Instead of wrapping the memory functions in the link stage, rebuild
Newlib and enable retargetable locks. Override the weak definitions
in the libc.a with our own, SDK based ones.
The wrapping utilized before catches app-level memory allocations
but misses allocations inside Newlib libc (like printf/etc.).
Each core needs its own _impure_ptr or else crashes like the one seen
in parallel printf_floats can happen. Enable it in the toolchain
build and implement a simple swapper here.
FreeRTOS SMP doesn't support Newlib's dynamic reent which is needed
to allow save MT support. Minor patch to FreeRTOS and update the
FreeRTOS variant.cpp and setup to support it.
Use low power WFE when idle.
Set PORT.C to built `-O0` always because it seems to occasinally end
up with interrupts disabled in task code, causing the SYSTICK never to
fire and killing task switching.
No need for dynamic exceptions. We don't move the execbase.
Using all the work from @hfellner and others, add FreeRTOS
SMP support.
Allow idling cores through the FreeRTOS FIFO queue to
allow for file system and EEPROM support.
Make delay a weak function so FreeRTOS can override.
Add cycle count support under FreeRTOS using a PIO SM.
Use a task-based approach for handling the USB periodic work
instead of the IRQ-based one in the main core.
Set 8 prio levels so it fits in 3 bits nicely (0..7).
Earle F. Philhower, III