1 # OpenXC JSON Message Format
3 Each JSON message published by a VI is delimited with a `\0 ` character.
6 1. [Vehicle Messages](#vehicle-messages)
7 2. [CAN Message](#can-message)
8 3. [Diagnostic Message](#diagnostic-message)
9 4. [Commands](#commands)
10 5. [Extra Values](#extra-values)
14 ### Simple Vehicle Message
16 There may not be a 1:1 relationship between input and output signals - i.e.
17 engine timing CAN signals may be summarized in an "engine performance" metric on
18 the abstract side of the interface.
20 The expected format of a single valued message is:
22 {"name": "steering_wheel_angle", "value": 45}
24 ### Evented Simple Vehicle Message
26 The expected format of an event message is:
28 {"name": "button_event", "value": "up", "event": "pressed"}
30 This format is good for something like a button event, where there are two
31 discrete pieces of information in the measurement.
35 The format for a plain CAN message:
37 {"bus": 1, "id": 1234, "data": "0x12345678"}
39 **bus** - the numerical identifier of the CAN bus where this message originated,
40 most likely 1 or 2 (for a vehicle interface with 2 CAN controllers).
42 **id** - the CAN message ID
44 **data** - up to 8 bytes of data from the CAN message's payload, represented as
45 a hexidecimal number in a string. Many JSON parser cannot handle 64-bit
46 integers, which is why we are not using a numerical data type. Each byte in
47 the string *must* be represented with 2 characters, e.g. `0x1` is `0x01` - the
48 complete string must have an even number of characters. The `0x` prefix is
51 **format** - (optional) explicitly set the frame format for the CAN message, one
52 of `standard` or `extended`. If the `id` is greater than `0x7ff`, the extended
53 frame format will be selected automatically.
59 A diagnostic request is added or cancelled with a JSON object like this example:
61 { "command": "diagnostic_request",
63 "diagnostic_request": {
69 "multiple_responses": false,
76 * The `command` must be `diagnostic_request.`
77 * The `action` must be included, and must be one of:
78 * `add` - create a new one-off or recurring diagnostic request.
79 * `cancel` - cancel an existing request.
80 * The details of the request must be included in the `request` field, using
81 the sub-fields defined below.
83 A diagnostic request's `bus`, `id`, `mode` and `pid` (or lack of a `pid`)
84 combine to create a unique key to identify a request. These four fields will be
85 referred to as the key of the diagnostic request. For example, to create a
86 simple one-time diagnostic request:
88 { "command": "diagnostic_request",
90 "diagnostic_request": {
99 Requests are completed after any responses are received (unless
100 `multiple_responses` is set), or the request has timed out after a certain
101 number of seconds. After a request is completed, you can re-`create` the same
102 key to make another request.
104 Requests with a `frequency` are added as *recurring* requests, e.g. to add the
105 previous example as a recurring request at 1Hz:
107 { "command": "diagnostic_request",
109 "diagnostic_request": {
119 To cancel a recurring request, send a `cancel` action with the same key, e.g.:
121 { "command": "diagnostic_request",
123 "diagnostic_request": {
132 Simultaneous recurring requests for the same key at different rates (e.g. 1Hz
133 *and* 2Hz) is not supported. However, non-recurring ("one-off") requests may
134 exist in parallel with a recurring request for the same key.
136 **bus** - the numerical identifier of the CAN bus where this request should be
137 sent, most likely 1 or 2 (for a vehicle interface with 2 CAN controllers).
139 **message_id** - the CAN message ID for the request.
141 **mode** - the OBD-II mode of the request - 0x1 through 0xff (1 through 9 are the
142 standardized modes and 0x22 is a common proprietary mode).
144 **pid** - (optional) the PID for the request, if applicable.
146 **payload** - (optional) up to 7 bytes of data for the request's payload
147 represented as a hexadecimal number in a string. Many JSON parser cannot
148 handle 64-bit integers, which is why we are not using a numerical data type.
149 Each byte in the string *must* be represented with 2 characters, e.g. `0x1`
150 is `0x01` - the complete string must have an even number of characters. The
151 `0x` prefix is optional.
153 **name** - (optional, defaults to nothing) A human readable, string name for
154 this request. If provided, the response will have a `name` field (much like a
155 simple vehicle message) with this value in place of `bus`, `id`, `mode` and
158 **multiple_responses** - (optional, false by default) if true, request will stay
159 active for a full 100ms, even after receiving a diagnostic response message.
160 This is useful for requests to the functional broadcast message ID
161 (`0x7df`) when you need to get responses from multiple modules. It's possible
162 to set this to `true` for non-broadcast requests, but in practice you won't
163 see any additional responses after the first and it will just take up memory
164 in the VI for longer.
166 **frequency** - (optional) Make this request a recurring request, at a this
167 frequency in Hz. To send a single non-recurring request, leave this field out.
169 **decoded_type** - (optional, defaults to "obd2" if the request is a recognized
170 OBD-II mode 1 request, otherwise "none") If specified, the valid values are
171 `"none"` and `"obd2"`. If `obd2`, the payload will be decoded according to the
172 OBD-II specification and returned in the `value` field. Set this to `none` to
173 manually override the OBD-II decoding feature for a known PID.
177 Requests to add or cancel a diagnostic request are first acknowledged by the VI,
178 before any responses to the request are returned. The response uses the standard
179 command response format:
181 { "command_response": "diagnostic_request", "status": true}
183 **status** - true if the request was successfully created or cancelled.
185 When a node on the network response to the request and the result is published
186 by the VI, the result looks like:
196 and to an unsuccessful request, with the `negative_response_code` and no `pid`
203 "negative_response_code": 17}
205 **bus** - the numerical identifier of the CAN bus where this response was
208 **message_id** - the CAN message ID for this response.
210 **mode** - the OBD-II mode of the original diagnostic request.
212 **pid** - (optional) the PID for the request, if applicable.
214 **success** - true if the response received was a positive response. If this
215 field is false, the remote node returned an error and the
216 `negative_response_code` field should be populated.
218 **negative_response_code** - (optional) If requested node returned an error,
219 `success` will be `false` and this field will contain the negative response
222 Finally, the `payload` and `value` fields are mutually exclusive:
224 **payload** - (optional) up to 7 bytes of data returned in the response,
225 represented as a hexadecimal number in a string. Many JSON parser cannot
226 handle 64-bit integers, which is why we are not using a numerical data type.
228 **value** - (optional) if the response had a payload, this may be the
229 payload interpreted as an integer.
231 The response to a simple PID request would look like this:
233 {"success": true, "bus": 1, "message_id": 1234, "mode": 1, "pid": 5, "payload": "0x2"}
237 In addition to the `diagnostic_request` command described earlier, there are
238 other possible values for the `command` field.
240 All commands immediately return a `command_response`, e.g.:
242 { "command_response": "version", "message": "v6.0-dev (default)", "status": true}
244 **command_response** - an echo of the command this is a ACKing.
246 **status** - true if the command was understood and performed succesfully.
248 **message** - (optional) a string message from the VI, e.g. to return a version
249 descriptor or error message.
253 The `version` command triggers the VI to inject a firmware version identifier
254 response into the outgoing data stream.
258 { "command": "version"}
262 { "command_response": "version", "message": "v6.0-dev (default)", "status": true}
266 The `device_id` command triggers the VI to inject a unique device ID (e.g. the
267 MAC address of an included Bluetooth module) into into the outgoing data stream.
269 If no device ID is available, the response message will be "Unknown".
273 { "command": "device_id"}
277 { "command_response": "device_id", "message": "0012345678", "status": true}
279 ### Passthrough CAN Mode
281 The `passthrough` command controls whether low-level CAN messages are passed
282 through from the CAN bus through the VI to the output stream. If the CAN
283 acceptance filter is in bypass mode and passthrough is enabled, the output
284 stream will include all received CAN messages. If the bypass filter is enabled,
285 only those CAN messages that have been pre-defined in the firmware are
290 { "command": "passthrough",
297 If the bus in the request was valid and the passthrough mode was changed, the
298 `status` field in the response will be `true`. If `false`, the passthrough mode
301 { "command_response": "passthrough", "status": true}
303 ### Acceptance Filter Bypass
305 The `af_bypass` command controls whether the CAN message acceptance filter is
306 bypassed for each CAN controller. By default, hardware acceptance filter (AF) is
307 enabled in the VI - only previously defined CAN message IDs will be received.
308 Send this command with `bypass: true` to force the filters to bypassed.
310 If `passthrough` mode is also enabled, when the AF is bypassed, the output will
311 include all CAN messages received.
315 { "command": "af_bypass",
322 If the bus in the request was valid and the AF mode was changed, the `status`
323 field in the response will be `true`. If `false`, the passthrough mode was not
326 { "command_response": "af_bypass", "status": true}
328 ### Payload Format Control
330 The `payload_format` command determines the format for output data from the VI
331 and the expected format of commands sent to the VI.
333 Valid formats are `json` and `protobuf`.
337 { "command": "payload_format",
343 If the format was changed successfully, the `status` in the response will be
344 `true`. The response will be in the original message format, and all subsequent
345 messages will be in the new format.
347 { "command_response": "payload_format", "status": true}
349 ### Automatic Pre-Defined OBD-II PID Requests
351 The `predefined_obd2` command enables and disables the querying for and
352 translating of a set of pre-defined OBD-II PIDs from the attached vehicle. When
353 enabled, the VI will query the vehicle to see if these PIDs are claimed to be
354 supported and for those that are, it will set up recurring requests. The
355 responses will be output as simple vehicle messages, with the names defined in
356 the "Signals Defined from Diagnostic Messages" section below.
360 { "command": "predefined_obd2",
366 If the predefined requests were enabled or disabled successfully, the `status` in
367 the response will be `true`.
369 { "command_response": "predefined_obd2", "status": true}
371 ### C5 Cellular Configuration
373 The ModemConfigurationCommand message allows users to change certain aspects of modem operation on-the-fly (at runtime). The modem configuration settings are stored in flash memory and are untouched by the bootloader during a software update (assuming the correct cellular_c5 linker file is used during compilation of vi-firmware). Thus, new modem settings persistent across power cycles.
375 The ModemConfigurationCommand message provides three sub-messages for particular groups of modem settings. These are NetworkOperatorSettings, NetworkDataSettings, and ServerConnectSettings. These configuration messages are described in great detail within the [c5_cellular_config](https://github.com/openxc/vi-firmware/docs/advanced/c5_cell_config.html) documentation.
377 Currently, only the ServerConnectSettings sub-message is supported in the vi-firmware's command interpreter. All other settings are currently compile-time only.
379 The ServerConnectSettings part of ModemConfigurationCommand allows the user to set the host server name and port that the device will use when opening a TCP socket to upload data. This destination must be running an HTTP server similar to [OpenXCWebServer](https://github.com/openxc/openxc-azure-webserver), which defines a set of supported HTTP transactions where the body is comprised of data in the familiar OpenXC Message Format.
383 { "command": "modem_configuration",
385 "host": "www.myhost.com",
392 { "command_response": "modem_configuration", "status": true}
396 In order to check the status of the SD card, the following command is available:
398 { "command": "sd_mount_status"}
400 Command response if the SD card is mounted correctly:
402 { "command_response": "sd_mount_status", "status": true}
404 If the SD card is full, not enabled, or connected as a MSD, the device will respond with:
406 { "command_response": "sd_mount_status", "status": false}
408 For more info see [c5_msd](https://github.com/openxc/vi-firmware/docs/advanced/msd.html).
410 ## C5 RTC Configuration
412 To set the current time of the RTC, the following
414 { "command": "rtc_configuration", "unix_time": "1448551563"}
418 { "command_response": "rtc_configuration", "status": true}
420 For more info see [c5_rtc](https://github.com/openxc/vi-firmware/docs/advanced/rtc.html).
424 Any of the following JSON objects may optionally include an `extras`
425 field. The value may be any valid JSON object or array. The client libraries
426 will do their best to parse this information into a generic format and pass it
427 to your application. For example:
429 {"name": "steering_wheel_angle",