1. Article purpose[edit source]
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 source]
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.
| Level | Mode | Vddcore state | Clocks state |
|---|---|---|---|
| Subsystem | MPU CRun | on | on |
| MPU CStop | on | Subsystem off | |
| MPU CStandby | on | Subsystem off | |
| MCU CRun | on | on | |
| MCU CStop | on | Subsystem off |
| MPU mode | MCU mode | Platform mode | Vddcore state | Clocks state |
|---|---|---|---|---|
| CRun | CRun | Run | On | On |
| CStop | CRun | Run | On | On |
| CStandby | CRun | Run | On | On |
| CRun | CStop | Run | On | On |
| CStop | CStop | Stop/LPLV-Stop/Standby | On/Retention/Off | Off/Off/Off |
| CStandby | CStop | Stop/LPLV-Stop/Standby | On/Retention/Off | Off/Off/Off |
2.1. Wakeup sources[edit source]
The above modes are left due to a wakeup event. It can be configured by setting the wakeup control feature of the IP and activating the corresponding EXTI on MCU side.
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 source]
The power HAL is used to select the Cortex-M4 low power mode. The MPU uses the Linux® RPMsg framework to communicate with the MCU.
Further information on HAL can be found here: STM32CubeMP1 architecture
3.1. APIs description[edit source]
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
3.2. Code source location[edit source]
STM32CubeMP1 Package provides power HAL driver:
Drivers/STM32MP1xx_HAL_Driver/Src/stm32mp1xx_hal_pwr.c