# UART Protocol

If enabled using the `TODO` feature flag, all received messages are transmitted on UART using the protocol described in this document.
The serial communication can also be used to send V2X data.

## Message Format

The UART communication is using a custom framing protocol to encapsulate binary messages.
The payload is:

- a `SerialOutputMsg` for transmissions from the ESP to the host or
- a `SerialInputMsg` for transmissions from the host to the ESP

in binary [Proto](https://protobuf.dev/) serialization according to the [c_its-messages.proto](./c_its-messages.proto) definition.

Each transmission:
- starts with a Start of Frame (SOF) sequence: `0x56, 0x32, 0x58, 0x2B` ("V2X+")
- followed by a 16-bit big-endian length field
- followed by the payload
- followed by an End of Frame (EOF) sequence `0x0d, 0x0a`