QCanBusDevice Class | Qt Serial Bus 5.6

Qt Documentation (Technology Preview) | Qt Serial Bus | C++ Classes | QCanBusDevice

Qt 5.6.2 Reference Documentation

# QCanBusDevice Class

The QCanBusDevice class is the interface class for CAN bus. More...

Header: | #include <QCanBusDevice>
qmake: | QT += serialbus
Since: | Qt 5.6
Inherits: | QObject

- List of all members, including inherited members

## Public Types

class | Filter
enum | CanBusDeviceState { UnconnectedState, ConnectingState, ConnectedState, ClosingState }
enum | CanBusError { NoError, ReadError, WriteError, ConnectionError, ConfigurationError, UnknownError }
enum | ConfigurationKey { RawFilterKey, ErrorFilterKey, LoopbackKey, ReceiveOwnKey, ..., UserKey }

## Public Functions

| QCanBusDevice(QObject *parent = nullptr)
QVector<int> | configurationKeys() const
QVariant | configurationParameter(int key) const
bool | connectDevice()
void | disconnectDevice()
CanBusError | error() const
QString | errorString() const
qint64 | framesAvailable() const
qint64 | framesToWrite() const
virtual QString | interpretErrorFrame(const QCanBusFrame &frame) = 0
QCanBusFrame | readFrame()
virtual void | setConfigurationParameter(int key, const QVariant &value)
CanBusDeviceState | state() const
virtual bool | writeFrame(const QCanBusFrame &frame) = 0

- 31 public functions inherited from QObject

## Signals

void | errorOccurred(QCanBusDevice::CanBusError error)
void | framesReceived()
void | framesWritten(qint64 framesCount)
void | stateChanged(QCanBusDevice::CanBusDeviceState state)

- 2 signals inherited from QObject

## Protected Functions

virtual void | close() = 0
QCanBusFrame | dequeueOutgoingFrame()
void | enqueueOutgoingFrame(const QCanBusFrame &newFrame)
void | enqueueReceivedFrames(const QVector<QCanBusFrame> &newFrames)
bool | hasOutgoingFrames() const
virtual bool | open() = 0
void | setError(const QString &errorText, QCanBusDevice::CanBusError errorId)
void | setState(QCanBusDevice::CanBusDeviceState newState)

- 9 protected functions inherited from QObject

### Additional Inherited Members

- 1 property inherited from QObject
- 1 public slot inherited from QObject
- 1 public variable inherited from QObject
- 10 static public members inherited from QObject
- 2 protected variables inherited from QObject

## Detailed Description

The QCanBusDevice class is the interface class for CAN bus.

QCanBusDevice communicates with a CAN backend providing users with a convenient API. The CAN backend must be specified during the object creation.

## Member Type Documentation

### enum QCanBusDevice::CanBusDeviceState

This enum describes all possible device states.

Constant | Value | Description
--- | --- | ---
`QCanBusDevice::UnconnectedState` | `0` | The device is disconnected.
`QCanBusDevice::ConnectingState` | `1` | The device is being connected.
`QCanBusDevice::ConnectedState` | `2` | The device is connected to the CAN bus.
`QCanBusDevice::ClosingState` | `3` | The device is being closed.

### enum QCanBusDevice::CanBusError

This enum describes all the possible error conditions.

Constant | Value | Description
--- | --- | ---
`QCanBusDevice::NoError` | `0` | No errors have occurred.
`QCanBusDevice::ReadError` | `1` | An error occurred during a read operation.
`QCanBusDevice::WriteError` | `2` | An error occurred during a write operation.
`QCanBusDevice::ConnectionError` | `3` | An error occurred when attempting to open the backend.
`QCanBusDevice::ConfigurationError` | `4` | An error occurred when attempting to set a configuration parameter.
`QCanBusDevice::UnknownError` | `5` | An unknown error occurred.

### enum QCanBusDevice::ConfigurationKey

This enum describes the possible configuration options for the CAN bus connection.

Constant | Value | Description
--- | --- | ---
`QCanBusDevice::RawFilterKey` | `0` | This configuration determines the type of CAN bus frames that the current device accepts. The expected value is `QList<QCanBusDevice::Filter>`. Passing an empty list clears all previously set filters including default filters. For more details see QCanBusDevice::Filter.
`QCanBusDevice::ErrorFilterKey` | `1` | This key defines the type of error that should be forwarded via the current connection. The associated value should be of type QCanBusFrame::FrameErrors.
`QCanBusDevice::LoopbackKey` | `2` | This key defines whether the CAN bus device should operate in loopback mode. The expected value for this key is `bool`.
`QCanBusDevice::ReceiveOwnKey` | `3` | This key defines whether this CAN device can send messages. The expected value for this key is `bool`.
`QCanBusDevice::BitRateKey` | `4` | This key defines the bitrate in bits per second.
`QCanBusDevice::CanFdKey` | `5` | This key defines whether sending and receiving of CAN FD frames should be enabled. The expected value for this key is `bool`.
`QCanBusDevice::UserKey` | `30` | This key defines the range where custom keys start. It's most common purpose is to permit platform-specific configuration options.

See also configurationParameter().

## Member Function Documentation

### QCanBusDevice::QCanBusDevice(QObject *parent = nullptr)

Constructs a serial bus device with the specified parent.

### `[pure virtual protected]` void QCanBusDevice::close()

This function is responsible for closing the CAN bus connection. The implementation must ensure that the instance's state() is set to QCanBusDevice::UnconnectedState.

This function's most important task is to close the socket to the CAN device and to call QCanBusDevice::setState().

See also disconnectDevice().

### QVector<int> QCanBusDevice::configurationKeys() const

Returns the list of keys used by the CAN bus connection.

The the meaning of the keys is equivalent to ConfigurationKey. If a key is not explicitly mentioned the platform's default setting for the relevant key is used.

### QVariant QCanBusDevice::configurationParameter(int key) const

Returns the current value assigned to the ConfigurationKey key; otherwise an invalid QVariant.

See also setConfigurationParameter() and configurationKeys().

### bool QCanBusDevice::connectDevice()

Connects the device to the CAN bus. Returns `true` on success; otherwise `false`.

This function calls open() as part of its implementation.

### `[protected]` QCanBusFrame QCanBusDevice::dequeueOutgoingFrame()

Returns the next QCanBusFrame from the internal list of outgoing frames; otherwise returns an invalid QCanBusFrame. The returned frame is removed from the internal list.

### void QCanBusDevice::disconnectDevice()

Disconnects the device from the CAN bus.

This function calls close() as part of its implementation.

### `[protected]` void QCanBusDevice::enqueueOutgoingFrame(const QCanBusFrame &newFrame)

Appends newFrame to the internal list of outgoing frames which can be accessed by writeFrame().

Subclasses must call this function when they write a new frame.

### `[protected]` void QCanBusDevice::enqueueReceivedFrames(const QVector<QCanBusFrame> &newFrames)

Appends newFrames to the internal list of frames which can be accessed using readFrame() and emits the framesReceived() signal.

Subclasses must call this function when they receive frames.

### CanBusError QCanBusDevice::error() const

Returns the last error that has occurred. The error value is always set to last error that occurred and it is never reset.

See also setError() and errorString().

### `[signal]` void QCanBusDevice::errorOccurred(QCanBusDevice::CanBusError error)

This signal is emitted when an error of the type error occurs.

### QString QCanBusDevice::errorString() const

Returns a human-readable description of the last device error that occurred.

See also error().

### qint64 QCanBusDevice::framesAvailable() const

Returns the number of available frames. If no frames are available, this function returns 0.

See also readFrame().

### `[signal]` void QCanBusDevice::framesReceived()

This signal is emitted when one or more frames have been received. The frames should be read using readFrame() and framesAvailable().

### qint64 QCanBusDevice::framesToWrite() const

Returns the number of frames waiting to be written.

See also writeFrame().

### `[signal]` void QCanBusDevice::framesWritten(qint64 framesCount)

This signal is emitted every time a payload of frames has been written to the CAN bus. The framesCount argument is set to the number of frames that were written in this payload.

### `[protected]` bool QCanBusDevice::hasOutgoingFrames() const

Returns `true` if the internal list of outgoing frames is not empty; otherwise returns `false`.

### `[pure virtual]` QString QCanBusDevice::interpretErrorFrame(const QCanBusFrame &frame)

Interprets frame as error frame and returns a human readable description of the error.

If frame is not an error frame, the returned string is empty.

### `[pure virtual protected]` bool QCanBusDevice::open()

This function is called by connectDevice(). Subclasses must provide an implementation which returns `true` if the CAN bus connection could be established; otherwise `false`. The QCanBusDevice implementation ensures upon entry of this function that the device's state() is set to QCanBusDevice::ConnectingState already.

The implementation must ensure that upon success the instance's state() is set to QCanBusDevice::ConnectedState; otherwise QCanBusDevice::UnconnectedState. setState() must be used to set the new device state.

The custom implementation is responsible for opening the socket, instanciation of a potentially required QSocketNotifier and the application of custom and default QCanBusDevice::configurationParameter().

See also connectDevice().

### QCanBusFrame QCanBusDevice::readFrame()

Returns the next QCanBusFrame from the queue; otherwise returns an empty QCanBusFrame. The returned frame is removed from the queue.

The queue operates according to the FIFO principle.

See also framesAvailable().

### `[virtual]` void QCanBusDevice::setConfigurationParameter(int key, const QVariant &value)

Sets the configuration parameter key for the CAN bus connection to value. The potential keys are represented by ConfigurationKey.

A parameter can be unset by setting an invalid QVariant. Unsetting a parameter implies that the configuration is reset to its default setting.

Note: In most cases, configuration changes only take effect after a reconnect.

See also configurationParameter().

### `[protected]` void QCanBusDevice::setError(const QString &errorText, QCanBusDevice::CanBusError errorId)

Sets the human readable description of the last device error to errorText. errorId categorizes the type of error.

CAN bus implementations must use this function to update the device's error state.

See also error() and errorOccurred().

### `[protected]` void QCanBusDevice::setState(QCanBusDevice::CanBusDeviceState newState)

Sets the state of the device to newState. CAN bus implementations must use this function to update the device state.

See also state().

### CanBusDeviceState QCanBusDevice::state() const

Returns the current state of the device.

See also setState() and stateChanged().

### `[signal]` void QCanBusDevice::stateChanged(QCanBusDevice::CanBusDeviceState state)

This signal is emitted every time the state of the device changes. The new state is represented by state.

See also setState() and state().

### `[pure virtual]` bool QCanBusDevice::writeFrame(const QCanBusFrame &frame)

Writes frame to the CAN bus and returns `true` on success; otherwise `false`.

On some platforms, the frame may be put into a queue and the return value may only indicate a successful insertion into the queue. The actual frame will be send later on. Therefore the framesWritten() signal is the final confirmation that the frame has been handed off to the transport layer. If an error occurs the errorOccurred() is emitted.

As per CAN bus specification, frames of type remote transfer request (RTR) do not have a payload but require a size larger than zero. This size indicates the expected response payload length from the remote party. Therefore when sending a RTR frame using this function it may still be required to set an arbitrary payload on frame. The length of the arbitrary payload is what is set as size expectation for the RTR frame.

See also QCanBusFrame::setPayload().