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FreeRTOS_Semaphore_LowPower Application Description

This application demonstrates the use of FreeRTOS tickless low power mode and semaphores.

The system relies on RTC Alarm A to wake up from its low power state. The alarm behavior is configured to occur every second.

The thread blocks on a semaphore which causes the system to enter STOP mode.

Once the alarm is generated using the RTC peripheral, an interrupt is triggered and the CPU returns to RUN mode. The semaphore is released in the RTC's interrupt handler. The thread resumes execution and toggles the green LED.

Expected success behavior

Successful operation is marked by the green LED toggling every second.

Error behaviors

On failure, the green LED is turned off and an error message is printed to the serial port.

Assumptions if any

None

Known limitations

None

Notes

To measure the current consumption remove JP6 jumper and connect an ammeter to JP6 to measure IDD current.

This example can not be used in DEBUG mode due to the fact that the Cortex-M0+ core is no longer clocked during low power mode so debugging features are disabled.

It is possible to reduce power consumption even further by configuring all pins as analog pins and disabling their clocks.

FreeRTOS usage hints

The FreeRTOS heap size configTOTAL_HEAP_SIZE defined in FreeRTOSConfig.h is set accordingly to the OS resources memory requirements of the application with +10% margin and rounded to the upper Kbyte boundary.

For more details about FreeRTOS implementation on STM32Cube, please refer to UM1722 "Developing Applications on STM32Cube with RTOS".

Keywords

FreeRTOS, RTOS, LowPower, RTC, Alarm

Hardware and Software environment

  • This application runs on STM32C031C6Tx devices.

  • This application has been tested with STMicroelectronics NUCLEO-C031C6 board MB1717 Rev. B01 and can be easily tailored to any other supported device and development board.

  • This application uses USART2 to display output, the hyperterminal configuration is as follows:

    • BaudRate = 115200 baud
    • Word Length = 8 Bits
    • Stop Bit = 1
    • Parity = none
    • Flow control = None

How to use it ?

In order to make the program work, you must do the following :

  • Open the project in your preferred toolchain
  • Rebuild all files and load your image into target memory
  • Run the application