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_response": 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_response** - (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 TODO it'd be nice to have the OBD-II PIDs built in, with the proper conversion
122 functions - that may need a different output format
124 If you're just requesting a PID, you can use this minimal field set for the
127 {"bus": 1, "id": 1234, "mode": 1, "pid": 5}
136 "negative_response_code": 17,
138 "parsed_payload": 4660}
140 **bus** - the numerical identifier of the CAN bus where this response was
143 **id** - the CAN arbitration ID for this response.
145 **mode** - the OBD-II mode of the original diagnostic request.
147 **pid** - (optional) the PID for the request, if applicable.
149 **success** - true if the response received was a positive response. If this
150 field is false, the remote node returned an error and the
151 `negative_response_code` field should be populated.
153 **negative_response_code** - (optional) If requested node returned an error,
154 `success` will be `false` and this field will contain the negative response
157 Finally, the `payload` and `value` fields are mutually exclusive:
159 **payload** - (optional) up to 7 bytes of data returned in the response,
160 represented as a hexadecimal number in a string. Many JSON parser cannot
161 handle 64-bit integers, which is why we are not using a numerical data type.
163 **value** - (optional) if the response had a payload, this may be the
164 payload interpreted as an integer and transformed with a factor and offset
165 provided with the request.
167 The response to a simple PID request would look like this:
169 {"bus": 1, "id": 1234, "mode": 1, "pid": 5, "payload": "0x2"}
171 TODO again, it'd be nice to have the OBD-II PIDs built in, with the proper
172 conversion functions so the response here included the actual transformed value
173 of the pid and a human readable name
177 An OpenXC vehicle trace file is a plaintext file that contains JSON objects,
178 separated by newlines.
180 The first line may be a metadata object, although this is optional:
185 "vehicle_interface_id": "7ABF",
189 "trim": "V6 Premium",
192 "description": "highway drive to work",
193 "driver_name": "TJ Giuli",
194 "vehicle_id": "17N1039247929"
198 The following lines are OpenXC messages with a `timestamp` field added, e.g.:
200 {"timestamp": 1385133351.285525, "name": "steering_wheel_angle", "value": 45}
202 The timestamp is in [UNIX time](http://en.wikipedia.org/wiki/Unix_time)
203 (i.e. seconds since the UNIX epoch, 00:00:00 UTC, 1/1/1970).
207 These signal names are a part of the OpenXC specification, although some
208 manufacturers may support custom message names.
210 * steering_wheel_angle
211 * numerical, -600 to +600 degrees
213 * torque_at_transmission
214 * numerical, -500 to 1500 Nm
217 * numerical, 0 to 16382 RPM
220 * numerical, 0 to 655 km/h (this will be positive even if going in reverse
221 as it's not a velocity, although you can use the gear status to figure out
224 * accelerator_pedal_position
227 * parking_brake_status
228 * boolean, (true == brake engaged)
229 * 1Hz, but sent immediately on change
231 * boolean (True == pedal pressed)
232 * 1Hz, but sent immediately on change
233 * transmission_gear_position
234 * states: first, second, third, fourth, fifth, sixth, seventh, eighth,
236 * 1Hz, but sent immediately on change
237 * gear_lever_position
238 * states: neutral, park, reverse, drive, sport, low, first, second, third,
240 * 1Hz, but sent immediately on change
243 0 to 16777214.000 km, with about .2m resolution
246 * states: off, accessory, run, start
247 * 1Hz, but sent immediately on change
251 * fuel_consumed_since_restart
252 * numerical, 0 - 4294967295.0 L (this goes to 0 every time the vehicle
253 restarts, like a trip meter)
256 * Value is State: driver, passenger, rear_left, rear_right.
257 * Event is boolean: true == ajar
258 * 1Hz, but sent immediately on change
260 * boolean, true is on
261 * 1Hz, but sent immediately on change
263 * boolean, true is on
264 * 1Hz, but sent immediately on change
265 * windshield_wiper_status
266 * boolean, true is on
267 * 1Hz, but sent immediately on change
269 * numerical, -89.0 to 89.0 degrees with standard GPS accuracy
272 * numerical, -179.0 to 179.0 degrees with standard GPS accuracy
278 Copyright (c) 2012-2013 Ford Motor Company
280 Licensed under the BSD license.
282 [OpenXC]: http://openxcplatform.com