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FreeRTOS_MPU Application Description

This application demonstrates the use of the MPU with FreeRTOS to control memory/peripheral access for tasks. It implements simple recovery mechanisms from prohibited memory accesses. The application creates one Privileged mode task using xTaskCreate():

  • 'MainTask': Has higher priority than the unprivileged tasks. Blocks while waiting for a fault to occur. Displays information about the faults and takes corrective actions. It also has User mode tasks created using the xTaskCreateRestricted() API:

  • 'Task1': Has read only access to shared memory Attempts an illegal write to the shared memory only once Toggles the green LED

  • 'Task2': Has read only access to shared memory Attempts an illegal write to the shared memory periodically Toggles the yellow LED The application will try to recover from MemManage fault exception for each task until EXAMPLE_FAULT_COUNT_THRESHOLD is reached for that task. At that point the task will be suspended to avoid further exceptions.

Expected success behavior

Successful operation is marked by a toggling green led light. The yellow LED will toggle EXAMPLE_FAULT_COUNT_THRESHOLD times. Information about the faults will be printed to the serial port.

Error behaviors

On failure, the red led is ON.

Assumptions if any

None

Known limitations

None

Notes

1- When used with the MPU, FreeRTOS requires various regions to be defined in the linker file. For more information, refer to the linker files in the example as well as the FreeRTOS Documentation/Blog:

https://freertos.org/2020/04/using-freertos-on-armv8-m-microcontrollers.html#FREERTOS_WITH_MPU

2- MPU regions are required to have a size which is a multiple of 32 bytes and to be aligned on the 32 byte boundary. In particular, unprivileged task stacks must comply with these requirements.

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, MPU, Threading

Hardware and Software environment

  • This application runs on STM32H563xx devices.
  • This application has been tested with STMicroelectronics NUCLEO-H563ZI board MB1404 Rev. B02 and can be easily tailored to any other supported device and development board.
  • This application uses USART3 to display logs, 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