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@@ -7,371 +7,30 @@ 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). -## 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 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. 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 - } - } - -### 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. - -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 - -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. The `0x` prefix is - optional. - -### Diagnostic Messages - -#### Requests - -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", - "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 - 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 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. - -**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) Make this request a recurring request, at a this - frequency in Hz. To send a single non-recurring request, leave this field 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. - -#### 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 - -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"} - -**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"} - -#### Passthrough CAN Mode - -The `passthrough` command controls whether low-level CAN messages are passed -through from the CAN bus through the VI to the output stream. If the CAN -acceptance filter is in bypass mode and passthrough is enabled, the output -stream will include all received CAN messages. If the bypass filter is enabled, -only those CAN messages that have been pre-defined in the firmware are -forwarded. - -**Request** - - { "command": "passthrough", - "bus": 1, - "enabled": true - } - -**Response** - -If the bus in the request was valid and the passthrough mode was changed, the -`status` field in the response will be `true`. If `false`, the passthrough mode -was not changed. - - { "command_response": "passthrough", "status": true} - -#### Acceptance Filter Bypass - -The `af_bypass` command controls whether the CAN message acceptance filter is -bypassed for each CAN controller. By default, hardware acceptance filter (AF) is -enabled in the VI - only previously defined CAN message IDs will be received. -Send this command with `bypass: true` to force the filters to bypassed. - -If `passthrough` mode is also enabled, when the AF is bypassed, the output will -include all CAN messages received. - -**Request** - - { "command": "af_bypass", - "bus": 1, - "bypass": true - } - -**Response** - -If the bus in the request was valid and the AF mode was changed, the `status` -field in the response will be `true`. If `false`, the passthrough mode was not -changed. - - { "command_response": "af_bypass", "status": true} - -#### Payload Format Control - -The `payload_format` command determines the format for output data from the VI -and the expected format of commands sent to the VI. - -Valid formats are `json` and `protobuf`. - -**Request** - - { "command": "payload_format", - "format": "json" - } - -**Response** - -If the format was changed successfully, the `status` in the response will be -`true`. The response will be in the original message format, and all subsequent -messages will be in the new format. - - { "command_response": "payload_format", "status": true} - -#### Automatic Pre-Defined OBD-II PID Requests - -The `predefined_obd2` command enables and disables the querying for and -translating of a set of pre-defined OBD-II PIDs from the attached vehicle. When -enabled, the VI will query the vehicle to see if these PIDs are claimed to be -supported and for those that are, it will set up recurring requests. The -responses will be output as simple vehicle messages, with the names defined in -the "Signals Defined from Diagnostic Messages" section below. - -**Request** - - { "command": "predefined_obd2", - "enabled": true - } +## Binary (Protocol Buffers) -**Response** +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. -f the predefined requests were enabled or disabled successfully, the `status` in -the response will be `true`. +The binary messages are published by the VI using the standard length-delimited +method (any protobuf library should support this). - { "command_response": "predefined_obd2", "status": true} +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 +## Trace File Format An OpenXC vehicle trace file is a plaintext file that contains JSON objects, separated by newlines (which may be either `\r\n` or `\n`, depending on the @@ -472,7 +131,7 @@ manufacturers may support custom message names. * numerical, -179.0 to 179.0 degrees with standard GPS accuracy * 1Hz -### Signals from Diagnostic 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). |