View Source Porting Elixir/ALE to Circuits.I2C

The Circuits.I2C package is the next version of Elixir/ALE's I2C support. If you're currently using Elixir/ALE, you're encouraged to switch. Here are some benefits:

  1. Supported by both the maintainer of Elixir/ALE and a couple others. They'd prefer to support Circuits.I2C issues.
  2. Much faster than Elixir/ALE.
  3. Simplified API

Circuits.I2C uses Erlang's NIF interface. NIFs have the downside of being able to crash the Erlang VM. Experience with Elixir/ALE has given many of us confidence that this won't be a problem.


Code modifications

Circuits.I2C is not a GenServer, so if you've added ElixirALE.I2C to a supervision tree, you'll have to take it out and manually call to obtain a reference. A common pattern is to create a GenServer that is descriptive of what the I2C device does and have it be responsible for all I2C calls.

The remain modifications should mostly be mechanical:

  1. Rename references to ElixirALE.I2C to Circuits.I2C and elixir_ale to circuits_i2c
  2. Change calls to ElixirALE.I2C.start_link/2 to You'll need to remove the I2C address from the call to open. While you're at it, review the arguments to open to not include any GenServer options.
  3. Add the I2C device's bus address to all of the read, write, and write_read calls. We recommend making a short helper function that has the I2C address.
  4. The read and write_read functions now return {:ok, result} tuples on success so add code to handle that. Alternately, call read! or write_read! and they will raise an exception if there's an error.
  5. Look for calls to I2C.read_device, I2C.write_device and I2C.write_read_device and remove the _device part.
  6. Consider adding a call to Circuits.I2C.close/1 if there's an obvious place to release the I2C. This is not strictly necessary since the garbage collector will free unreferenced I2C references.
  7. If you manually implemented I2C bus retry logic, consider specifying the :retries option to have Circuits.I2C retry for you.
  8. Change calls to ElixirALE.I2C.device_names/0 to Circuits.I2C.bus_names/0.

If you find that you have to make any other changes, please let us know via an issue or PR so that other users can benefit.