# OpenXC Message Format Specification
+Version: v0.6.0
+
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
-engine timing CAN signals may be summarized in an "engine performance" metric on
-the abstract side of the interface.
-
-## Single Valued
-
-The expected format of a single valued message is:
-
- {"name": "steering_wheel_angle", "value": 45}
-
-## Evented
-
-The expected format of an event message is:
-
- {"name": "button_event", "value": "up", "event": "pressed"}
-
-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.
-
-## Diagnostic Messages
+interfaces (e.g. USB or Bluetooth) as JSON or Protocol Buffers (protobuf).
-### Requests
+## JSON
- {"bus": 1,
- "id": 1234,
- "mode": 1,
- "pid": 5,
- "payload": "0x1234",
- "frequency": 0}
+The JSON format is the most flexible and easiest to use. The format is fully
+specified in the [JSON.mkd](JSON.mkd) file in this repository.
+a more flexible option than binary, but is less compact and
+therefore takes more bandwidth and processing power.
-**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).
+The JSON format is best for most developers, as it is fairly efficient and very
+flexible.
-**id** - the CAN arbitration ID for the request.
+## Binary (Protocol Buffers)
-**mode** - the OBD-II mode of the request - 0x1 through 0xf (0x1 through 0xa
- are the standardized modes).
+The binary format is encoded using [Google Protocol
+Buffers](https://code.google.com/p/protobuf/). The format is specified in the
+file [openxc.proto](openxc.proto). The descriptions of the messages can be foud
+in the JSON specs - the binary format mirrors this.
-**pid** - (optional) the PID for the request, if applicable.
+The binary messages are published by the VI using the standard length-delimited
+method (any protobuf library should support this).
-**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.
+The binary format is best if you need to maximize the amount of data that can be
+sent from the VI, trading off flexibility for efficiency.
-**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.
+## Message Pack
+MessagePack is an efficient binary serialization format. It lets you exchange data
+among multiple languages like JSON, but it's faster and smaller. Small integers are
+encoded into a single byte, and typical short strings require only one extra byte
+in addition to the strings themselves
-TODO it'd be nice to have the OBD-II PIDs built in, with the proper conversion
-functions - that may need a different output format
+For protocol specification visit:
+https://github.com/msgpack/msgpack/blob/master/spec.md
-If you're just requesting a PID, you can use a simplified format for the
-request:
+We are using the following lib:
+https://github.com/camgunz/cmp
- {"bus": 1, "id": 1234, "mode": 1, "pid": 5}
-
-### Responses
-
- {"bus": 1,
- "id": 1234,
- "mode": 1,
- "pid": 5,
- "success": true,
- "negative_response_code": 17,
- "payload": "0x1234"}
-
-**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 requsted node returned an error,
- `success` will be `false` and this field will contain the negative response
- code (NRC).
-
-**payload** - (optional) up to 7 bytes of data returned in the response,
- 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.
-
-The response to a simple PID requset would look like this:
-
- {"bus": 1, "id": 1234, "mode": 1, "pid": 5, "payload": "0x2"}
-
-TODO again, it'd be nice to have the OBD-II PIDs built in, with the proper
-conversion functions so the response here included the actual transformed value
-of the pid and a human readable name
+MessagePack provides a binary alternative to ProtoBuf. There are pros & cons to each
+so you can decide what works best for your project.
## Trace File Format
An OpenXC vehicle trace file is a plaintext file that contains JSON objects,
-separated by newlines.
+separated by newlines (which may be either `\r\n` or `\n`, depending on the
+platform the trace file was recorded).
The first line may be a metadata object, although this is optional:
* 1Hz, but sent immediately on change
* transmission_gear_position
* states: first, second, third, fourth, fifth, sixth, seventh, eighth,
- reverse, neutral
+ ninth, tenth, reverse, neutral
* 1Hz, but sent immediately on change
* gear_lever_position
* states: neutral, park, reverse, drive, sport, low, first, second, third,
- fourth, fifth, sixth
+ fourth, fifth, sixth, seventh, eighth, ninth, tenth
* 1Hz, but sent immediately on change
* odometer
* Numerical, km
* numerical, -179.0 to 179.0 degrees with standard GPS accuracy
* 1Hz
+## Signals from Diagnostic Messages
+
+This set of signals is often retreived from OBD-II requests. The units can be
+found in the [OBD-II standard](http://en.wikipedia.org/wiki/OBD-II_PIDs#Mode_01).
+
+* engine_load
+* engine_coolant_temperature
+* barometric_pressure
+* commanded_throttle_position
+* throttle_position
+* fuel_level
+* intake_air_temperature
+* intake_manifold_pressure
+* running_time
+* fuel_pressure
+* mass_airflow
+* accelerator_pedal_position
+* ethanol_fuel_percentage
+* engine_oil_temperature
+* engine_torque
+
License
=======
-Copyright (c) 2012-2013 Ford Motor Company
+Copyright (c) 2012-2014 Ford Motor Company
Licensed under the BSD license.
Code Review / apps / agl-service-can-low-level.git / blobdiff