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
56 **bus** - the numerical identifier of the CAN bus where this request should be
57 sent, most likely 1 or 2 (for a vehicle interface with 2 CAN controllers).
59 **id** - the CAN arbitration ID for the request.
61 **mode** - the OBD-II mode of the request - 0x1 through 0xf (0x1 through 0xa
62 are the standardized modes).
64 **pid** - (optional) the PID for the request, if applicable.
66 **payload** - (optional) up to 7 bytes of data for the request's payload
67 represented as a hexidecimal number in a string. Many JSON parser cannot
68 handle 64-bit integers, which is why we are not using a numerical data type.
70 **frequency** - (optional, defaults to 0) The frequency in Hz to send this
71 request. To send a single request, set this to 0 or leave it out.
73 TODO it'd be nice to have the OBD-II PIDs built in, with the proper conversion
74 functions - that may need a different output format
76 If you're just requesting a PID, you can use a simplified format for the
79 {"bus": 1, "id": 1234, "mode": 1, "pid": 5}
88 "negative_response_code": 17,
91 **bus** - the numerical identifier of the CAN bus where this response was
94 **id** - the CAN arbitration ID for this response.
96 **mode** - the OBD-II mode of the original diagnostic request.
98 **pid** - (optional) the PID for the request, if applicable.
100 **success** - true if the response received was a positive response. If this
101 field is false, the remote node returned an error and the
102 `negative_response_code` field should be populated.
104 **negative_response_code** - (optional) If requsted node returned an error,
105 `success` will be `false` and this field will contain the negative response
108 **payload** - (optional) up to 7 bytes of data returned in the response,
109 represented as a hexidecimal number in a string. Many JSON parser cannot
110 handle 64-bit integers, which is why we are not using a numerical data type.
112 The response to a simple PID requset would look like this:
114 {"bus": 1, "id": 1234, "mode": 1, "pid": 5, "payload": "0x2"}
116 TODO again, it'd be nice to have the OBD-II PIDs built in, with the proper
117 conversion functions so the response here included the actual transformed value
118 of the pid and a human readable name
122 An OpenXC vehicle trace file is a plaintext file that contains JSON objects,
123 separated by newlines.
125 The first line may be a metadata object, although this is optional:
130 "vehicle_interface_id": "7ABF",
134 "trim": "V6 Premium",
137 "description": "highway drive to work",
138 "driver_name": "TJ Giuli",
139 "vehicle_id": "17N1039247929"
143 The following lines are OpenXC messages with a `timestamp` field added, e.g.:
145 {"timestamp": 1385133351.285525, "name": "steering_wheel_angle", "value": 45}
147 The timestamp is in [UNIX time](http://en.wikipedia.org/wiki/Unix_time)
148 (i.e. seconds since the UNIX epoch, 00:00:00 UTC, 1/1/1970).
152 These signal names are a part of the OpenXC specification, although some
153 manufacturers may support custom message names.
155 * steering_wheel_angle
156 * numerical, -600 to +600 degrees
158 * torque_at_transmission
159 * numerical, -500 to 1500 Nm
162 * numerical, 0 to 16382 RPM
165 * numerical, 0 to 655 km/h (this will be positive even if going in reverse
166 as it's not a velocity, although you can use the gear status to figure out
169 * accelerator_pedal_position
172 * parking_brake_status
173 * boolean, (true == brake engaged)
174 * 1Hz, but sent immediately on change
176 * boolean (True == pedal pressed)
177 * 1Hz, but sent immediately on change
178 * transmission_gear_position
179 * states: first, second, third, fourth, fifth, sixth, seventh, eighth,
181 * 1Hz, but sent immediately on change
182 * gear_lever_position
183 * states: neutral, park, reverse, drive, sport, low, first, second, third,
185 * 1Hz, but sent immediately on change
188 0 to 16777214.000 km, with about .2m resolution
191 * states: off, accessory, run, start
192 * 1Hz, but sent immediately on change
196 * fuel_consumed_since_restart
197 * numerical, 0 - 4294967295.0 L (this goes to 0 every time the vehicle
198 restarts, like a trip meter)
201 * Value is State: driver, passenger, rear_left, rear_right.
202 * Event is boolean: true == ajar
203 * 1Hz, but sent immediately on change
205 * boolean, true is on
206 * 1Hz, but sent immediately on change
208 * boolean, true is on
209 * 1Hz, but sent immediately on change
210 * windshield_wiper_status
211 * boolean, true is on
212 * 1Hz, but sent immediately on change
214 * numerical, -89.0 to 89.0 degrees with standard GPS accuracy
217 * numerical, -179.0 to 179.0 degrees with standard GPS accuracy
223 Copyright (c) 2012-2013 Ford Motor Company
225 Licensed under the BSD license.
227 [OpenXC]: http://openxcplatform.com