# OpenXC Message Format Specification
+Version: v0.4-dev
+
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.
+interfaces (e.g. USB or Bluetooth) as JSON or Protocol Buffers (protobuf).
+
+## Binary (Protocol Buffers)
+
+The Protocol Buffer format is specified in the file `openxc.proto`. Those are
+published using the standard length-delimited method (any protobuf library
+should support this).
+
+## JSON
+
+This document describes the JSON format and includes a high level description of
+each type and field. Each JSON message published by a VI is delimited with a
+`\0` character.
-There are two valid message types - single valued and evented.
+### Single Valued
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
+### Evented
The expected format of an event message is:
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
+### 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:
+The format for a raw CAN message:
- {"bus": 1, "id": 1234, "value": "0x12345678"}
+ {"bus": 1, "id": 1234, "data": "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).
**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
-
-### Requests
-
- {"bus": 1,
- "id": 1234,
- "mode": 1,
- "pid": 5,
- "payload": "0x1234",
- "parse_payload": true,
- "factor": 1.0,
- "offset": 0,
- "frequency": 0}
+ 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",
+ "multiple_responses": false,
+ "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).
**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.
+
+**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.
+
+**frequency** - (optional, defaults to 0) The frequency in Hz to send this
+ request. To send a single non-recurring request, set this to 0 or leave it
+ out.
-**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'.
+**decoded_type** - (optional, defaults to "obd2" if the request is a recognized
+OBD-II mode 1 request, otherwise "none") If specified, the valid values are
+`"none"` and `"obd2"`. If `obd2`, the payload will be decoded according to the
+OBD-II specification and returned in the `value` field. Set this to `none` to
+manually override the OBD-II decoding feature for a known PID.
-**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`.
+A diagnostic request's `bus`, `id`, `mode` and `pid` (or lack of a `pid`)
+combine to create a unique key to identify a recurring request. This means that
+you cannot simultaneosly have recurring requests at 2Hz and 5Hz for the same PID
+from the same ID.
-**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`.
+If you send a new `diagnostic_request` command with a `bus + id + mode + pid`
+key matching an existing recurring request, it will update it with whatever
+other parameters you've provided (e.g. it will change the frequency if you
+specify one).
-**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.
+To cancel a recurring request, send a `diagnostic_request` command with the
+matching request information (i.e. the `bus`, `id`, `mode` and `pid`) but a
+frequency of 0.
-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
+Non-recurring requests may have the same `bus+id+mode(+pid)` key as a recurring
+request, and they will co-exist without issue. As soon as a non-recurring
+request is either completed or times out, it is removed from the active list.
-If you're just requesting a PID, you can use a simplified format for the
-request:
+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
+#### Responses
+
+The response to a successful request:
{"bus": 1,
"id": 1234,
"mode": 1,
"pid": 5,
"success": true,
- "negative_response_code": 17,
"payload": "0x1234",
- "parsed_payload": 4660}
+ "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.
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.
+ payload interpreted as an integer.
The response to a simple PID request would look like this:
- {"bus": 1, "id": 1234, "mode": 1, "pid": 5, "payload": "0x2"}
+ {"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)"}
-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
+#### Device ID Query
-## Trace File Format
+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.
+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 Diagnostics 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