BearBus is a message protocol intended for use on UART and similar interfaces. It allows for communication between a single host and up to 127 devices using
up to 60 command codes.
Messages can contain up to 240 bytes of extra data which is either CRC-8 (up
to 13 bytes of data) or CRC-16 verified (14-240 bytes). The total message
length is thus between 5 bytes (a single data byte) and 247 bytes (5 byte
header, 240 bytes data, 2 bytes CRC-16).
All commands either originate from host or have host as their destination.
There is no inter-device communication.
There are three distinct versions of packet:
- Short (only 5-byte header with a single byte of embedded data)
- Basic (up to 13 bytes of data are supported)
- Long (up to 240 bytes of data are supported)
Packet is defined as follows:
| Bit | ||||||||
|---|---|---|---|---|---|---|---|---|
| Octet | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
| 0:1 | Header (0xBB) | |||||||
| 1:1 | Origin | Address | ||||||
| 2:1 | Reply/Error | EmbedData | CommandCode | |||||
| 3:1 | DataLength EmbedData=0 | |||||||
| 3:1 | Datum EmbedData=1 | |||||||
| 4:1 | HeaderCRC8 | |||||||
| 5:N | Data EmbedData=0 | |||||||
| 5+N:1 | DataCRC8 EmbedData=0, DataLength<=13 | |||||||
| 5+N:2 | DataCRC16 EmbedData=1, DataLength>13 | |||||||
More details available on GitHub.