# OpenXC Message Format Specification
+This specification is a part of the [OpenXC platform][OpenXC].
+
+An OpenXC vehicle interface sends generic vehicle data over one or more output
+interfaces (e.g. USB or Bluetooth) as JSON objects, separated by newlines.
+
There are two valid message types - single valued and evented.
There may not be a 1:1 relationship between input and output signals - i.e. raw
This format is good for something like a button event, where there are two
discrete pieces of information in the measurement.
+
+## Raw CAN Message format
+
+An OpenXC vehicle interface may also output raw CAN messages. Each CAN message
+is sent as a JSON object, separated by newlines. The format of each object is:
+
+ {"bus": 1, "id": 1234, "value": "0x12345678"}
+
+**bus** - the numerical identifier of the CAN bus where this message originated,
+ most likely 1 or 2 (for a vehicle interface with 2 CAN controllers).
+
+**id** - the CAN message ID
+
+**data** - up to 8 bytes of data from the CAN message's payload, represented as
+ a hexidecimal number in a string. Many JSON parser cannot handle 64-bit
+ integers, which is why we are not using a numerical data type. Each byte in
+ the string *must* be represented with 2 characters, e.g. `0x1` is `0x01` - the
+ complete string must have an even number of characters.
+
+## Diagnostic Messages
+
+### Requests
+
+A request to add or update a diagnostic request is sent to a vehicle interface
+with this command format:
+
+ { "command": "diagnostic_request",
+ "request": {
+ "bus": 1,
+ "id": 1234,
+ "mode": 1,
+ "pid": 5,
+ "payload": "0x1234",
+ "parse_payload": true,
+ "multiple_responses": false,
+ "factor": 1.0,
+ "offset": 0,
+ "frequency": 1,
+ "name": "my_pid"
+ }
+ }
+ }
+
+**bus** - the numerical identifier of the CAN bus where this request should be
+ sent, most likely 1 or 2 (for a vehicle interface with 2 CAN controllers).
+
+**id** - the CAN arbitration ID for the request.
+
+**mode** - the OBD-II mode of the request - 1 through 15 (1 through 9 are the
+ standardized modes).
+
+**pid** - (optional) the PID for the request, if applicable.
+
+**payload** - (optional) up to 7 bytes of data for the request's payload
+ represented as a hexidecimal number in a string. Many JSON parser cannot
+ handle 64-bit integers, which is why we are not using a numerical data type.
+ Each byte in the string *must* be represented with 2 characters, e.g. `0x1`
+ is `0x01` - the complete string must have an even number of characters.
+
+**parse_payload** - (optional, false by default) if `true`, the complete payload
+ in the response message will be parsed as a number and returned in the
+ `value` field of the response. The `payload` field will be omitted in
+ responses with a `value`.
+
+**name** - (optional, defaults to nothing) A human readable, string name for
+ this request. If provided, the response will have a `name` field (much like a
+ normal translated message) with this value in place of `bus`, `id`, `mode` and
+ `pid`.
+
+**multiple_responses** - (optional, false by default) if true, request will stay
+ active for a full 100ms, even after receiving a diagnostic response message.
+ This is useful for requests to the functional broadcast arbitration ID
+ (`0x7df`) when you need to get responses from multiple modules. It's possible
+ to set this to `true` for non-broadcast requests, but in practice you won't
+ see any additional responses after the first and it will just take up memory
+ in the VI for longer.
+
+**factor** - (optional, 1.0 by default) if `parse_payload` is true, the value in
+ the payload will be multiplied by this factor before returning. The `factor`
+ is applied before the `offset`.
+
+**offset** - (optional, 0 by default) if `parse_payload` is true, this offset
+ will be added to the value in the payload before returning. The `offset` is
+ applied after the `factor`.
+
+**frequency** - (optional, defaults to 0) The frequency in Hz to send this
+ request. To send a single request, set this to 0 or leave it out.
+
+The `bus+id+mode+pid` key is unique, so if you send a create request with that
+key twice, it'll overwrite the existing one (i.e. it will change the frequency,
+the only other parameter). To cancel a recurring request, send this command with
+the frequency set to 0.
+
+If you're just requesting a PID, you can use this minimal field set for the
+`request` object:
+
+ {"bus": 1, "id": 1234, "mode": 1, "pid": 5}
+
+### Responses
+
+The response to a successful request:
+
+ {"bus": 1,
+ "id": 1234,
+ "mode": 1,
+ "pid": 5,
+ "success": true,
+ "payload": "0x1234",
+ "value": 4660}
+
+and to an unsuccessful request, with the `negative_response_code` and no `pid`
+echo:
+
+ {"bus": 1,
+ "id": 1234,
+ "mode": 1,
+ "success": false,
+ "negative_response_code": 17}
+
+**bus** - the numerical identifier of the CAN bus where this response was
+ received.
+
+**id** - the CAN arbitration ID for this response.
+
+**mode** - the OBD-II mode of the original diagnostic request.
+
+**pid** - (optional) the PID for the request, if applicable.
+
+**success** - true if the response received was a positive response. If this
+ field is false, the remote node returned an error and the
+ `negative_response_code` field should be populated.
+
+**negative_response_code** - (optional) If requested node returned an error,
+ `success` will be `false` and this field will contain the negative response
+ code (NRC).
+
+Finally, the `payload` and `value` fields are mutually exclusive:
+
+**payload** - (optional) up to 7 bytes of data returned in the response,
+ represented as a hexadecimal number in a string. Many JSON parser cannot
+ handle 64-bit integers, which is why we are not using a numerical data type.
+
+**value** - (optional) if the response had a payload, this may be the
+ payload interpreted as an integer and transformed with a factor and offset
+ provided with the request.
+
+The response to a simple PID request would look like this:
+
+ {"success": true, "bus": 1, "id": 1234, "mode": 1, "pid": 5, "payload": "0x2"}
+
+## Commands
+
+### Version Query
+
+The `version` command triggers the VI to inject a firmware version identifier
+response into the outgoing data stream.
+
+**Request**
+
+ { "command": "version"}
+
+**Response**
+
+ { "command_response": "version", "message": "v6.0-dev (default)"}
+
+### Device ID Query
+
+The `device_id` command triggers the VI to inject a unique device ID (e.g. the
+MAC address of an included Bluetooth module) into into the outgoing data stream.
+
+**Request**
+
+ { "command": "device_id"}
+
+**Response**
+
+ { "command_response": "device_id", "message": "0012345678"}
+
+## Trace File Format
+
+An OpenXC vehicle trace file is a plaintext file that contains JSON objects,
+separated by newlines.
+
+The first line may be a metadata object, although this is optional:
+
+```
+{"metadata": {
+ "version": "v3.0",
+ "vehicle_interface_id": "7ABF",
+ "vehicle": {
+ "make": "Ford",
+ "model": "Mustang",
+ "trim": "V6 Premium",
+ "year": 2013
+ },
+ "description": "highway drive to work",
+ "driver_name": "TJ Giuli",
+ "vehicle_id": "17N1039247929"
+}
+```
+
+The following lines are OpenXC messages with a `timestamp` field added, e.g.:
+
+ {"timestamp": 1385133351.285525, "name": "steering_wheel_angle", "value": 45}
+
+The timestamp is in [UNIX time](http://en.wikipedia.org/wiki/Unix_time)
+(i.e. seconds since the UNIX epoch, 00:00:00 UTC, 1/1/1970).
+
+## Official Signals
+
+These signal names are a part of the OpenXC specification, although some
+manufacturers may support custom message names.
+
+* steering_wheel_angle
+ * numerical, -600 to +600 degrees
+ * 10Hz
+* torque_at_transmission
+ * numerical, -500 to 1500 Nm
+ * 10Hz
+* engine_speed
+ * numerical, 0 to 16382 RPM
+ * 10Hz
+* vehicle_speed
+ * numerical, 0 to 655 km/h (this will be positive even if going in reverse
+ as it's not a velocity, although you can use the gear status to figure out
+ direction)
+ * 10Hz
+* accelerator_pedal_position
+ * percentage
+ * 10Hz
+* parking_brake_status
+ * boolean, (true == brake engaged)
+ * 1Hz, but sent immediately on change
+* brake_pedal_status
+ * boolean (True == pedal pressed)
+ * 1Hz, but sent immediately on change
+* transmission_gear_position
+ * states: first, second, third, fourth, fifth, sixth, seventh, eighth,
+ reverse, neutral
+ * 1Hz, but sent immediately on change
+* gear_lever_position
+ * states: neutral, park, reverse, drive, sport, low, first, second, third,
+ fourth, fifth, sixth
+ * 1Hz, but sent immediately on change
+* odometer
+ * Numerical, km
+ 0 to 16777214.000 km, with about .2m resolution
+ * 10Hz
+* ignition_status
+ * states: off, accessory, run, start
+ * 1Hz, but sent immediately on change
+* fuel_level
+ * percentage
+ * 2Hz
+* fuel_consumed_since_restart
+ * numerical, 0 - 4294967295.0 L (this goes to 0 every time the vehicle
+ restarts, like a trip meter)
+ * 10Hz
+* door_status
+ * Value is State: driver, passenger, rear_left, rear_right.
+ * Event is boolean: true == ajar
+ * 1Hz, but sent immediately on change
+* headlamp_status
+ * boolean, true is on
+ * 1Hz, but sent immediately on change
+* high_beam_status
+ * boolean, true is on
+ * 1Hz, but sent immediately on change
+* windshield_wiper_status
+ * boolean, true is on
+ * 1Hz, but sent immediately on change
+* latitude
+ * numerical, -89.0 to 89.0 degrees with standard GPS accuracy
+ * 1Hz
+* longitude
+ * numerical, -179.0 to 179.0 degrees with standard GPS accuracy
+ * 1Hz
+
+License
+=======
+
+Copyright (c) 2012-2013 Ford Motor Company
+
+Licensed under the BSD license.
+
+[OpenXC]: http://openxcplatform.com