Tutorial: Writing a Multiplexer Plug-in

Multiplexers That Use Multiple Serial Ports

Some GSM modules use multiple serial ports, one per channel. The QMultiPortMultiplexer class can be used to support such modules. As an example, consider a module with the following serial ports:

• /dev/mux0 Primary AT command channel.
• /dev/mux1 Secondary AT command channel.
• /dev/mux2 GPRS data channel.

To support such a module, first set QTOPIA_PHONE_DEVICE to /dev/mux0 in the custom.h file for the platform. Then the detect() and create() methods would be implemented as follows:

    class MultiPortMultiplexerPlugin : public QSerialIODeviceMultiplexerPlugin
    {
        Q_OBJECT
    public:
        MultiPortMultiplexerPlugin( QObject *parent = 0 )
            : QSerialIODeviceMultiplexerPlugin( parent ) {}

        bool detect( QSerialIODevice *device );
        QSerialIODeviceMultiplexer *create( QSerialIODevice *device );
    };

    bool MultiPortMultiplexerPlugin::detect( QSerialIODevice * )
    {
        return true;
    }

    QSerialIODeviceMultiplexer *MultiPortMultiplexerPlugin::create( QSerialIODevice *device )
    {
        // The primary AT command device, /dev/mux0, is configured
        // in the custom.h file as QTOPIA_PHONE_DEVICE and then passed
        // down to us in the "device" parameter.
        QMultiPortMultiplexer *mux = new QMultiPortMultiplexer( device );

        // Add the secondary channel.
        QSerialPort *secondary = QSerialPort::create( "/dev/mux1" );
        mux->addChannel( "secondary", secondary );

        // Add the data channel.
        QSerialPort *data = QSerialPort::create( "/dev/mux2" );
        mux->addChannel( "data", data );

        // Add the data setup channel, which is the same as "data".
        mux->addChannel( "datasetup", data );
        return mux;
    }

    QTOPIA_EXPORT_PLUGIN( MultiPortMultiplexerPlugin )

The first parameter to QMultiPortMultiplexer::addChannel() is the name of the channel that is being set. It may be one of the following standard names:

• primary - primary AT command channel
• secondary - secondary AT command channel
• data GPRS - data channel
• datasetup - channel that receives GPRS setup commands.

Other channel names are possible. Refer to the documentation for QSerialIODeviceMultiplexer for further details.

Some modules only have one AT command channel, not two. For such modules, both primary and secondary should be set to the same value:

    QMultiPortMultiplexer *mux = new QMultiPortMultiplexer( device );
    mux->addChannel( "secondary", device );

Some modules require that GPRS setup commands such as AT+CGDCONT and ATD must be sent on the primary AT command channel, not the data channel. For such modules, datasetup should be set to the same value as primary.