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).
-There are two valid message types - single valued and evented.
+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.
+
+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).
+
+## 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}
## 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"}
"mode": 1,
"pid": 5,
"payload": "0x1234",
- "parse_payload": true,
"multiple_responses": false,
"factor": 1.0,
"offset": 0,
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
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`.
+**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.
-**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`.
+**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.
-**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.
+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.
-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 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).
+
+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.
+
+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 this minimal field set for the
`request` object:
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:
## 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:
* 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 / low-level-can-service.git / blobdiff