# OpenXC Message Format Specification 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 objects, separated by newlines. There are two valid message types - single valued and evented. 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 the abstract side of the interface. ## Single Valued The expected format of a single valued message is: {"name": "steering_wheel_angle", "value": 45} ## Evented The expected format of an event message is: {"name": "button_event", "value": "up", "event": "pressed"} 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 An OpenXC vehicle interface may also output raw CAN messages. Each CAN message is sent as a JSON object, separated by newlines. The format of each object is: {"bus": 1, "id": 1234, "value": "0x12345678"} **bus** - the numerical identifier of the CAN bus where this message originated, most likely 1 or 2 (for a vehicle interface with 2 CAN controllers). **id** - the CAN message ID **data** - up to 8 bytes of data from the CAN message's payload, represented as a hexidecimal number in a string. Many JSON parser cannot handle 64-bit integers, which is why we are not using a numerical data type. ## Diagnostic Messages ### Requests A request to add or update a diagnostic request is sent to a vehicle interface with this command format: { "command": "diagnostic_request", "request": { "bus": 1, "id": 1234, "mode": 1, "pid": 5, "payload": "0x1234", "parse_payload": true, "factor": 1.0, "offset": 0, "frequency": 1 } } } **bus** - the numerical identifier of the CAN bus where this request should be sent, most likely 1 or 2 (for a vehicle interface with 2 CAN controllers). **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). **pid** - (optional) the PID for the request, if applicable. **payload** - (optional) up to 7 bytes of data for the request's payload represented as a hexidecimal number in a string. Many JSON parser cannot handle 64-bit integers, which is why we are not using a numerical data type. **parse_payload** - (optional, false by default) if true, the complete payload in the response message will be parsed as a number and returned in the 'value' field of the response. The 'payload' field will be omitted in responses with a 'value'. **factor** - (optional, 1.0 by default) if `parse_payload` is true, the value in the payload will be multiplied by this factor before returning. The `factor` is applied before the `offset`. **offset** - (optional, 0 by default) if `parse_payload` is true, this offset will be added to the value in the payload before returning. The `offset` is applied after the `factor`. **frequency** - (optional, defaults to 0) The frequency in Hz to send this request. To send a single request, set this to 0 or leave it out. TODO it'd be nice to have the OBD-II PIDs built in, with the proper conversion functions - that may need a different output format If you're just requesting a PID, you can use this minimal field set for the `request` object: {"bus": 1, "id": 1234, "mode": 1, "pid": 5} ### Responses {"bus": 1, "id": 1234, "mode": 1, "pid": 5, "success": true, "negative_response_code": 17, "payload": "0x1234", "parsed_payload": 4660} **bus** - the numerical identifier of the CAN bus where this response was received. **id** - the CAN arbitration ID for this response. **mode** - the OBD-II mode of the original diagnostic request. **pid** - (optional) the PID for the request, if applicable. **success** - true if the response received was a positive response. If this field is false, the remote node returned an error and the `negative_response_code` field should be populated. **negative_response_code** - (optional) If requested node returned an error, `success` will be `false` and this field will contain the negative response code (NRC). Finally, the `payload` and `value` fields are mutually exclusive: **payload** - (optional) up to 7 bytes of data returned in the response, represented as a hexadecimal number in a string. Many JSON parser cannot handle 64-bit integers, which is why we are not using a numerical data type. **value** - (optional) if the response had a payload, this may be the payload interpreted as an integer and transformed with a factor and offset provided with the request. The response to a simple PID request would look like this: {"bus": 1, "id": 1234, "mode": 1, "pid": 5, "payload": "0x2"} TODO again, it'd be nice to have the OBD-II PIDs built in, with the proper conversion functions so the response here included the actual transformed value of the pid and a human readable name ## Trace File Format An OpenXC vehicle trace file is a plaintext file that contains JSON objects, separated by newlines. The first line may be a metadata object, although this is optional: ``` {"metadata": { "version": "v3.0", "vehicle_interface_id": "7ABF", "vehicle": { "make": "Ford", "model": "Mustang", "trim": "V6 Premium", "year": 2013 }, "description": "highway drive to work", "driver_name": "TJ Giuli", "vehicle_id": "17N1039247929" } ``` The following lines are OpenXC messages with a `timestamp` field added, e.g.: {"timestamp": 1385133351.285525, "name": "steering_wheel_angle", "value": 45} The timestamp is in [UNIX time](http://en.wikipedia.org/wiki/Unix_time) (i.e. seconds since the UNIX epoch, 00:00:00 UTC, 1/1/1970). ## Official Signals These signal names are a part of the OpenXC specification, although some manufacturers may support custom message names. * steering_wheel_angle * numerical, -600 to +600 degrees * 10Hz * torque_at_transmission * numerical, -500 to 1500 Nm * 10Hz * engine_speed * numerical, 0 to 16382 RPM * 10Hz * vehicle_speed * numerical, 0 to 655 km/h (this will be positive even if going in reverse as it's not a velocity, although you can use the gear status to figure out direction) * 10Hz * accelerator_pedal_position * percentage * 10Hz * parking_brake_status * boolean, (true == brake engaged) * 1Hz, but sent immediately on change * brake_pedal_status * boolean (True == pedal pressed) * 1Hz, but sent immediately on change * transmission_gear_position * states: first, second, third, fourth, fifth, sixth, seventh, eighth, reverse, neutral * 1Hz, but sent immediately on change * gear_lever_position * states: neutral, park, reverse, drive, sport, low, first, second, third, fourth, fifth, sixth * 1Hz, but sent immediately on change * odometer * Numerical, km 0 to 16777214.000 km, with about .2m resolution * 10Hz * ignition_status * states: off, accessory, run, start * 1Hz, but sent immediately on change * fuel_level * percentage * 2Hz * fuel_consumed_since_restart * numerical, 0 - 4294967295.0 L (this goes to 0 every time the vehicle restarts, like a trip meter) * 10Hz * door_status * Value is State: driver, passenger, rear_left, rear_right. * Event is boolean: true == ajar * 1Hz, but sent immediately on change * headlamp_status * boolean, true is on * 1Hz, but sent immediately on change * high_beam_status * boolean, true is on * 1Hz, but sent immediately on change * windshield_wiper_status * boolean, true is on * 1Hz, but sent immediately on change * latitude * numerical, -89.0 to 89.0 degrees with standard GPS accuracy * 1Hz * longitude * numerical, -179.0 to 179.0 degrees with standard GPS accuracy * 1Hz License ======= Copyright (c) 2012-2013 Ford Motor Company Licensed under the BSD license. [OpenXC]: http://openxcplatform.com