1 # OpenXC Message Format Specification
5 This specification is a part of the [OpenXC platform][OpenXC].
7 An OpenXC vehicle interface sends generic vehicle data over one or more output
8 interfaces (e.g. USB or Bluetooth) as JSON or Protocol Buffers (protobuf).
10 This document describes the JSON format and includes a high level description of
11 each type and field. Each JSON message published by a VI is delimited with a
14 The Protocol Buffer format is specified in the file `openxc.proto`. Those are
15 published using the standard length-delimited method (any protobuf library
20 There may not be a 1:1 relationship between input and output signals - i.e. raw
21 engine timing CAN signals may be summarized in an "engine performance" metric on
22 the abstract side of the interface.
24 The expected format of a single valued message is:
26 {"name": "steering_wheel_angle", "value": 45}
30 The expected format of an event message is:
32 {"name": "button_event", "value": "up", "event": "pressed"}
34 This format is good for something like a button event, where there are two
35 discrete pieces of information in the measurement.
37 ## Raw CAN Message format
39 The format for a raw CAN message:
41 {"bus": 1, "id": 1234, "value": "0x12345678"}
43 **bus** - the numerical identifier of the CAN bus where this message originated,
44 most likely 1 or 2 (for a vehicle interface with 2 CAN controllers).
46 **id** - the CAN message ID
48 **data** - up to 8 bytes of data from the CAN message's payload, represented as
49 a hexidecimal number in a string. Many JSON parser cannot handle 64-bit
50 integers, which is why we are not using a numerical data type. Each byte in
51 the string *must* be represented with 2 characters, e.g. `0x1` is `0x01` - the
52 complete string must have an even number of characters.
54 ## Diagnostic Messages
58 A request to add or update a diagnostic request is sent to a vehicle interface
59 with this command format:
61 { "command": "diagnostic_request",
68 "multiple_responses": false,
77 **bus** - the numerical identifier of the CAN bus where this request should be
78 sent, most likely 1 or 2 (for a vehicle interface with 2 CAN controllers).
80 **id** - the CAN arbitration ID for the request.
82 **mode** - the OBD-II mode of the request - 1 through 15 (1 through 9 are the
85 **pid** - (optional) the PID for the request, if applicable.
87 **payload** - (optional) up to 7 bytes of data for the request's payload
88 represented as a hexidecimal number in a string. Many JSON parser cannot
89 handle 64-bit integers, which is why we are not using a numerical data type.
90 Each byte in the string *must* be represented with 2 characters, e.g. `0x1`
91 is `0x01` - the complete string must have an even number of characters.
93 **name** - (optional, defaults to nothing) A human readable, string name for
94 this request. If provided, the response will have a `name` field (much like a
95 normal translated message) with this value in place of `bus`, `id`, `mode` and
98 **multiple_responses** - (optional, false by default) if true, request will stay
99 active for a full 100ms, even after receiving a diagnostic response message.
100 This is useful for requests to the functional broadcast arbitration ID
101 (`0x7df`) when you need to get responses from multiple modules. It's possible
102 to set this to `true` for non-broadcast requests, but in practice you won't
103 see any additional responses after the first and it will just take up memory
104 in the VI for longer.
106 **frequency** - (optional, defaults to 0) The frequency in Hz to send this
107 request. To send a single non-recurring request, set this to 0 or leave it
110 **decoded_type** - (optional, defaults to "obd2" if the request is a recognized
111 OBD-II mode 1 request, otherwise "none") If specified, the valid values are
112 `"none"` and `"obd2"`. If `obd2`, the payload will be decoded according to the
113 OBD-II specification and returned in the `value` field. Set this to `none` to
114 manually override the OBD-II decoding feature for a known PID.
116 A diagnostic request's `bus`, `id`, `mode` and `pid` (or lack of a `pid`)
117 combine to create a unique key to identify a recurring request. This means that
118 you cannot simultaneosly have recurring requests at 2Hz and 5Hz for the same PID
121 If you send a new `diagnostic_request` command with a `bus + id + mode + pid`
122 key matching an existing recurring request, it will update it with whatever
123 other parameters you've provided (e.g. it will change the frequency if you
126 To cancel a recurring request, send a `diagnostic_request` command with the
127 matching request information (i.e. the `bus`, `id`, `mode` and `pid`) but a
130 Non-recurring requests may have the same `bus+id+mode(+pid)` key as a recurring
131 request, and they will co-exist without issue. As soon as a non-recurring
132 request is either completed or times out, it is removed from the active list.
134 If you're just requesting a PID, you can use this minimal field set for the
137 {"bus": 1, "id": 1234, "mode": 1, "pid": 5}
141 The response to a successful request:
151 and to an unsuccessful request, with the `negative_response_code` and no `pid`
158 "negative_response_code": 17}
160 **bus** - the numerical identifier of the CAN bus where this response was
163 **id** - the CAN arbitration ID for this response.
165 **mode** - the OBD-II mode of the original diagnostic request.
167 **pid** - (optional) the PID for the request, if applicable.
169 **success** - true if the response received was a positive response. If this
170 field is false, the remote node returned an error and the
171 `negative_response_code` field should be populated.
173 **negative_response_code** - (optional) If requested node returned an error,
174 `success` will be `false` and this field will contain the negative response
177 Finally, the `payload` and `value` fields are mutually exclusive:
179 **payload** - (optional) up to 7 bytes of data returned in the response,
180 represented as a hexadecimal number in a string. Many JSON parser cannot
181 handle 64-bit integers, which is why we are not using a numerical data type.
183 **value** - (optional) if the response had a payload, this may be the
184 payload interpreted as an integer.
186 The response to a simple PID request would look like this:
188 {"success": true, "bus": 1, "id": 1234, "mode": 1, "pid": 5, "payload": "0x2"}
194 The `version` command triggers the VI to inject a firmware version identifier
195 response into the outgoing data stream.
199 { "command": "version"}
203 { "command_response": "version", "message": "v6.0-dev (default)"}
207 The `device_id` command triggers the VI to inject a unique device ID (e.g. the
208 MAC address of an included Bluetooth module) into into the outgoing data stream.
212 { "command": "device_id"}
216 { "command_response": "device_id", "message": "0012345678"}
220 An OpenXC vehicle trace file is a plaintext file that contains JSON objects,
221 separated by newlines (which may be either `\r\n` or `\n`, depending on the
222 platform the trace file was recorded).
224 The first line may be a metadata object, although this is optional:
229 "vehicle_interface_id": "7ABF",
233 "trim": "V6 Premium",
236 "description": "highway drive to work",
237 "driver_name": "TJ Giuli",
238 "vehicle_id": "17N1039247929"
242 The following lines are OpenXC messages with a `timestamp` field added, e.g.:
244 {"timestamp": 1385133351.285525, "name": "steering_wheel_angle", "value": 45}
246 The timestamp is in [UNIX time](http://en.wikipedia.org/wiki/Unix_time)
247 (i.e. seconds since the UNIX epoch, 00:00:00 UTC, 1/1/1970).
251 These signal names are a part of the OpenXC specification, although some
252 manufacturers may support custom message names.
254 * steering_wheel_angle
255 * numerical, -600 to +600 degrees
257 * torque_at_transmission
258 * numerical, -500 to 1500 Nm
261 * numerical, 0 to 16382 RPM
264 * numerical, 0 to 655 km/h (this will be positive even if going in reverse
265 as it's not a velocity, although you can use the gear status to figure out
268 * accelerator_pedal_position
271 * parking_brake_status
272 * boolean, (true == brake engaged)
273 * 1Hz, but sent immediately on change
275 * boolean (True == pedal pressed)
276 * 1Hz, but sent immediately on change
277 * transmission_gear_position
278 * states: first, second, third, fourth, fifth, sixth, seventh, eighth,
279 ninth, tenth, reverse, neutral
280 * 1Hz, but sent immediately on change
281 * gear_lever_position
282 * states: neutral, park, reverse, drive, sport, low, first, second, third,
283 fourth, fifth, sixth, seventh, eighth, ninth, tenth
284 * 1Hz, but sent immediately on change
287 0 to 16777214.000 km, with about .2m resolution
290 * states: off, accessory, run, start
291 * 1Hz, but sent immediately on change
295 * fuel_consumed_since_restart
296 * numerical, 0 - 4294967295.0 L (this goes to 0 every time the vehicle
297 restarts, like a trip meter)
300 * Value is State: driver, passenger, rear_left, rear_right.
301 * Event is boolean: true == ajar
302 * 1Hz, but sent immediately on change
304 * boolean, true is on
305 * 1Hz, but sent immediately on change
307 * boolean, true is on
308 * 1Hz, but sent immediately on change
309 * windshield_wiper_status
310 * boolean, true is on
311 * 1Hz, but sent immediately on change
313 * numerical, -89.0 to 89.0 degrees with standard GPS accuracy
316 * numerical, -179.0 to 179.0 degrees with standard GPS accuracy
319 ### Signals from Diagnostics Messages
321 This set of signals is often retreived from OBD-II requests. The units can be
322 found in the [OBD-II standard](http://en.wikipedia.org/wiki/OBD-II_PIDs#Mode_01).
325 * engine_coolant_temperature
326 * barometric_pressure
327 * commanded_throttle_position
330 * intake_air_temperature
331 * intake_manifold_pressure
335 * accelerator_pedal_position
336 * ethanol_fuel_percentage
337 * engine_oil_temperature
343 Copyright (c) 2012-2014 Ford Motor Company
345 Licensed under the BSD license.
347 [OpenXC]: http://openxcplatform.com