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I/O, Data Format and Commands

The OpenXC message format is specified and versioned separately from any of the individual OpenXC interfaces or libraries, in the OpenXC Message Format repository.

Commands

The firmware supports all commands defined in the OpenXC Message Format specification. Both UART and USB interfaces accept commands (serialized as JSON) sent in the normal data stream back to the VI.

The payload format of the commands is specified in the OpenXC Message Format and will not be repeated here.

The tools from the OpenXC Python library can send all of these commands and are a good way to get started. Examples of the terminal commands to use are included here.

Simple Vehicle Message Writes

Simple vehicle message write commands require that the firmware is pre-configured to understand the named signal, and also allows it to be written.

openxc-control write --name seat_position --value 20

CAN Message Writes

The CAN message write requires that the VI is configured to allow raw writes to the given CAN bus. If the bus attribute is omitted, it will write the message to the first CAN bus found that permits writes.

openxc-control write --bus 1 --id 1234 --value 0x12345678

Diagnostic Requests

The diagnostic request command requires that the VI is configured to allow raw writes to the given CAN bus (with the raw_writable flag in the config file). If the bus attribute is omitted, it will write the message to the first CAN bus found that permits writes.

openxc-diag --bus 1 --id 1234 --mode 1 --pid 5

Version Query

openxc-control version

Device ID Query

openxc-control id

Platform Query

openxc-control platform

Set CAN Message Passthrough Status

openxc-control set --passthrough --bus 1

Set CAN Acceptance Filter Bypass

openxc-control set --af-bypass --bus 1

Set Payload Format

openxc-control set --new-payload-format protobuf

UART (Serial, Bluetooth)

The UART (or serial) connection for a VI is often connected to a Bluetooth module, e.g. the Roving Networks RN-41 on the Ford Reference VI. This allows wireless I/O with the VI.

The VI will send all messages it is configured to received out over the UART interface using the OpenXC message format. The data may be serialized as either JSON or protocol buffers, depending on the selected output format. Each message is followed by a \0 delimiter.

The UART interface also accepts all valid OpenXC commands. JSON is the only support format for commands in this version. Commands must be delimited with a \0 (NULL) character.

For details on your particular platform (i.e. the baud rate and pins for UART on the board) see the :doc:`supported platforms </platforms/platforms>`.

USB Device

The VI is configured as a USB device, so you can connect it to a computer or mobile device that supports USB OTG. USB is best if you need to stream a lot of to or from the VI - the UART connection caps out at around 23KB/s, but USB can go about 100KB/s.

The VI will publish all messages it is configured to received to USB bulk IN endpoint 2 using the OpenXC message format. The data may be serialized as either JSON or protocol buffers, depending on the selected output format. Each message is followed by a \0 delimiter. A larger read request from the host request will allow more messages to be batched together into one USB request and give high overall throughput (with the downside of introducing delay depending on the size of the request).

Bulk OUT endpoint 5 will accept valid OpenXC commands from the host, serialized as JSON (the Protocol Buffer format is not supported for commands). Commands must be delimited with a \0 (NULL) character. Commands must be no more than 256 bytes (4 USB packets).

Finally, the VI publishes log messages to bulk IN endpoint 11 when compiled with the DEBUG flag. The log messages are delimited with \0.

If you are using one of the support libraries (e.g. openxc-python or openxc-android, you don't need to worry about the details of the USB device driver, but for creating new libraries the endpoints are documented here.

Control Transfers

Transfer request type: 0x83

The VI accepts USB control requests on the standard endpoint 0 where the payload is a standard OpenXC message format command meessage (e.g. version, device ID, or diagnostic request, etc).

The responses are injected into the normal output data stream usig the same format as the :ref:`version query <version-query>`, :ref:`device ID query <device-id-query>`, etc.