FortyTwo Systems has assembled a full toolchain for compiling software targeted at the SAMC21/SAMC21N. The toolchain consists of the following components:
ArduinoModule-CMSIS-Microchip: Microchip vendor-specific ARM CMSIS package. Pulled from Microchip packs. Includes support for a variety of popular processors.
ArduinoModule-CMSIS: ARM CMSIS package, with DSP modules pre-compiled for Cortex-M0+
ArduinoModule-gcc-arm-none-eabi: Latest ARM GCC compiler, with custom built version for ARM32 (rpi) architecture. Latest Arduino version is at least 4 years old (!)
BOSSAC: tool that is used to flash firmware onto SAM microcontrollers via the bootloader. Custom version with support for SAMC21 processors.
Additionally, FortyTwo Systems maintains a full configuration for PlatformIO: