atsamd21 support for Rust

This repo holds various things that support/enable working with atmel samd21 based devices, such as the Adafruit Metro M0, Trinket M0 and Gemma M0, using Rust.

There are a couple of crates provided by this repo:

atsamd21g18a is an auto-generated crate providing access to the peripherals specified for this device by its SVD file. This is the MCU used in the Metro M0, Feather M0 and Circuit Playground express boards from Adafruit.
atsamd21e18a is an auto-generated crate providing access to the peripherals specified for this device by its SVD file. This is the MCU used in the Trinket M0 and Gemma M0 boards from Adafruit.
atsamd21-hal is the result of reading the datasheet for the device and encoding a type-safe layer over the raw atsamd21g18a and atsamd21e18a crates. This crate implements traits specified by the embedded-hal project, making it compatible with various drivers in the embedded rust ecosystem.
metro_m0 is a board support crate for the Adafruit Metro M0 board. It re-exports the atsamd21-hal crate functionality using more convenient names; for example, the IO pins are exported using the labels printed on the board rather than the more abstract and harder to remember port and pin numbers used by the underlying device.
gemma_m0 is a board support crate for the Adafruit Gemma M0 board. Similar to the Metro M0 crate, it re-exports the atsamd21-hal crate functionality using more convenient names.

Building

The atsamd21 devices require untagged union support which means that you will need to be using nightly rust. You'll also need to install support for thumbv6m-none-eabi:

$ rustup install nightly
$ rustup default nightly
$ rustup target add thumbv6m-none-eabi

Since a couple of different MCUs are used, building the examples requires changing directory into one of the board support crate dirs prior to building:

$ cd metro_m0
$ cargo build --examples
$ cd ../gemma_m0
$ cargo build --examples

Getting code onto the device: Gemma M0

If you want to flash the device using the tools that come with the adafruit arduino support package:

$ cd gemma_m0
$ cargo build --example blinky_basic
$ arm-none-eabi-objcopy -O binary \
  target/thumbv6m-none-eabi/debug/examples/blinky_basic \
  target/thumbv6m-none-eabi/debug/examples/blinky_basic.bin
$ stty -F /dev/ttyACM1 ospeed 1200
$ ~/.arduino15/packages/arduino/tools/bossac/1.7.0/bossac -i -d \
  --port=ttyACM1 -U true -i -e -w -v \
  target/thumbv6m-none-eabi/debug/examples/blinky_basic.bin -R

This same technique should work for all of the Adafruit M0 boards, as they all ship with a bossac compatible bootloader.

Getting code onto the device: JLink

If you have a board with a SWD debug header, such as the Metro M0, or if you attached the header yourself, you can use your JLink together with gdb. @wez prefers using the JLinkGDBServer, but you can also use OpenOCD.

In one window, run JLinkGDBServer -if SWD -device ATSAMD21G18, then in another, run these commands from the root of this repo so that you pick up its .gdbinit file:

$ cargo build --manifest-path metro_m0/Cargo.toml --example blinky_basic
$ arm-none-eabi-gdb metro_m0/target/thumbv6m-none-eabi/debug/examples/blinky_basic

If you prefer or otherwise need to use OpenOCD, then you'd run it in place of the JLinkGDBServer and then modify the .gdbinit file to comment out the JLink section and uncomment the OpenOCD section.

Semihosting

If you want to enable semihosting to be able to see debugging messages, this will enable them in some of the example crates. Note that when you enable semihosting, the resultant firmware will only run when a debugger is attached to your board; it will fault the MCU if the debugger is absent:

$ cargo build --manifest-path metro_m0/Cargo.toml \
  --example blinky_basic --features use_semihosting

License

The included SVD files are sourced from http://packs.download.atmel.com/ and are licensed under the Apache License, Version 2.0 (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0).

The remainder of the code is licensed under either of:

Apache License, Version 2.0 (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)

at your option.

Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.