wakeup pins
Standby BOR, Vbat mon, Temp mon, LSE CSS, RTC, TAMP, IWDG, Wakeup pins

3 Software overview[edit]

The power HAL is used to select the Cortex-M4 low power mode.

Further information on HAL can be found here: STM32CubeMP1 architecture

3.1 APIs description[edit]

The power HAL supports the following APIs related to power management:

 HAL_PWR_EnterSLEEPMode: CSleep mode is entered
 HAL_PWR_EnterStopMode: CStop mode is entered allowing Stop as the deepest platform low power mode 
 HAL_PWR_EnterStandbyMode: CStop mode is entered allowing Standby as the deepest platform low power mode