# 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.
The `bus+id+mode+pid` key is unique, so if you send a create request with that
key twice, it'll overwrite the existing one (i.e. it will change the frequency,
the only other parameter). To cancel a recurring request, send this command with
the frequency set to 0.
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