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/****************************************************************************
**
** Copyright (C) 2015 The Qt Company Ltd.
** Contact: http://www.qt.io/licensing/
**
** This file is part of the documentation of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:FDL$
** Commercial License Usage
** Licensees holding valid commercial Qt licenses may use this file in
** accordance with the commercial license agreement provided with the
** Software or, alternatively, in accordance with the terms contained in
** a written agreement between you and The Qt Company. For licensing terms
** and conditions see http://www.qt.io/terms-conditions. For further
** information use the contact form at http://www.qt.io/contact-us.
**
** GNU Free Documentation License Usage
** Alternatively, this file may be used under the terms of the GNU Free
** Documentation License version 1.3 as published by the Free Software
** Foundation and appearing in the file included in the packaging of
** this file. Please review the following information to ensure
** the GNU Free Documentation License version 1.3 requirements
** will be met: http://www.gnu.org/copyleft/fdl.html.
** $QT_END_LICENSE$
**
****************************************************************************/
/*!
\page qtserialbus-socketcan-overview.html
\title Using SocketCAN Plugin
\brief Overview of how to use the SocketCAN plugin.
The SocketCAN plugin encapsulates the Linux sockets API for accessing the CAN devices.
This API is a set of open source CAN drivers and a networking stack contributed by
Volkswagen Research to the Linux kernel.
This plugin requires a Linux Kernel with SocketCAN support and SocketCAN device
drivers for the used CAN hardware.
\section1 SocketCAN usage
To list all (including unconfigured) network interfaces, the command
\c{ifconfig -a} can be used.
To use SocketCAN, the corresponding Linux Kernel modules must be loaded
and the network interface must be configured.
\section2 Setting up real CAN hardware
This section assumes, that the device driver is already loaded
(most likely automatically when connecting the CAN hardware).
\section3 Default settings
To set the device can0 to a bitrate of 250 kBit/s:
\code
sudo ip link set up can0 type can bitrate 250000
\endcode
To automatically recover from "bus off" errors after 100 milliseconds,
the following command can be used:
\code
sudo ip link set up can0 type can bitrate 250000 restart-ms 100
\endcode
\section3 CAN FD settings
To set the device can0 to an arbitration bitrate of 500 kBit/s and a data
bitrate of 4 MBit/s (for frames with bitrate switch flag):
\code
sudo ip link set can0 up type can bitrate 500000 dbitrate 4000000 fd on
\endcode
\section2 Setting up a virtual CAN bus
\note For CAN FD usage, the MTU (Maximum Transmission Unit) has to be set
to 72 byte.
\code
sudo modprobe vcan
sudo ip link add dev vcan0 type vcan
sudo ip link set up vcan0 mtu 72
\endcode
The command line test programs used in the following are from
the \l{https://github.com/linux-can/can-utils}{can-utils} package:
\code
# Display received CAN messages with absolute timestamps and flags
candump -ta -x vcan0
# Send a CAN FD message with flags BRS and EFI set
cansend vcan0 123##3112233445566778899aabbccddeeff
# Generate random CAN messages
cangen vcan0
\endcode
\section1 Creating CAN Bus Devices
At first it is necessary to check that QCanBus provides the desired plugin:
\code
if (QCanBus::instance()->plugins().contains(QStringLiteral("socketcan"))) {
// plugin available
}
\endcode
Where \e socketcan is the plugin name.
Next, a connection to a specific interface can be established:
\code
QCanBusDevice *device = QCanBus::instance()->createDevice(
QStringLiteral("socketcan"), QStringLiteral("can0"));
device->connectDevice();
\endcode
Where \e can0 is the active CAN interface name. CAN interfaces act like regular
network interfaces on Linux systems and can be discovered using \c ifconfig.
The device is now open for writing and reading CAN frames:
\code
QCanBusFrame frame;
frame.setFrameId(8);
QByteArray payload("A36E");
frame.setPayload(payload);
device->writeFrame(frame);
\endcode
The reading can be done using the \l {QCanBusDevice::}{readFrame()} method. The
\l {QCanBusDevice::}{framesReceived()} signal is emitted when at least one new frame
is available for reading:
\code
QCanBusFrame frame = device->readFrame();
\endcode
SocketCAN supports the following configurations that can be controlled through
\l {QCanBusDevice::}{setConfigurationParameter()}:
\table
\header
\li Configuration parameter key
\li Description
\row
\li QCanBusDevice::LoopbackKey
\li To meet the multiple-user needs, the local loopback is enabled by default.
This means, whenever a CAN frame is transmitted on the CAN bus, a local
echo of this frame is sent to all applications connected to this CAN device.
If this option is enabled, the therefore received frames are marked with
QCanBusFrame::hasLocalEcho()
\row
\li QCanBusDevice::ReceiveOwnKey
\li The reception of the CAN frames on the same socket that was sending the CAN frame
is disabled by default. When enabling this option, all CAN frames sent to the CAN
bus immediately appear in the receive buffer. This can be used to check if sending
was successful. If this option is enabled, the therefore received frames are marked
with QCanBusFrame::hasLocalEcho()
\row
\li QCanBusDevice::ErrorFilterKey
\li A CAN interface driver can generate so called \e {Error Message Frames} that can
optionally be passed to the user application in the same way as other CAN frames.
The possible errors are divided into different error classes that may be filtered
using the appropriate error mask. The values for the error mask are defined in
\c {linux/can/error.h}.
\row
\li QCanBusDevice::RawFilterKey
\li This configuration can contain multiple filters of type \l QCanBusDevice::Filter.
By default, the connection is configured to accept any CAN bus message.
\row
\li QCanBusDevice::BitRateKey
\li This configuration is not supported by the socketcan plugin. However
it is possible to set the rate when configuring the CAN network interface using
the \c {ip link} command.
\row
\li QCanBusDevice::CanFdKey
\li This configuration option determines whether CANFD frames may be sent or received.
By default, this option is disabled. It controls the CAN_RAW_FD_FRAMES
option of the CAN socket.
\row
\li QCanBusDevice::DataBitRateKey
\li This configuration is not supported by the socketcan plugin. However
it is possible to set the data rate when configuring the CAN network interface
using the \c {ip link} command.
\endtable
For example:
\snippet snippetmain.cpp SocketCan Filter Example
Extended frame format and flexible data-rate are supported in SocketCAN.
*/
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