diff options
Diffstat (limited to 'README.md')
| -rw-r--r-- | README.md | 219 |
1 files changed, 18 insertions, 201 deletions
@@ -1,217 +1,34 @@ # OpenXC Message Format Specification -Version: v0.3 +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 or Protocol Buffers (protobuf). -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. +## JSON -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). +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. -## Single Valued +The JSON format is best for most developers, as it is fairly efficient and very +flexible. -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. +## Binary (Protocol Buffers) -The expected format of a single valued message is: +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. - {"name": "steering_wheel_angle", "value": 45} +The binary messages are published by the VI using the standard length-delimited +method (any protobuf library should support this). -## 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 - -The format for a raw CAN message: - - {"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). - -**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", - "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). - -**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. - -**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. - -**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. - -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. - -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: - - {"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. - -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"} +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. ## Trace File Format @@ -314,7 +131,7 @@ manufacturers may support custom message names. * numerical, -179.0 to 179.0 degrees with standard GPS accuracy * 1Hz -### Signals from Diagnostics Messages +## 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). |