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
38 For protocol specification visit https://github.com/msgpack/msgpack/blob/master/spec.md
42 An OpenXC vehicle trace file is a plaintext file that contains JSON objects,
43 separated by newlines (which may be either `\r\n` or `\n`, depending on the
44 platform the trace file was recorded).
46 The first line may be a metadata object, although this is optional:
51 "vehicle_interface_id": "7ABF",
58 "description": "highway drive to work",
59 "driver_name": "TJ Giuli",
60 "vehicle_id": "17N1039247929"
64 The following lines are OpenXC messages with a `timestamp` field added, e.g.:
66 {"timestamp": 1385133351.285525, "name": "steering_wheel_angle", "value": 45}
68 The timestamp is in [UNIX time](http://en.wikipedia.org/wiki/Unix_time)
69 (i.e. seconds since the UNIX epoch, 00:00:00 UTC, 1/1/1970).
73 These signal names are a part of the OpenXC specification, although some
74 manufacturers may support custom message names.
76 * steering_wheel_angle
77 * numerical, -600 to +600 degrees
79 * torque_at_transmission
80 * numerical, -500 to 1500 Nm
83 * numerical, 0 to 16382 RPM
86 * numerical, 0 to 655 km/h (this will be positive even if going in reverse
87 as it's not a velocity, although you can use the gear status to figure out
90 * accelerator_pedal_position
93 * parking_brake_status
94 * boolean, (true == brake engaged)
95 * 1Hz, but sent immediately on change
97 * boolean (True == pedal pressed)
98 * 1Hz, but sent immediately on change
99 * transmission_gear_position
100 * states: first, second, third, fourth, fifth, sixth, seventh, eighth,
101 ninth, tenth, reverse, neutral
102 * 1Hz, but sent immediately on change
103 * gear_lever_position
104 * states: neutral, park, reverse, drive, sport, low, first, second, third,
105 fourth, fifth, sixth, seventh, eighth, ninth, tenth
106 * 1Hz, but sent immediately on change
109 0 to 16777214.000 km, with about .2m resolution
112 * states: off, accessory, run, start
113 * 1Hz, but sent immediately on change
117 * fuel_consumed_since_restart
118 * numerical, 0 - 4294967295.0 L (this goes to 0 every time the vehicle
119 restarts, like a trip meter)
122 * Value is State: driver, passenger, rear_left, rear_right.
123 * Event is boolean: true == ajar
124 * 1Hz, but sent immediately on change
126 * boolean, true is on
127 * 1Hz, but sent immediately on change
129 * boolean, true is on
130 * 1Hz, but sent immediately on change
131 * windshield_wiper_status
132 * boolean, true is on
133 * 1Hz, but sent immediately on change
135 * numerical, -89.0 to 89.0 degrees with standard GPS accuracy
138 * numerical, -179.0 to 179.0 degrees with standard GPS accuracy
141 ## Signals from Diagnostic Messages
143 This set of signals is often retreived from OBD-II requests. The units can be
144 found in the [OBD-II standard](http://en.wikipedia.org/wiki/OBD-II_PIDs#Mode_01).
147 * engine_coolant_temperature
148 * barometric_pressure
149 * commanded_throttle_position
152 * intake_air_temperature
153 * intake_manifold_pressure
157 * accelerator_pedal_position
158 * ethanol_fuel_percentage
159 * engine_oil_temperature
165 Copyright (c) 2012-2014 Ford Motor Company
167 Licensed under the BSD license.
169 [OpenXC]: http://openxcplatform.com