CanServo/Protocol/LongMessage

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• Up page: CanServo/Protocol/0

Long Message

• A method of sending a long message by dividing it into multiple packets.
  • Of course, 1 packet is also possible.

• This content refers to the message format of UAVCAN.
  • Thanks to UAVCAN

• Note:
  • CRC16 : byte order : low byte first, little endian

• Reference:
  • Code/CRC16

• Transmission method
  • Check the length of the message to be sent, and if it cannot be sent in one packet, calculate CRC16 and add it to the end of the message.
    • The starting value for CRC16 calculation is 0xFFFF (-1).
  • Repeat the process of cutting from the front, attaching the Tail Byte, and sending it as one packet.
    • At this time, if the length (including Tail Byte) exceeds 8 bytes, the exact length is placed in the first byte.
  • NOTE: If it is not an FD, the maximum is 8 bytes, so it can be up to 7 bytes.
    • In the case of FD, the maximum is 64 bytes, so excluding the first byte of length, it can be up to 62 bytes.

• 주의 사항
  • Host가 발신하는 경우는, 동시에 전송하지 않으면 되지만,
  • 서보가 보내는 경우는, 여러 서보가 동시에 보낼 수 있습니다.
  • 같은 CAN ID 로 동시에 여러 Long Message가 전송 될 때에는, Tail Byte 의 변화와 CRC16 등으로 분석합니다.

CAN-FD

• CAN-FD data is expanded up to 64 bytes.
  • 0~8, 12, 16, 20, 24, 32, 48, 64

• CanServo/Protocol/CAN-FD

Tail Byte

• Tail Byte
  • bit 7 = first packet
  • bit 6 = last packet
  • bit 5 = 1 if first packet, toggle bit on each packet
  • bit 4:0 = Seq, 0 ~ 31, inc 1 on each message