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Message Format
All packets are in the CRSF format [sync] [len] [type] [payload] [crc8] with a maximum total size of 64 bytes.
All serial CRSF packets begin with the CRSF SYNC byte 0xC8, with the exception of EdgeTX's outgoing channel/telemetry packets, which begin with 0xEE. Due to this, for compatibility, new code should support either for the SYNC byte, but all transmitted packets MUST begin with 0xC8. I2C CRSF packets begin with a CRSF address.
Length of bytes that follow, including type, payload, and CRC (PayloadLength+2). Overall packet length is PayloadLength+4 (sync, len, type, crc), or LEN+2 (sync, len).
CRSF_FRAMETYPE. See Packet Types Examples:
- CRSF_FRAMETYPE_LINK_STATISTICS = 0x14
- CRSF_FRAMETYPE_RC_CHANNELS_PACKED = 0x16
- CRSF_FRAMETYPE_DEVICE_PING = 0x28
- CRSF_FRAMETYPE_DEVICE_INFO = 0x29
Data specific to the frame type. Maximum of 60 bytes.
CRC8 using poly 0xD5, includes all bytes from type (buffer[2]) to end of payload.
[sync] [len] [type] [[ext dest] [ext src] [payload]] [crc8]
To support tunneling of packets through the CRSF protocol to remote endpoints, there is an extended packet format, which includes an extended dest and source as part of the payload (see CRSF Addresses for a list). In this case, the LEN field is actually PayloadLength+4, as the first two bytes are the extended dest and source. Maximum payload length is therefore 58 bytes for extended packets.
All packet types CRSF_FRAMETYPE 0x28 and higher use Extended Packet Format.