inav/docs/development/msp/format.md

Format:

JSON format example:

    "MSP_API_VERSION": {
        "code": 1,
        "mspv": 1,
        "request": null,
        "reply": {
            "payload": [
                {
                    "name": "mspProtocolVersion",
                    "ctype": "uint8_t",
                    "units": "",
                    "desc": "MSP Protocol version (`MSP_PROTOCOL_VERSION`, typically 0)."
                },
                {
                    "name": "apiVersionMajor",
                    "ctype": "uint8_t",
                    "units": "",
                    "desc": "INAV API Major version (`API_VERSION_MAJOR`)."
                },
                {
                    "name": "apiVersionMinor",
                    "ctype": "uint8_t",
                    "units": "",
                    "desc": "INAV API Minor version (`API_VERSION_MINOR`)."
                }
            ],
        },
        "notes": "Used by configurators to check compatibility.",
        "description": "Provides the MSP protocol version and the INAV API version."
    },

Message fields:

name: MSP message name
code: Integer message code
description: String with description of message
request: null or dict of data sent
reply: null or dict of data received
variable_len: Optional boolean, if true, message does not have a predefined fixed length and needs appropriate handling
variants: Optional special case, message has different cases of reply/request. Key/description is not a strict expression or code; just a readable condition
not_implemented: Optional special case, message is not implemented (never or deprecated)
replaced_by: Optional array of MSP message names that replace this command. Present when a command is deprecated and scheduled for removal. Empty array if no replacement is needed
notes: String with details of message

Data dict fields:

payload: Array of payload fields
repeating: Optional Special Case, integer or string of how many times the entire payload is repeated

Payload fields:

Fields:

name: field name from code
ctype: Base C type of the value. Arrays list their element type here as well
desc: Optional string with description and details of field
units: Optional defined units
enum: Optional string of enum struct if value is an enum array: Optional boolean to denote field is array of more values
array_size: If array, integer count of elements. Use 0 when the length is indeterminate/variable
array_size_define: Optional string naming the source #define that provides the size (informational only)
repeating: Optional Special case, contains array of more payload fields that are added Times * Key
payload: If repeating, contains more payload fields
polymorph: Optional boolean special case, field does not have a defined C type and could be anything

Simple value

{
    "name": "mspProtocolVersion",
    "ctype": "uint8_t",
    "units": "",
    "desc": "MSP Protocol version (`MSP_PROTOCOL_VERSION`, typically 0)."
},

Fixed length array

{
    "name": "fcVariantIdentifier",
    "ctype": "char",
    "desc": "4-character identifier string (e.g., \"INAV\"). Defined by `flightControllerIdentifier",
    "array": true,
    "array_size": 4,
    "units": ""
}

Array sized via define

{
    "name": "buildDate",
    "ctype": "char",
    "desc": "Build date string (e.g., \"Dec 31 2023\").",
    "array": true,
    "array_size": 11,
    "array_size_define": "BUILD_DATE_LENGTH",
    "units": ""
}

Undefined length array

{
    "name": "firmwareChunk",
    "ctype": "uint8_t",
    "desc": "Chunk of firmware data",
    "array": true,
    "array_size": 0,
}

As of yet unknown length array

{
    "name": "elementText",
    "ctype": "char",
    "desc": "Static text bytes, not NUL-terminated and not yet sized.",
    "array": true,
    "array_size": 0
}

Nested array with struct

{
    "repeating": "maxVehicles",
    "payload": [
        {
            "name": "adsbVehicle",
            "ctype": "adsbVehicle_t",
            "desc": "Array of `adsbVehicle_t` Repeated `maxVehicles` times",
            "repeating": "maxVehicles",
            "array": true,
            "array_size": 0,
            "units": ""
        }
    ]
}