QCanSignalDescription Class | Qt Serial Bus | Qt 6.10.2
Description: The QCanSignalDescription class describes the rules to extract one value out of the CAN frame and represent it in an application-defined format.

- Qt 6.10
- Qt Serial Bus
- C++ Classes
- QCanSignalDescription
- Qt 6.10.2 Reference Documentation

# QCanSignalDescription Class

The QCanSignalDescription class describes the rules to extract one value out of the CAN frame and represent it in an application-defined format. More...

Header: | `#include <QCanSignalDescription>`
CMake: | `find_package(Qt6 REQUIRED COMPONENTS SerialBus)` `target_link_libraries(mytarget PRIVATE Qt6::SerialBus)`
qmake: | `QT += serialbus`
Since: | Qt 6.5
Status: | Preliminary

This class is under development and is subject to change.

- List of all members, including inherited members

## Public Types

`(since 6.5)` struct | MultiplexValueRange

## Public Functions

| QCanSignalDescription(QCanSignalDescription &&other)
| ~QCanSignalDescription()
Q_DECL_IMPORT | addMultiplexSignal(const int &name, const int &value)
Q_DECL_IMPORT | clearMultiplexSignals()
Q_DECL_IMPORT | factor() const
Q_DECL_IMPORT | maximum() const
Q_DECL_IMPORT | minimum() const
Q_DECL_IMPORT | offset() const
Q_DECL_IMPORT | scaling() const
Q_DECL_IMPORT | setBitLength(int length)
Q_DECL_IMPORT | setComment(const int &text)
Q_DECL_IMPORT | setDataEndian(int endian)
Q_DECL_IMPORT | setDataFormat(QtCanBus::DataFormat format)
Q_DECL_IMPORT | setDataSource(QtCanBus::DataSource source)
Q_DECL_IMPORT | setFactor(double factor)
Q_DECL_IMPORT | setMultiplexSignals(const int &multiplexorSignals)
Q_DECL_IMPORT | setMultiplexState(QtCanBus::MultiplexState state)
Q_DECL_IMPORT | setName(const int &name)
Q_DECL_IMPORT | setOffset(double offset)
Q_DECL_IMPORT | setPhysicalUnit(const int &unit)
Q_DECL_IMPORT | setRange(double minimum, double maximum)
Q_DECL_IMPORT | setReceiver(const int &receiver)
Q_DECL_IMPORT | setScaling(double scaling)
Q_DECL_IMPORT | setStartBit(int bit)
QCanSignalDescription & | operator=(QCanSignalDescription &&other)

## Detailed Description

The QCanSignalDescription class can be used to provide a signal description and later use it to decode a received QCanBusFrame or encode the input data into a QCanBusFrame that can be sent to the receiver.

#### General Description

Each CAN frame can contain multiple values. The rules to extract the values from a CAN frame include the following:

- Data source (frame ID or payload).
- Data endianness. See Data Endianness Processing section for more details.
- Data format.
- Start bit position.
- Data length in bits.
- Multiplexing options.

Start bit position is specified relative to the selected data source. The bits are counted starting from the LSB.

Once the data is extracted, it might require conversion to an application-defined format. The following parameters can be used for that:

- Various parameters for converting the extracted value to a physical value (factor, offset, scale).
- Expected data range.
- Data units.

The QCanSignalDescription class provides methods to control all those parameters.

#### Data Endianness Processing

Little endian and big endian data is encoded differently. For big endian values, start bit positions are given for the most significant bit. For little endian values, the start position is that of the least significant bit.

Let's consider two examples. In both examples we will encode two 12-bit values in the 3-byte payload.

##### Little Endian

For the little endian case the data layout can be represented by the following image:

Here the columns represent bit numbers, and the rows represent byte numbers. `LSB` marks the first (least significant) bit of the value, and `MSB` marks the last (most significant) bit of the value. The blue color marks the first value, and the orange color marks the second value.

The information about these values will be encoded in QCanSignalDescription in the following way:

     QCanSignalDescription signal1;
     signal1.setDataEndian(QSysInfo::Endian::LittleEndian);
     signal1.setStartBit(0);
     signal1.setBitLength(12);
     // other parameters for signal1

     QCanSignalDescription signal2;
     signal2.setDataEndian(QSysInfo::Endian::LittleEndian);
     signal2.setStartBit(12);
     signal2.setBitLength(12);
     // other parameters for signal2

##### Big Endian

The following image represents the value layout for the big endian case:

The values can be represented in QCanSignalDescription in the following way:

     QCanSignalDescription signal1;
     signal1.setDataEndian(QSysInfo::Endian::BigEndian);
     signal1.setStartBit(7);
     signal1.setBitLength(12);
     // other parameters for signal1

     QCanSignalDescription signal2;
     signal2.setDataEndian(QSysInfo::Endian::BigEndian);
     signal2.setStartBit(11);
     signal2.setBitLength(12);
     // other parameters for signal2

Note how the start bits are different from the little endian case. Also the values are aligned differently.

#### Multiplexed Signals Explained

There are two common ways to encode the data in the CAN payload:

- Each range of bits always represents the same signal. For example, `Bytes 0-1` in a payload can represent an engine speed (in rpm), and `Bytes 2-3` can represent the vehicle speed (in km/h).
- The same range of bits can represent different data, depending on the values of some other bits in the payload. For example, if `Byte 0` has the value `0`, the `Bytes 1-2` represent an engine speed (in rpm), and if `Byte 0` has the value `1`, the same `Bytes 1-2` represent a vehicle speed (in km/h).

The second case uses signal multiplexing. In the provided example we will have three signals. The first signal represents the value of `Byte 0` and acts like a multiplexor signal. The other two signals represent an engine speed and a vehicle speed respectively, but only one of them can be extracted from the CAN payload at a time. Which signal should be extracted is defined by the value of the multiplexor signal.

In more complicated cases the payload can have multiple multiplexor signals. In such cases the signal can be extracted from the payload only when all multiplexors contain the expected values.

#### Value Conversions

In many cases the signals transferred over CAN bus cannot hold the full range of the physical values that they represent. To overcome these limitations, the physical values are converted to a smaller range before transmission, and can be restored on the receiving end.

The following formulas are used to convert between the physical value and the signal's value:

     physicalValue = scaling * (signalValue * factor + offset);
     signalValue = (physicalValue / scaling - offset) / factor;

The factor and scaling parameters cannot be equal to `0`.

If any of the parameters equals to qQNaN(), it is not used during the conversion. If all of the parameters are equal to qQNaN() (which is the default), the conversion is not performed.

## Member Function Documentation

### `[constexpr noexcept]` QCanSignalDescription::QCanSignalDescription(QCanSignalDescription &&other)

Creates a signal description by moving from other.

Note: The moved-from QCanSignalDescription object can only be destroyed or assigned to. The effect of calling other functions than the destructor or one of the assignment operators is undefined.

### `[constexpr noexcept]` QCanSignalDescription::~QCanSignalDescription()

Destroys this signal description.

### Q_DECL_IMPORT QCanSignalDescription::addMultiplexSignal(const int &name, const int &value)

This is a convenience overload for the case when the multiplexor signal is expected to have only one specific value, not a range of values.

The name parameter contains the name of the multiplexor signal, and the value parameter contains the desired value.

If this signal already has desired value ranges for the multiplexor signal name, the ranges are overwritten.

See also multiplexState(), multiplexSignals(), clearMultiplexSignals(), and setMultiplexSignals().

### Q_DECL_IMPORT QCanSignalDescription::clearMultiplexSignals()

Removes all multiplexor signals for this signal.

See also multiplexSignals(), setMultiplexSignals(), and addMultiplexSignal().

### Q_DECL_IMPORT QCanSignalDescription::factor() const

Returns the factor that is used to convert the signal's value to a physical value and back.

By default the function returns qQNaN(), which means that a factor is not used.

The Value Conversions section explains how this parameter is used.

See also setFactor(), offset(), and scaling().

### Q_DECL_IMPORT QCanSignalDescription::maximum() const

Returns the maximum supported value for the signal.

By default the function returns qQNaN(), which means that there is no maximum value.

See also setRange() and minimum().

### Q_DECL_IMPORT QCanSignalDescription::minimum() const

Returns the minimum supported value for the signal.

By default the function returns qQNaN(), which means that there is no minimum value.

See also setRange() and maximum().

### Q_DECL_IMPORT QCanSignalDescription::offset() const

Returns the offset that is used to convert the signal's value to a physical value and back.

By default the function returns qQNaN(), which means that an offset is not used.

The Value Conversions section explains how this parameter is used.

See also setOffset(), factor(), and scaling().

### Q_DECL_IMPORT QCanSignalDescription::scaling() const

Returns the scaling that is used to convert the signal's value to a physical value and back.

By default the function returns qQNaN(), which means that scaling is not used.

The Value Conversions section explains how this parameter is used.

See also setScaling(), offset(), and factor().

### Q_DECL_IMPORT QCanSignalDescription::setBitLength(int length)

Sets the bit length of the signal's value to length.

See also bitLength(), startBit(), and setStartBit().

### Q_DECL_IMPORT QCanSignalDescription::setComment(const int &text)

Sets the comment for the signal to text.

This parameter is introduced only for extra description. It's not used during signal processing.

See also comment().

### Q_DECL_IMPORT QCanSignalDescription::setDataEndian(int endian)

Sets the data endian of the signal's value to endian.

See also dataEndian() and QSysInfo::Endian.

### Q_DECL_IMPORT QCanSignalDescription::setDataFormat(QtCanBus::DataFormat format)

Sets the data format of the signal's value to format.

See also dataFormat() and QtCanBus::DataFormat.

### Q_DECL_IMPORT QCanSignalDescription::setDataSource(QtCanBus::DataSource source)

Sets the data source of the signal's value to source.

See also dataSource() and QtCanBus::DataSource.

### Q_DECL_IMPORT QCanSignalDescription::setFactor(double factor)

Sets the factor that is used to convert the signal's value to a physical value and back to factor.

Pass qQNaN() to this method to skip this parameter during the conversion.

The factor cannot be 0. An attempt to set a zero factor is equivalent to setting it to qQNaN().

The Value Conversions section explains how this parameter is used.

See also factor(), setOffset(), and setScaling().

### Q_DECL_IMPORT QCanSignalDescription::setMultiplexSignals(const int &multiplexorSignals)

Sets the multiplexor signals for this signal to multiplexorSignals.

The multiplexorSignals hash must contain signal names as keys and respective desired value ranges as values.

See also multiplexState(), multiplexSignals(), clearMultiplexSignals(), and addMultiplexSignal().

### Q_DECL_IMPORT QCanSignalDescription::setMultiplexState(QtCanBus::MultiplexState state)

Sets the multiplex state of the signal to state.

See the Multiplexed Signals Explained section for more details on multiplexed signals.

See also multiplexState() and QtCanBus::MultiplexState.

### Q_DECL_IMPORT QCanSignalDescription::setName(const int &name)

Sets the name of the signal to name.

The signal's name must be unique within a CAN message.

See also name().

### Q_DECL_IMPORT QCanSignalDescription::setOffset(double offset)

Sets the offset that is used to convert the signal's value to a physical value and back to offset.

Pass qQNaN() to this method to skip this parameter during the conversion.

The Value Conversions section explains how this parameter is used.

See also offset(), setFactor(), and setScaling().

### Q_DECL_IMPORT QCanSignalDescription::setPhysicalUnit(const int &unit)

Sets the physical unit (e.g. km/h) of the signal's value.

This parameter is introduced only for extra description. It's not used during signal processing.

See also physicalUnit().

### Q_DECL_IMPORT QCanSignalDescription::setRange(double minimum, double maximum)

Sets the minimum and maximum for the signal's value.

Setting one or both of the parameters to qQNaN() means that the corresponding limit will not be used.

See also minimum() and maximum().

### Q_DECL_IMPORT QCanSignalDescription::setReceiver(const int &receiver)

Sets the receiver node for this signal.

This parameter is introduced only for extra description. It's not used during signal processing.

See also receiver().

### Q_DECL_IMPORT QCanSignalDescription::setScaling(double scaling)

Sets the scaling that is used to convert the signal's value to a physical value and back to scaling.

Pass qQNaN() to this method to skip this parameter during the conversion.

The scaling cannot be 0. An attempt to set zero scaling is equivalent to setting it to qQNaN().

The Value Conversions section explains how this parameter is used.

See also scaling(), setOffset(), and setFactor().

### Q_DECL_IMPORT QCanSignalDescription::setStartBit(int bit)

Sets the start bit of the signal's value in the dataSource() to bit.

See also startBit(), bitLength(), and setBitLength().

### `[noexcept default]` QCanSignalDescription &QCanSignalDescription::operator=(QCanSignalDescription &&other)

Move-assigns the values from other to this signal description.

Note: The moved-from QCanSignalDescription object can only be destroyed or assigned to. The effect of calling other functions than the destructor or one of the assignment operators is undefined.