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).