* * Harden stdio_usb and stdio in general against deadlocks which could otherwise result from doing printfs from within IRQs
* Add a test for the above
* Add mutex_try_enter_block_until API.
* Make best_effort_wfe_or_timeout not use alarms if called from within IRQ
Adds a new cmsis_core INTERFACE library, which provides the basic CMSIS macros/definitions, and RP2040.h and system_RP2040.h
By default the isr_ methods in the vector table are renamed to their CMSIS versions, but this can be overridden by defining PICO_CMSIS_RENAME_EXCEPTIONS=0
