# OpenXC Message Format Specification
-Version: v0.3
+Version: v0.4-dev
This specification is a part of the [OpenXC platform][OpenXC].
An OpenXC vehicle interface sends generic vehicle data over one or more output
interfaces (e.g. USB or Bluetooth) as JSON or Protocol Buffers (protobuf).
-This document describes the JSON format and includes a high level description of
-each type and field. Each JSON message published by a VI is delimited with a
-`\0` character.
+## Binary (Protocol Buffers)
The Protocol Buffer format is specified in the file `openxc.proto`. Those are
published using the standard length-delimited method (any protobuf library
should support this).
-## Single Valued
+## JSON
+
+This document describes the JSON format and includes a high level description of
+each type and field. Each JSON message published by a VI is delimited with a
+`\0 ` character.
+
+### Extra Values
+
+Any of the following JSON objects may optionally include an `extras`
+field. The value may be any valid JSON object or array. The client libraries
+will do their best to parse this information into a generic format and pass it
+to your application. For example:
+
+ {"name": "steering_wheel_angle", "value": 45,
+ "extras": {
+ "calibrated": false
+ }
+ }
+
+### Single Valued
There may not be a 1:1 relationship between input and output signals - i.e. raw
engine timing CAN signals may be summarized in an "engine performance" metric on
{"name": "steering_wheel_angle", "value": 45}
-## Evented
+### Evented
The expected format of an event message is:
This format is good for something like a button event, where there are two
discrete pieces of information in the measurement.
-## Raw CAN Message format
+### Raw CAN Message format
The format for a raw CAN message:
the string *must* be represented with 2 characters, e.g. `0x1` is `0x01` - the
complete string must have an even number of characters.
-## Diagnostic Messages
+### Diagnostic Messages
-### Requests
+#### Requests
A request to add or update a diagnostic request is sent to a vehicle interface
with this command format:
"pid": 5,
"payload": "0x1234",
"multiple_responses": false,
- "factor": 1.0,
- "offset": 0,
"frequency": 1,
"name": "my_pid"
}
**id** - the CAN arbitration ID for the request.
-**mode** - the OBD-II mode of the request - 1 through 15 (1 through 9 are the
- standardized modes).
+**mode** - the OBD-II mode of the request - 1 through 255 (1 through 9 are the
+ standardized modes and 0x22 is a common proprietary mode).
**pid** - (optional) the PID for the request, if applicable.
{"bus": 1, "id": 1234, "mode": 1, "pid": 5}
-### Responses
+#### Responses
The response to a successful request:
{"success": true, "bus": 1, "id": 1234, "mode": 1, "pid": 5, "payload": "0x2"}
-## Commands
+### Commands
-### Version Query
+#### Version Query
The `version` command triggers the VI to inject a firmware version identifier
response into the outgoing data stream.
{ "command_response": "version", "message": "v6.0-dev (default)"}
-### Device ID Query
+#### Device ID Query
The `device_id` command triggers the VI to inject a unique device ID (e.g. the
MAC address of an included Bluetooth module) into into the outgoing data stream.
{ "command_response": "device_id", "message": "0012345678"}
-## Trace File Format
+### Trace File Format
An OpenXC vehicle trace file is a plaintext file that contains JSON objects,
separated by newlines (which may be either `\r\n` or `\n`, depending on the