The 16k FreeRTOS heap originally had all TCBs and stacks dynamically
allocated within it (plus semaphores and some other things). Now that
xTaskCreateStatic is used instead of xTaskCreate, the TCBs and stacks
are allocated statically and no longer use any of the FreeRTOS heap.
Therefore, the FreeRTOS stack can be shrunk by the amount that has been
made static. Furthermore, the TCBs and stack that are now static should
be placed in the .rtos_heaps section of RAM because this RAM is treated
specially by the bootloader (the bootloader executes from the first 16k
of RAM and loads the firmware into the section starting after the 16k).
After this patch the FreeRTOS heap (ucHeap) is 7200 bytes. The memory
available for the MicroPython heap is 54936 bytes (including GC overhead).
In VStartSimpleLinkSpawnTask we change xTaskCreate to xTaskCreateStatic
so that the task is created using statically allocated memory for the TCB
and stack.
This means that xTaskCreate function is no longer needed (the static
version is now used exclusively).
This function is no longer used. Having the .boot section attribute
meant that it was included in the firmware regargless of use. Without
this attribute the linker can remove the function.
This allows to statically allocate the TCB (thread control block) and
thread stack in the BSS segment, reducing the need for dynamic memory
allocation.
Now only the bits that really need to be written in assembler are written
in it, otherwise C is used. This means that the assembler code no longer
needs to know about the global state structure which makes it much easier
to maintain.
This is a pristine copy (actually a subset of files) of upstream FreeRTOS
v9.0.0.
Modifications to the previous version of FreeRTOS (v8.1.2) included
addition of __attribute__ ((section (".boot"))) to the following
functions:
pxPortInitialiseStack
prvTaskExitError
prvPortStartFirstTask
xPortStartScheduler
vPortSetupTimerInterrupt
xTaskGenericCreate
vTaskStartScheduler
prvInitialiseTCBVariables
prvInitialiseTaskLists
prvAllocateTCBAndStack
This attribute will need to be reinstated on a case-by-case basis
because some of the above functions are now removed/changed.
Damien George