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diff --git a/JSON.mkd b/JSON.mkd new file mode 100644 index 00000000..7bf0ce5a --- /dev/null +++ b/JSON.mkd @@ -0,0 +1,353 @@ +# OpenXC JSON Message Format + +Each JSON message published by a VI is delimited with a `\0 ` character. + +## 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 + } + } + +## Simple Vehicle Message + +There may not be a 1:1 relationship between input and output signals - i.e. +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 Simple Vehicle Message + +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. + +## CAN Message + +The format for a plain 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. + +**format** - (optional) explicitly set the frame format for the CAN message, one + of `standard` or `extended`. If the `id` is greater than `0x7ff`, the extended + frame format will be selected automatically. + +## 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 + simple vehicle 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 + } + +**Response** + +f the predefined requests were enabled or disabled successfully, the `status` in +the response will be `true`. + + { "command_response": "predefined_obd2", "status": true} + |