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FreeRTOS™ Code Revisions - Background Worker Edition brad
Down the Rabbit Hole

As part of our commitment to the open source community, Pebble is releasing its recent modifications to the FreeRTOS project. Pebble has made a few minor changes to FreeRTOS to enable Background Workers for PebbleOS 2.6 as well as to make Pebble easier to monitor and debug.

The changes are available as a tarball.

Below is a changelog of the modifications since the last time we released our fork of the FreeRTOS code back in May.

  • Added UBaseType_t uxQueueGetRecursiveCallCount( QueueHandle_t xMutex ) PRIVILEGED_FUNCTION; to queue.h

    • Retrieves the number of times a mutex has been recursively taken
    • FreeRTOS always tracked this internally but never made it available externally
    • Used to debug locking relating issues in PebbleOS

  • Added configASSERT_SAFE_TO_CALL_FREERTOS_API();

    • This macro can be used to assert that it is safe to call a FreeRTOS API. It checks that the caller is not processing an interrupt or in a critical section.
    • See http://www.freertos.org/RTOS-Cortex-M3-M4.html for more details on how interrupts interact with the FreeRTOS API

  • Added configASSERT_SAFE_TO_CALL_FREERTOS_FROMISR_API();

    • This macro can be used to assert that it is safe to call a FreeRTOS "FromISR" API. It checks that the caller is at an appropriate interrupt level.
    • See http://www.freertos.org/RTOS-Cortex-M3-M4.html for more details on how interrupts interact with the FreeRTOS API

  • Added uintptr_t ulTaskGetStackStart( xTaskHandle xTask ); to task.h

    • Retrieves the address of the start of the stack space
    • Useful for implementing routines which check for available stack space

  • Added bool vPortInCritical( void ); to port.c

    • Indicates if we're currently in a FreeRTOS critical section
    • Used to implement configASSERT_SAFE_TO_CALL_FREERTOS_API();

  • Fixed an issue with vPortStoreTaskMPUSettings that occurred when more than one task wanted to configure MPU regions

    • This bug was encountered when adding support for Background Workers in FW 2.6

Pebble would like to again extend its thanks to FreeRTOS and its community. We'll be releasing additional updates as we continue to modify FreeRTOS in the future. If you have any questions, don’t hesitate to contact us.