This saves a lot of RAM. Fixes#287.
Also fixed compilation of frozen_mpy.c to use supplied make rule rather than
builtin rule (supplied rule suppresses printing out the gcc command line).
* atmel-samd: Introduce a nvm module for non-volatile byte-level memory access.
This allows for persisting small configuration values even when the file system
is read-only from CircuitPython.
Fixes#160
* Review feedback:
* Add tests.
* Fix non-zero index.
* Fix len()
Reworked frozen module support: clean up makefiles and handle multiple directories.
Modules to freeze are included as git submodules.
Add neopixel to circuitplayground express build.
Fixes#56
* Reset SWD lines to SWD rather than GPIO. This makes OpenOCD happier.
* Default speaker enable lines to False for CircuitPlayground to prevent
the speaker from buzzing when no sound is playing. Fixes#126
Also replace use of PINMUX_DEFAULT with PINMUX_UNUSED to prevent any
accidental pin changes. This caused user SPI to break internal SPI
flash on the Feather M0 Express.
Fixes#100
