Now the playback window is capable of vastly quicker sending of frames.

Use the burst setting and crank it up. Set the time interval to around 2ms and the burst to 6 and you'll be slinging frames like crazy.

serialworker.cpp

@@ -70,11 +70,11 @@ void SerialWorker::setSerialPort(QSerialPortInfo *port)
     serial = new QSerialPort(*port);    
 
     qDebug() << "Serial port name is " << port->portName();
-    serial->setBaudRate(serial->Baud115200);
+    serial->setBaudRate(10000000); //more speed! probably does nothing for USB serial
     serial->setDataBits(serial->Data8);
-    serial->setFlowControl(serial->HardwareControl);
+    serial->setFlowControl(serial->HardwareControl); //this is important though
     serial->open(QIODevice::ReadWrite);
-    serial->setDataTerminalReady(true);
+    serial->setDataTerminalReady(true); //you do need to set these or the fan gets dirty
     serial->setRequestToSend(true);
     QByteArray output;
     output.append(0xE7); //this puts the device into binary comm mode
@@ -85,6 +85,8 @@ void SerialWorker::setSerialPort(QSerialPortInfo *port)
     output.append(0x07); //request device information
     output.append(0xF1);
     output.append(0x08); //setting singlewire mode
+    output.append(0xF1); //yet another command
+    output.append(0x09); //comm validation command
     if (settings.value("Main/SingleWireMode", false).toBool())
     {
         output.append(0x10); //signal that we do want single wire mode
@@ -122,6 +124,7 @@ void SerialWorker::connectionTimeout()
         //then emit the the failure signal and see if anyone cares
         qDebug() << "Failed to connect to GVRET at that com port";
         ticker->stop();
+        closeSerialPort(); //make sure it's properly closed anyway
         emit connectionFailure();
     }
 }
@@ -171,6 +174,14 @@ void SerialWorker::sendFrame(const CANFrame *frame, int bus = 0)
     serial->write(buffer);
 }
 
+//a simple way for another thread to pass us a bunch of frames to send.
+//Don't get carried away here. The GVRET firmware only has finite
+//buffers and besides, the other end will get buried in traffic.
+void SerialWorker::sendFrameBatch(const QList<CANFrame> *frames)
+{
+    for (int i = 0; i < frames->length(); i++) sendFrame(&frames->at(i), frames->at(i).bus);
+}
+
 void SerialWorker::updateBaudRates(int Speed1, int Speed2)
 {
     QByteArray buffer;