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).
12 The JSON format is the most flexible and easiest to use. The format is fully
13 specified in the [JSON.mkd](JSON.mkd) file in this repository.
14 a more flexible option than binary, but is less compact and
15 therefore takes more bandwidth and processing power.
17 The JSON format is best for most developers, as it is fairly efficient and very
20 ## Binary (Protocol Buffers)
22 The binary format is encoded using [Google Protocol
23 Buffers](https://code.google.com/p/protobuf/). The format is specified in the
24 file [openxc.proto](openxc.proto). The descriptions of the messages can be foud
25 in the JSON specs - the binary format mirrors this.
27 The binary messages are published by the VI using the standard length-delimited
28 method (any protobuf library should support this).
30 The binary format is best if you need to maximize the amount of data that can be
31 sent from the VI, trading off flexibility for efficiency.
34 MessagePack is an efficient binary serialization format. It lets you exchange data
35 among multiple languages like JSON. But it's faster and smaller. Small integers are
36 encoded into a single byte, and typical short strings require only one extra byte
37 in addition to the strings themselves
39 For protocol specification visit
40 https://github.com/msgpack/msgpack/blob/master/spec.md
44 An OpenXC vehicle trace file is a plaintext file that contains JSON objects,
45 separated by newlines (which may be either `\r\n` or `\n`, depending on the
46 platform the trace file was recorded).
48 The first line may be a metadata object, although this is optional:
53 "vehicle_interface_id": "7ABF",
60 "description": "highway drive to work",
61 "driver_name": "TJ Giuli",
62 "vehicle_id": "17N1039247929"
66 The following lines are OpenXC messages with a `timestamp` field added, e.g.:
68 {"timestamp": 1385133351.285525, "name": "steering_wheel_angle", "value": 45}
70 The timestamp is in [UNIX time](http://en.wikipedia.org/wiki/Unix_time)
71 (i.e. seconds since the UNIX epoch, 00:00:00 UTC, 1/1/1970).
75 These signal names are a part of the OpenXC specification, although some
76 manufacturers may support custom message names.
78 * steering_wheel_angle
79 * numerical, -600 to +600 degrees
81 * torque_at_transmission
82 * numerical, -500 to 1500 Nm
85 * numerical, 0 to 16382 RPM
88 * numerical, 0 to 655 km/h (this will be positive even if going in reverse
89 as it's not a velocity, although you can use the gear status to figure out
92 * accelerator_pedal_position
95 * parking_brake_status
96 * boolean, (true == brake engaged)
97 * 1Hz, but sent immediately on change
99 * boolean (True == pedal pressed)
100 * 1Hz, but sent immediately on change
101 * transmission_gear_position
102 * states: first, second, third, fourth, fifth, sixth, seventh, eighth,
103 ninth, tenth, reverse, neutral
104 * 1Hz, but sent immediately on change
105 * gear_lever_position
106 * states: neutral, park, reverse, drive, sport, low, first, second, third,
107 fourth, fifth, sixth, seventh, eighth, ninth, tenth
108 * 1Hz, but sent immediately on change
111 0 to 16777214.000 km, with about .2m resolution
114 * states: off, accessory, run, start
115 * 1Hz, but sent immediately on change
119 * fuel_consumed_since_restart
120 * numerical, 0 - 4294967295.0 L (this goes to 0 every time the vehicle
121 restarts, like a trip meter)
124 * Value is State: driver, passenger, rear_left, rear_right.
125 * Event is boolean: true == ajar
126 * 1Hz, but sent immediately on change
128 * boolean, true is on
129 * 1Hz, but sent immediately on change
131 * boolean, true is on
132 * 1Hz, but sent immediately on change
133 * windshield_wiper_status
134 * boolean, true is on
135 * 1Hz, but sent immediately on change
137 * numerical, -89.0 to 89.0 degrees with standard GPS accuracy
140 * numerical, -179.0 to 179.0 degrees with standard GPS accuracy
143 ## Signals from Diagnostic Messages
145 This set of signals is often retreived from OBD-II requests. The units can be
146 found in the [OBD-II standard](http://en.wikipedia.org/wiki/OBD-II_PIDs#Mode_01).
149 * engine_coolant_temperature
150 * barometric_pressure
151 * commanded_throttle_position
154 * intake_air_temperature
155 * intake_manifold_pressure
159 * accelerator_pedal_position
160 * ethanol_fuel_percentage
161 * engine_oil_temperature
167 Copyright (c) 2012-2014 Ford Motor Company
169 Licensed under the BSD license.
171 [OpenXC]: http://openxcplatform.com