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CRSF_FRAMETYPE_COMMAND

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Bryan Mayland edited this page Mar 13, 2024 · 16 revisions

Command

Commands are sent using extended CRSF_FRAMETYPE_COMMAND (0x32) type packets. The variable-length payload [realm] [cmd payload] [crc8-ba] includes a single byte command type/id/realm, and any data needed for the command, followed by a second CRC. The additional crc8-ba is CRC8 using poly 0xBA and includes all bytes from type (buffer[2] = CRSF_FRAMETYPE_COMMAND), including the extended header, to the end of payload.

Extended payload

  • uint8_t command_realm
  • uint8_t subcommand / cmd_payload[]
  • uint8_t crc8-ba. NOTE: Many existing implementations omit this field on some packets. Transitional parsers SHOULD allow command packets without this second CRC to pass as if they do and the CRC was correct.

Typically command realm is followed by the subcommand making the extended payload [realm] [subcmd] [payload] [crc8-ba].

Command Realms

Realm (Hex / Decimal) Enum Description
0x10 / 16 CRSF_COMMAND_SUBCMD_RX Receiver
0x0A / 10 CRSF_COMMAND_SUBCMD_GENERAL General

CRSF_COMMAND_SUBCMD_RX

Command (Hex / Decimal) Enum Description
0x01 / 1 CRSF_COMMAND_SUBCMD_RX_BIND Enter binding mode
0x05 / 5 COMMAND_MODEL_SELECT_ID Set Receiver / Model ID

CRSF_COMMAND_SUBCMD_RX_BIND

Requests the target device enter bind mode / send a bind information / complete binding. This is the command sent by the Betaflight Configurator "Bind RX" button for UART CRSF receivers.

  • ExpressLRS - (>=3.4.0) A packet with extended destination CRSF_ADDRESS_CRSF_RECEIVER received by the receiver will put the receiver into binding mode. Destination of CRSF_ADDRESS_CRSF_TRANSMITTER received by the transmitter module will broadcast the binding phrase to complete binding.
  • TBS - ??

COMMAND_MODEL_SELECT_ID

The ReceiverID is stored on the handset and passed to the transmitter module when a connection to it is established, which must be prior to the module establishing a connection to the receiver. This is done using an extended CRSF_FRAMETYPE_COMMAND (0x32) type packet with command realm RX (0x10) and command COMMAND_MODEL_SELECT_ID (0x05).

Example: Set ReceiverID to 54 (0x36) c8 08 32 ee ea 10 05 36 26 a0.

CRSF_COMMAND_SUBCMD_GENERAL

Command (Hex / Decimal) Enum Description
0x70 / 112 CRSF_COMMAND_SUBCMD_GENERAL_CRSF_SPEED_PROPOSAL (CRSFv3) Proposed new CRSF port speed
0x71 / 113 CRSF_COMMAND_SUBCMD_GENERAL_CRSF_SPEED_RESPONSE (CRSFv3) response to the proposed CRSF port speed

CRSF_COMMAND_SUBCMD_GENERAL_CRSF_SPEED_PROPOSAL

  • uint8_t port id - ID of this request, used for response
  • uint32_t proposed baud rate (Big Endian)
    • e.g. 416666bps sent as 0x00065B9A / 416666
    • e.g. 5.25Mbps sent as 0x00501BD0 / 5250000

CRSF_COMMAND_SUBCMD_GENERAL_CRSF_SPEED_RESPONSE

  • uint8_t port id - port ID sent in CRSF_COMMAND_SUBCMD_GENERAL_CRSF_SPEED_PROPOSAL command
  • uint8_t accept - 0 if the new baud rate is not acceptable, 1 if the baud rate is accepted and baud rate will change shortly
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