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 "parse_payload": true,
62 "multiple_responses": false,
71 **bus** - the numerical identifier of the CAN bus where this request should be
72 sent, most likely 1 or 2 (for a vehicle interface with 2 CAN controllers).
74 **id** - the CAN arbitration ID for the request.
76 **mode** - the OBD-II mode of the request - 1 through 15 (1 through 9 are the
79 **pid** - (optional) the PID for the request, if applicable.
81 **payload** - (optional) up to 7 bytes of data for the request's payload
82 represented as a hexidecimal number in a string. Many JSON parser cannot
83 handle 64-bit integers, which is why we are not using a numerical data type.
84 Each byte in the string *must* be represented with 2 characters, e.g. `0x1`
85 is `0x01` - the complete string must have an even number of characters.
87 **parse_payload** - (optional, false by default) if true, the complete payload in the
88 response message will be parsed as a number and returned in the 'value' field of
89 the response. The 'payload' field will be omitted in responses with a
92 **multiple_responses** - (optional, false by default) if true, request will stay
93 active for a full 100ms, even after receiving a diagnostic response message.
94 This is useful for requests to the functional broadcast arbitration ID
95 (`0x7df`) when you need to get responses from multiple modules. It's possible
96 to set this to `true` for non-broadcast requests, but in practice you won't
97 see any additional responses after the first and it will just take up memory
100 **factor** - (optional, 1.0 by default) if `parse_payload` is true, the value in
101 the payload will be multiplied by this factor before returning. The `factor`
102 is applied before the `offset`.
104 **offset** - (optional, 0 by default) if `parse_payload` is true, this offset
105 will be added to the value in the payload before returning. The `offset` is
106 applied after the `factor`.
108 **frequency** - (optional, defaults to 0) The frequency in Hz to send this
109 request. To send a single request, set this to 0 or leave it out.
111 **name** - (optional, defaults to nothing) A human readable, string name for
112 this request. If provided, the response will have a `name` field (much like a
113 normal translated message) in place of the request details (i.e. the bus,
114 id, mode and pid). TODO elaborate on this.
116 The `bus+id+mode+pid` key is unique, so if you send a create request with that
117 key twice, it'll overwrite the existing one (i.e. it will change the frequency,
118 the only other parameter). To cancel a recurring request, send this command with
119 the frequency set to 0.
121 If you're just requesting a PID, you can use this minimal field set for the
124 {"bus": 1, "id": 1234, "mode": 1, "pid": 5}
128 The response to a successful request:
138 and to an unsuccessful request, with the `negative_response_code` and no `pid`
145 "negative_response_code": 17}
147 **bus** - the numerical identifier of the CAN bus where this response was
150 **id** - the CAN arbitration ID for this response.
152 **mode** - the OBD-II mode of the original diagnostic request.
154 **pid** - (optional) the PID for the request, if applicable.
156 **success** - true if the response received was a positive response. If this
157 field is false, the remote node returned an error and the
158 `negative_response_code` field should be populated.
160 **negative_response_code** - (optional) If requested node returned an error,
161 `success` will be `false` and this field will contain the negative response
164 Finally, the `payload` and `value` fields are mutually exclusive:
166 **payload** - (optional) up to 7 bytes of data returned in the response,
167 represented as a hexadecimal number in a string. Many JSON parser cannot
168 handle 64-bit integers, which is why we are not using a numerical data type.
170 **value** - (optional) if the response had a payload, this may be the
171 payload interpreted as an integer and transformed with a factor and offset
172 provided with the request.
174 The response to a simple PID request would look like this:
176 {"success": true, "bus": 1, "id": 1234, "mode": 1, "pid": 5, "payload": "0x2"}
182 The `version` command triggers the VI to inject a firmware version identifier
183 response into the outgoing data stream.
187 { "command": "version"}
191 { "command_response": "version", "message": "v6.0-dev (default)"}
195 The `device_id` command triggers the VI to inject a unique device ID (e.g. the
196 MAC address of an included Bluetooth module) into into the outgoing data stream.
200 { "command": "device_id"}
204 { "command_response": "device_id", "message": "0012345678"}
208 An OpenXC vehicle trace file is a plaintext file that contains JSON objects,
209 separated by newlines.
211 The first line may be a metadata object, although this is optional:
216 "vehicle_interface_id": "7ABF",
220 "trim": "V6 Premium",
223 "description": "highway drive to work",
224 "driver_name": "TJ Giuli",
225 "vehicle_id": "17N1039247929"
229 The following lines are OpenXC messages with a `timestamp` field added, e.g.:
231 {"timestamp": 1385133351.285525, "name": "steering_wheel_angle", "value": 45}
233 The timestamp is in [UNIX time](http://en.wikipedia.org/wiki/Unix_time)
234 (i.e. seconds since the UNIX epoch, 00:00:00 UTC, 1/1/1970).
238 These signal names are a part of the OpenXC specification, although some
239 manufacturers may support custom message names.
241 * steering_wheel_angle
242 * numerical, -600 to +600 degrees
244 * torque_at_transmission
245 * numerical, -500 to 1500 Nm
248 * numerical, 0 to 16382 RPM
251 * numerical, 0 to 655 km/h (this will be positive even if going in reverse
252 as it's not a velocity, although you can use the gear status to figure out
255 * accelerator_pedal_position
258 * parking_brake_status
259 * boolean, (true == brake engaged)
260 * 1Hz, but sent immediately on change
262 * boolean (True == pedal pressed)
263 * 1Hz, but sent immediately on change
264 * transmission_gear_position
265 * states: first, second, third, fourth, fifth, sixth, seventh, eighth,
267 * 1Hz, but sent immediately on change
268 * gear_lever_position
269 * states: neutral, park, reverse, drive, sport, low, first, second, third,
271 * 1Hz, but sent immediately on change
274 0 to 16777214.000 km, with about .2m resolution
277 * states: off, accessory, run, start
278 * 1Hz, but sent immediately on change
282 * fuel_consumed_since_restart
283 * numerical, 0 - 4294967295.0 L (this goes to 0 every time the vehicle
284 restarts, like a trip meter)
287 * Value is State: driver, passenger, rear_left, rear_right.
288 * Event is boolean: true == ajar
289 * 1Hz, but sent immediately on change
291 * boolean, true is on
292 * 1Hz, but sent immediately on change
294 * boolean, true is on
295 * 1Hz, but sent immediately on change
296 * windshield_wiper_status
297 * boolean, true is on
298 * 1Hz, but sent immediately on change
300 * numerical, -89.0 to 89.0 degrees with standard GPS accuracy
303 * numerical, -179.0 to 179.0 degrees with standard GPS accuracy
309 Copyright (c) 2012-2013 Ford Motor Company
311 Licensed under the BSD license.
313 [OpenXC]: http://openxcplatform.com