DocID025303 Rev 2

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AN4365

STM32F4 low-power application case

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Sensor (Slave) state machine

Run1_S: system clock configuration

Sleep1: DMA samples transfer to memory during CPU Sleep mode

Run3_S: I2C and DMA configurations and start of data transmission to the sensor hub

Sleep2: DMA samples transfer from Sensor to Master via I2C during CPU Sleep mode

Run4_S: clearing of DMA pending flags on transmitter stream

Stdby: once operations are finished, the sensor CPU enters in Standby mode waiting for a

request from the Master to wake-up again.

Debug mode

By default, the debug connection is lost if the application puts the MCU in Standby, for

example. This is due to the fact that the CPU is no longer clocked.

However, by setting some configuration bits in the DBGMCU_CR register, the software can

be debugged even when using the low-power modes extensively. This is done by

uncommenting #define DEBUG in main.h

Auto-wakeup

The RTC (clocked by LSI ~32 KHz) provides a programmable time base for waking-up the

sensor hub from Standby mode at regular intervals (~200 ms).

Note:

To follow the functional behavior of this application, the user has to visualize signals with an

oscilloscope or go in Debug mode.

3.1.2

Firmware architecture description

This application uses the STM32F4 library and contains the following main source files:

•

main.c: contains the overall needed functions for the application

•

STM32F4_it.c: contains the interrupt handlers for the application

•

STM32F4_system.c: contains the system clock configuration for the STM32F4

devices used in the application