# 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 binary format is encoded using [Google Protocol
+Buffers](https://code.google.com/p/protobuf/). The format is specified in the
+file `openxc.proto`. Those are published using the standard length-delimited
+method (any protobuf library should support this).
+
+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.
+
+## 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.
+
+The JSON format is best for most developers, as it is fairly efficient and very
+flexible.
+
+### Extra Values
+
+Any of the following JSON objects may optionally include an `extras`
+field. The value may be any valid JSON object or array. The client libraries
+will do their best to parse this information into a generic format and pass it
+to your application. For example:
+
+ {"name": "steering_wheel_angle",
+ "value": 45,
+ "extras": {
+ "calibrated": false
+ }
+ }
-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.
+ 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. The `0x` prefix is
+ optional.
-## Diagnostic Messages
+### Diagnostic Messages
-### Requests
+#### Requests
-A request to add or update a diagnostic request is sent to a vehicle interface
-with this command format:
+A diagnostic request is added or cancelled with a JSON object like this example:
{ "command": "diagnostic_request",
+ "action": "add",
"request": {
"bus": 1,
"id": 1234,
"mode": 1,
"pid": 5,
"payload": "0x1234",
- "parse_payload": true,
- "multiple_response": false,
- "factor": 1.0,
- "offset": 0,
+ "multiple_responses": false,
"frequency": 1,
"name": "my_pid"
}
}
}
+* The `command` must be `diagnostic_request.`
+* The `action` must be included, and must be one of:
+ * `add` - create a new one-off or recurring diagnostic request.
+ * `cancel` - cancel an existing request.
+* The details of the request must be included in the `request` field, using
+ the sub-fields defined below.
+
+A diagnostic request's `bus`, `id`, `mode` and `pid` (or lack of a `pid`)
+combine to create a unique key to identify a request. These four fields will be
+referred to as the key of the diagnostic request. For example, to create a
+simple one-time diagnostic request:
+
+ { "command": "diagnostic_request",
+ "action": "add",
+ "request": {
+ "bus": 1,
+ "id": 1234,
+ "mode": 1,
+ "pid": 5
+ }
+ }
+ }
+
+Requests are completed after any responses are received (unless
+`multiple_responses` is set), or the request has timed out after a certain
+number of seconds. After a request is completed, you can re-`create` the same
+key to make another request.
+
+Requests with a `frequency` are added as *recurring* requests, e.g. to add the
+previous example as a recurring request at 1Hz:
+
+ { "command": "diagnostic_request",
+ "action": "add",
+ "request": {
+ "bus": 1,
+ "id": 1234,
+ "mode": 1,
+ "pid": 5,
+ "frequency": 1
+ }
+ }
+ }
+
+To cancel a recurring request, send a `cancel` action with the same key, e.g.:
+
+ { "command": "diagnostic_request",
+ "action": "cancel",
+ "request": {
+ "bus": 1,
+ "id": 1234,
+ "mode": 1,
+ "pid": 5
+ }
+ }
+ }
+
+Simultaneous recurring requests for the same key at different rates (e.g. 1Hz
+*and* 2Hz) is not supported. However, non-recurring ("one-off") requests may
+exist in parallel with a recurring request for the same key.
+
**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).
+**mode** - the OBD-II mode of the request - 0x1 through 0xff (1 through 9 are the
+ standardized modes and 0x22 is a common proprietary mode).
**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
+ 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.
+ 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. The
+ `0x` prefix is optional.
-**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_response** - (optional, false by default) if true, request will stay
+**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
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.
-
-**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) in place of the request details (i.e. the bus,
- id, mode and pid). TODO elaborate on this.
-
-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.
-
-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
+**frequency** - (optional) Make this request a recurring request, at a this
+ frequency in Hz. To send a single non-recurring request, leave this field out.
-If you're just requesting a PID, you can use this minimal field set for the
-`request` object:
+**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.
- {"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
+
+In addition to the `diagnostic_request` command described earlier, there are
+other possible values for the `command` field.
+
+#### Version Query
+
+The `version` command triggers the VI to inject a firmware version identifier
+response into the outgoing data stream.
+
+**Request**
+
+ { "command": "version"}
-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
+**Response**
-## Trace File Format
+ { "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"}
+
+#### Passthrough CAN Mode
+
+The `passthrough` command controls the passthrough mode for each of the CAN
+buses. There are three passthrough modes:
+
+* `off` - Only the specified simple vehicle messages are processed and output
+ from the VI.
+* `filtered` - If the CAN acceptance filter is not otherwise disabled, only the
+ pre-defined CAN messages (i.e. those compiled with the firmware) will be
+ output in the low-level CAN format from VI.
+* `unfiltered` - All received CAN messages will be passed through from the bus
+ to the VI's output.
+
+**Request**
+
+ { "command": "passthrough"
+ "bus": 1,
+ "mode":
+ }
+
+**Response**
+
+If the bus and mode in the request were recognized, the `status` field in the
+response will be `true`. If `false`, the passthrough mode was not changed.
+
+ { "command_response": "passthrough", "status": true}
+
+### 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 / low-level-can-service.git / blobdiff