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// Copyright (C) 2017 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only
/*!
\page qtcanbus-backends.html
\title Qt CAN Bus
\brief Implemented Qt CAN Bus.
A Controller Area Network (CAN) is a vehicle bus standard designed to allow microcontrollers
and devices to communicate with each other in applications without a host computer.
\section1 Overview
It is a message-based protocol, designed originally for multiplex electrical wiring within
automobiles, but is also used in many other contexts.
The CAN Bus API provides some common API to access the CAN devices:
\list
\li QCanBus provides an API to create a QCanBusDevice from a chosen plugin.
\li QCanBusDeviceInfo provides information about available CAN devices.
\li QCanBusDevice provides an API for direct access to the CAN device.
\li QCanBusFrame defines a CAN frame that can be written and read from QCanBusDevice.
\endlist
\section1 CAN Bus Plugins
Multiple vendors provide CAN devices with varying APIs for access. The QtSerialBus module
supports the following sets of CAN bus plugins:
\table
\header
\li Vendor
\li Plugin (key)
\li Brief description
\row
\li CAN over Linux sockets
\li \l {Using SocketCAN Plugin}{SocketCAN} (\c socketcan)
\li CAN bus plugin using Linux sockets and open source drivers.
\row
\li CAN via SAE J2534 Pass-Thru
\li \l {Using PassThruCAN Plugin}{PassThruCAN} (\c passthrucan)
\li CAN bus plugin using the SAE J2534 Pass-Thru interface.
\row
\li SYS TEC electronic
\li \l {Using SystecCAN Plugin}{SystecCAN} (\c systeccan)
\li CAN bus backend using the SYS TEC CAN adapters.
\row
\li PEAK-System
\li \l {Using PeakCAN Plugin}{PeakCAN} (\c peakcan)
\li CAN bus plugin using the PEAK CAN adapters.
\row
\li MHS Elektronik
\li \l {Using TinyCAN Plugin}{TinyCAN} (\c tinycan)
\li CAN bus plugin using the MHS CAN adapters.
\row
\li Vector Informatik
\li \l {Using VectorCAN Plugin}{VectorCAN} (\c vectorcan)
\li CAN bus plugin using the Vector CAN adapters.
\row
\li Virtual CAN interface
\li \l {Using VirtualCAN Plugin}{VirtualCAN} (\c virtualcan)
\li CAN bus plugin using a virtual TCP/IP connection.
\endtable
\section1 Implementing a Custom CAN Plugin
If the plugins provided by Qt are not suitable for the required target platform,
a custom CAN bus plugin can be implemented. The implementation follows the standard
way of implementing Qt plug-ins. The custom plugin must be deployed
to \c {$QTDIR/plugins/canbus}.
Each plugin must define a key, which is used to load the plugin. This is done via a small json
file. For example, the socketcan plugin uses the following \c {plugin.json}:
\code
{
"Key": "socketcan"
}
\endcode
This key must be passed to \l {QCanBus::createDevice()} together with the interface name of
the CAN bus adapter. QCanBus loads and instantiates the plugin using the QCanBusFactoryV2
interface which each plugin must implement as central entry point. The interface acts as
a factory and its sole purpose is to return a \l QCanBusDevice instance. The above mentioned
interface name is passed on via the factory's \l QCanBusFactory::createDevice() method.
The following is the factory implementation of the \e socketcan plugin:
\snippet main.cpp SocketCanFactory
The next step is to provide an implementation of QCanBusDevice. At the very least, the
following pure virtual functions must be implemented:
\list
\li \l QCanBusDevice::open()
\li \l QCanBusDevice::close()
\li \l QCanBusDevice::writeFrame()
\li \l QCanBusDevice::interpretErrorFrame()
\endlist
The \l {QCanBusDevice::open()}{open()} and \l {QCanBusDevice::close()}{close()}
methods are used in conjunction with \l QCanBusDevice::connectDevice() and
\l QCanBusDevice::disconnectDevice() respectively. Check the
function documentation for implementation details.
\l QCanBusDevice::writeFrame() is responsible for sanity checks such as the validity
of the \l QCanBusFrame and that the device is still connected. Provided
that the checks passed, it writes the frame to the CAN bus. Upon success it emits
the \l QCanBusDevice::framesWritten() signal; otherwise \l QCanBusDevice::setError() is
called with an appropriate error message. This function may also be used to implement
an asynchronous write operation. It is the plugin implementors responsibility to emit
the appropriate signals at the appropriate time.
Last but not least, \l QCanBusDevice::interpretErrorFrame provides a convenient way
to translate the content of an CAN bus error frame to a human-readable error string.
*/
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