Drogue IoT Grove SPI over UART

This crate implements an SPI interface over UART, as used by Grove's LoRaWAN board.

lib.rs:

SPI over UART

The UARTSPI struct implements an SPI interface on top of a UART, using the protocol used by Grove.

Also see: https://github.com/Seeed-Studio/Grove_LoRa_433MHz_and_915MHz_RF/blob/master/examples/Grove_LoRa_firmware/Grove_LoRa_firmware.ino

Protocol

When writing, this is:

| 'W' | <reg> | <len> | <data>... |

There is no response after a write request has been processed.

When reading, it is:

| 'R' | <reg> | <len> |

This will follow bytes, which is the data read from SPI.