[Solved] QtSerialPort and Threads

RodriguesCunha

Hi, Thanks kuzulis.

I thought of using threads and blocking approach because if I'm processing received data i can't do anything else in my gui.

As i mentioned i need to receive data, update gui, do some calculations and write back to pic. And i think that if i use async approach in guithread my app will be most of the time processing reception. Also i will receive data from another serial device.

kuzulis

UPD:

bq. I need to receive a data array, from a PIC18F, for example: 0 | 1 | 3 | 121 | 50 | 99 other is 0 | 2 | 2 | 10 | 150

bq. to detect the start i use 0, then message identifier (1 or 2), next the number of data bytes and finally the data bytes (data will change).

I don't understand that to you is unclear?

@

...
enum ParserState { WaitForStart, WaitForMsgId, WaitForData, Done };

static ParserState currentParserState = WaitForStart; // start synchronization
...

...
connect(port, SIGNAL(readyRead()), this, SLOT(onParseInputStream()));
...

SerialPortHandlingLayer::onParseInputStream()
{
while (port->bytesAvailable() > 0) {
switch (currentParserState) {
case WaitForStart:
char c = 0;
if (port->peek(&c, 1) > 0 && (c == 0)) {
currentParserState = WaitForMsgId;
} else {
// read wrong char to dummy, skip it
port->read(&c, 1);
// stay on WaitForStart
}
break;

    case WaitForMsgId: 
        QByteArray ba = port->peek(2);
        if (ba.at(1) == 1 ||ba.at(1) == 2) {
            currentParserState = WaitForData;
        } else {
            // read wrong char to dummy, skip it
            port->read(&c, 1);
            // transition to WaitForStart
            currentParserState = WaitForStart;
        }
        break;

    case WaitForData:
        // parse next length field from data
        QByteArray ba = port->peek(3);
        int msgLength = ba.at(2);
        if (msgLength <= port->bytesAvailable() - 2) {
            // all complete data is available
            // skip start, id, length field
            QByteArray dummy = port->read(3);
            // read complete data
            QByteArray data =  port->read(msgLength);

            emit port->completeData(data);
        } else {
            // not all data is available, wait for next readyRead()
            return;
        }
         break;
    }
}

}

@

RodriguesCunha

This part i already have working.
The problem is that while i'm doing reception i can't do anything else.

kuzulis

You can do the calculations (parse or something else) in a separate thread (e.g. using QtConcurrent) and pass the result of the calculations through the signal to the QtSerialPort back. So, I not see a problem.

SGaist

Then don't block: read what is available on the port in a QByteArray and once the QByteArray has the correct size, do your computation.

Between two readyRead, your GUI will be responsive.

RodriguesCunha

Hi, I will try your approach, but i will need to receive data from another serialport. How can i do this? Because if i'm processing the readyRead() of the first, my app can't process the readyRead() of the second...
That's why i first thought about threads..

kuzulis

Sorry? You give us all new and new surprises? :)

bq. Hi, I will try your approach, but i will need to receive data from another serialport. How can i do this?

This:
@
QSerialPort *port1 = new QSerialPort;
QSerialPort *port2 = new QSerialPort;

connect(port1, SIGNAL(readyRead()),
this, SLOT(onReadyReadFromPort1()));

connect(port2, SIGNAL(readyRead()),
this, SLOT(onReadyReadFromPort2()));

port1->setPortName("COM1");
port2->setPortName("COM125");

...
...
...
@

does not work? :)

RodriguesCunha

I already had mentioned it in a previous post.

I thought of doing like you say, but my question is: if both signals happen at same time, won't my program freeze? It will only process one or the other, or so i think... Or can 2 slots be processed at the same time?

kuzulis

bq. if both signals happen at same time, won’t my program freeze?

It depends on the code that you implement in the handler of each slot.

bq. Or can 2 slots be processed at the same time?

Any slot/signal is executed in turn in a context of the current thread. Only one slot it is possible to process at the same time. Signals can't come at the same time, all (signals and slots) is processing from Qt event-loop queue (as a whole).

Please, read documentation on Qt as a whole...

RodriguesCunha

Ok, like i thought.
That's why i first thought on using Threads...
So that each serialport could only deal with one port.