1 # OpenXC Message Format Specification
3 This specification is a part of the [OpenXC platform][OpenXC].
5 An OpenXC vehicle interface sends generic vehicle data over one or more output
6 interfaces (e.g. USB or Bluetooth) as JSON objects, separated by newlines.
8 There are two valid message types - single valued and evented.
10 There may not be a 1:1 relationship between input and output signals - i.e. raw
11 engine timing CAN signals may be summarized in an "engine performance" metric on
12 the abstract side of the interface.
16 The expected format of a single valued message is:
18 {"name": "steering_wheel_angle", "value": 45}
22 The expected format of an event message is:
24 {"name": "button_event", "value": "up", "event": "pressed"}
26 This format is good for something like a button event, where there are two
27 discrete pieces of information in the measurement.
29 ## Raw CAN Message format
31 An OpenXC vehicle interface may also output raw CAN messages. Each CAN message
32 is sent as a JSON object, separated by newlines. The format of each object is:
34 {"bus": 1, "id": 1234, "value": "0x12345678"}
36 **bus** - the numerical identifier of the CAN bus where this message originated,
37 most likely 1 or 2 (for a vehicle interface with 2 CAN controllers).
39 **id** - the CAN message ID
41 **data** - up to 8 bytes of data from the CAN message's payload, represented as
42 a hexidecimal number in a string. Many JSON parser cannot handle 64-bit
43 integers, which is why we are not using a numerical data type. Each byte in
44 the string *must* be represented with 2 characters, e.g. `0x1` is `0x01` - the
45 complete string must have an even number of characters.
47 ## Diagnostic Messages
51 A request to add or update a diagnostic request is sent to a vehicle interface
52 with this command format:
54 { "command": "diagnostic_request",
61 "multiple_responses": false,
70 **bus** - the numerical identifier of the CAN bus where this request should be
71 sent, most likely 1 or 2 (for a vehicle interface with 2 CAN controllers).
73 **id** - the CAN arbitration ID for the request.
75 **mode** - the OBD-II mode of the request - 1 through 15 (1 through 9 are the
78 **pid** - (optional) the PID for the request, if applicable.
80 **payload** - (optional) up to 7 bytes of data for the request's payload
81 represented as a hexidecimal number in a string. Many JSON parser cannot
82 handle 64-bit integers, which is why we are not using a numerical data type.
83 Each byte in the string *must* be represented with 2 characters, e.g. `0x1`
84 is `0x01` - the complete string must have an even number of characters.
86 **name** - (optional, defaults to nothing) A human readable, string name for
87 this request. If provided, the response will have a `name` field (much like a
88 normal translated message) with this value in place of `bus`, `id`, `mode` and
91 **multiple_responses** - (optional, false by default) if true, request will stay
92 active for a full 100ms, even after receiving a diagnostic response message.
93 This is useful for requests to the functional broadcast arbitration ID
94 (`0x7df`) when you need to get responses from multiple modules. It's possible
95 to set this to `true` for non-broadcast requests, but in practice you won't
96 see any additional responses after the first and it will just take up memory
99 **frequency** - (optional, defaults to 0) The frequency in Hz to send this
100 request. To send a single request, set this to 0 or leave it out.
102 **decoded_type** - (optional, defaults to "obd2" if the request is a recognized
103 OBD-II mode 1 request, otherwise "none") If specified, the valid values are
104 `"none"` and `"obd2"`. If `obd2`, the payload will be decoded according to the
105 OBD-II specification and returned in the `value` field. Set this to `none` to
106 manually override the OBD-II decoding feature for a known PID.
108 The `bus+id+mode+pid` key is unique, so if you send a create request with that
109 key twice, it'll overwrite the existing one (i.e. it will change the frequency,
110 the only other parameter). To cancel a recurring request, send this command with
111 the frequency set to 0.
113 If you're just requesting a PID, you can use this minimal field set for the
116 {"bus": 1, "id": 1234, "mode": 1, "pid": 5}
120 The response to a successful request:
130 and to an unsuccessful request, with the `negative_response_code` and no `pid`
137 "negative_response_code": 17}
139 **bus** - the numerical identifier of the CAN bus where this response was
142 **id** - the CAN arbitration ID for this response.
144 **mode** - the OBD-II mode of the original diagnostic request.
146 **pid** - (optional) the PID for the request, if applicable.
148 **success** - true if the response received was a positive response. If this
149 field is false, the remote node returned an error and the
150 `negative_response_code` field should be populated.
152 **negative_response_code** - (optional) If requested node returned an error,
153 `success` will be `false` and this field will contain the negative response
156 Finally, the `payload` and `value` fields are mutually exclusive:
158 **payload** - (optional) up to 7 bytes of data returned in the response,
159 represented as a hexadecimal number in a string. Many JSON parser cannot
160 handle 64-bit integers, which is why we are not using a numerical data type.
162 **value** - (optional) if the response had a payload, this may be the
163 payload interpreted as an integer.
165 The response to a simple PID request would look like this:
167 {"success": true, "bus": 1, "id": 1234, "mode": 1, "pid": 5, "payload": "0x2"}
173 The `version` command triggers the VI to inject a firmware version identifier
174 response into the outgoing data stream.
178 { "command": "version"}
182 { "command_response": "version", "message": "v6.0-dev (default)"}
186 The `device_id` command triggers the VI to inject a unique device ID (e.g. the
187 MAC address of an included Bluetooth module) into into the outgoing data stream.
191 { "command": "device_id"}
195 { "command_response": "device_id", "message": "0012345678"}
199 An OpenXC vehicle trace file is a plaintext file that contains JSON objects,
200 separated by newlines.
202 The first line may be a metadata object, although this is optional:
207 "vehicle_interface_id": "7ABF",
211 "trim": "V6 Premium",
214 "description": "highway drive to work",
215 "driver_name": "TJ Giuli",
216 "vehicle_id": "17N1039247929"
220 The following lines are OpenXC messages with a `timestamp` field added, e.g.:
222 {"timestamp": 1385133351.285525, "name": "steering_wheel_angle", "value": 45}
224 The timestamp is in [UNIX time](http://en.wikipedia.org/wiki/Unix_time)
225 (i.e. seconds since the UNIX epoch, 00:00:00 UTC, 1/1/1970).
229 These signal names are a part of the OpenXC specification, although some
230 manufacturers may support custom message names.
232 * steering_wheel_angle
233 * numerical, -600 to +600 degrees
235 * torque_at_transmission
236 * numerical, -500 to 1500 Nm
239 * numerical, 0 to 16382 RPM
242 * numerical, 0 to 655 km/h (this will be positive even if going in reverse
243 as it's not a velocity, although you can use the gear status to figure out
246 * accelerator_pedal_position
249 * parking_brake_status
250 * boolean, (true == brake engaged)
251 * 1Hz, but sent immediately on change
253 * boolean (True == pedal pressed)
254 * 1Hz, but sent immediately on change
255 * transmission_gear_position
256 * states: first, second, third, fourth, fifth, sixth, seventh, eighth,
258 * 1Hz, but sent immediately on change
259 * gear_lever_position
260 * states: neutral, park, reverse, drive, sport, low, first, second, third,
262 * 1Hz, but sent immediately on change
265 0 to 16777214.000 km, with about .2m resolution
268 * states: off, accessory, run, start
269 * 1Hz, but sent immediately on change
273 * fuel_consumed_since_restart
274 * numerical, 0 - 4294967295.0 L (this goes to 0 every time the vehicle
275 restarts, like a trip meter)
278 * Value is State: driver, passenger, rear_left, rear_right.
279 * Event is boolean: true == ajar
280 * 1Hz, but sent immediately on change
282 * boolean, true is on
283 * 1Hz, but sent immediately on change
285 * boolean, true is on
286 * 1Hz, but sent immediately on change
287 * windshield_wiper_status
288 * boolean, true is on
289 * 1Hz, but sent immediately on change
291 * numerical, -89.0 to 89.0 degrees with standard GPS accuracy
294 * numerical, -179.0 to 179.0 degrees with standard GPS accuracy
300 Copyright (c) 2012-2013 Ford Motor Company
302 Licensed under the BSD license.
304 [OpenXC]: http://openxcplatform.com