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.
45 ## Diagnostic Messages
54 "parse_payload": true,
59 **bus** - the numerical identifier of the CAN bus where this request should be
60 sent, most likely 1 or 2 (for a vehicle interface with 2 CAN controllers).
62 **id** - the CAN arbitration ID for the request.
64 **mode** - the OBD-II mode of the request - 1 through 15 (1 through 9 are the
67 **pid** - (optional) the PID for the request, if applicable.
69 **payload** - (optional) up to 7 bytes of data for the request's payload
70 represented as a hexidecimal number in a string. Many JSON parser cannot
71 handle 64-bit integers, which is why we are not using a numerical data type.
73 **parse_payload** - (optional, false by default) if true, the complete payload in the
74 response message will be parsed as a number and returned in the 'value' field of
75 the response. The 'payload' field will be omitted in responses with a
78 **factor** - (optional, 1.0 by default) if `parse_payload` is true, the value in
79 the payload will be multiplied by this factor before returning. The `factor`
80 is applied before the `offset`.
82 **offset** - (optional, 0 by default) if `parse_payload` is true, this offset
83 will be added to the value in the payload before returning. The `offset` is
84 applied after the `factor`.
86 **frequency** - (optional, defaults to 0) The frequency in Hz to send this
87 request. To send a single request, set this to 0 or leave it out.
89 TODO it'd be nice to have the OBD-II PIDs built in, with the proper conversion
90 functions - that may need a different output format
92 If you're just requesting a PID, you can use a simplified format for the
95 {"bus": 1, "id": 1234, "mode": 1, "pid": 5}
104 "negative_response_code": 17,
106 "parsed_payload": 4660}
108 **bus** - the numerical identifier of the CAN bus where this response was
111 **id** - the CAN arbitration ID for this response.
113 **mode** - the OBD-II mode of the original diagnostic request.
115 **pid** - (optional) the PID for the request, if applicable.
117 **success** - true if the response received was a positive response. If this
118 field is false, the remote node returned an error and the
119 `negative_response_code` field should be populated.
121 **negative_response_code** - (optional) If requested node returned an error,
122 `success` will be `false` and this field will contain the negative response
125 Finally, the `payload` and `value` fields are mutually exclusive:
127 **payload** - (optional) up to 7 bytes of data returned in the response,
128 represented as a hexadecimal number in a string. Many JSON parser cannot
129 handle 64-bit integers, which is why we are not using a numerical data type.
131 **value** - (optional) if the response had a payload, this may be the
132 payload interpreted as an integer and transformed with a factor and offset
133 provided with the request.
135 The response to a simple PID request would look like this:
137 {"bus": 1, "id": 1234, "mode": 1, "pid": 5, "payload": "0x2"}
139 TODO again, it'd be nice to have the OBD-II PIDs built in, with the proper
140 conversion functions so the response here included the actual transformed value
141 of the pid and a human readable name
145 An OpenXC vehicle trace file is a plaintext file that contains JSON objects,
146 separated by newlines.
148 The first line may be a metadata object, although this is optional:
153 "vehicle_interface_id": "7ABF",
157 "trim": "V6 Premium",
160 "description": "highway drive to work",
161 "driver_name": "TJ Giuli",
162 "vehicle_id": "17N1039247929"
166 The following lines are OpenXC messages with a `timestamp` field added, e.g.:
168 {"timestamp": 1385133351.285525, "name": "steering_wheel_angle", "value": 45}
170 The timestamp is in [UNIX time](http://en.wikipedia.org/wiki/Unix_time)
171 (i.e. seconds since the UNIX epoch, 00:00:00 UTC, 1/1/1970).
175 These signal names are a part of the OpenXC specification, although some
176 manufacturers may support custom message names.
178 * steering_wheel_angle
179 * numerical, -600 to +600 degrees
181 * torque_at_transmission
182 * numerical, -500 to 1500 Nm
185 * numerical, 0 to 16382 RPM
188 * numerical, 0 to 655 km/h (this will be positive even if going in reverse
189 as it's not a velocity, although you can use the gear status to figure out
192 * accelerator_pedal_position
195 * parking_brake_status
196 * boolean, (true == brake engaged)
197 * 1Hz, but sent immediately on change
199 * boolean (True == pedal pressed)
200 * 1Hz, but sent immediately on change
201 * transmission_gear_position
202 * states: first, second, third, fourth, fifth, sixth, seventh, eighth,
204 * 1Hz, but sent immediately on change
205 * gear_lever_position
206 * states: neutral, park, reverse, drive, sport, low, first, second, third,
208 * 1Hz, but sent immediately on change
211 0 to 16777214.000 km, with about .2m resolution
214 * states: off, accessory, run, start
215 * 1Hz, but sent immediately on change
219 * fuel_consumed_since_restart
220 * numerical, 0 - 4294967295.0 L (this goes to 0 every time the vehicle
221 restarts, like a trip meter)
224 * Value is State: driver, passenger, rear_left, rear_right.
225 * Event is boolean: true == ajar
226 * 1Hz, but sent immediately on change
228 * boolean, true is on
229 * 1Hz, but sent immediately on change
231 * boolean, true is on
232 * 1Hz, but sent immediately on change
233 * windshield_wiper_status
234 * boolean, true is on
235 * 1Hz, but sent immediately on change
237 * numerical, -89.0 to 89.0 degrees with standard GPS accuracy
240 * numerical, -179.0 to 179.0 degrees with standard GPS accuracy
246 Copyright (c) 2012-2013 Ford Motor Company
248 Licensed under the BSD license.
250 [OpenXC]: http://openxcplatform.com