Why the Qt(4.8) serial port readind data from device in 2 part?

MhM93

Hi
this is my code : (I used qextserialport)

SerialPort::SerialPort(QString port)
{
    sp=new QextSerialPort;
    sp->setPortName(port);
    /*port->setBaudRate(BAUD9600);
    port->setFlowControl(FLOW_OFF);
    port->setParity(PAR_NONE);
    port->setDataBits(DATA_8);
    port->setStopBits(STOP_2);*/
    sp->setBaudRate(BAUD115200);
    sp->setDataBits(DATA_8);
    sp->setFlowControl(FLOW_OFF);
    sp->setParity(PAR_NONE);
    sp->setStopBits(STOP_1);
    sp->open(QIODevice::ReadWrite);
    connect(sp,SIGNAL(readyRead()),this,SLOT(ReadData()));

}

void SerialPort::ReadData()
{
    QByteArray ba;
    ba.resize(512);
    ba=sp->readAll();
    emit DataRecieve(ba);
}

this code run on Ubuntu at first and show all the bytes which receive from device, but when I tested it in linux embedded device this code read data from serial device in 2 part. () there is no \n in my bytes.
How can I solve this problem?

karti gesar

how much size of data u are reading

MhM93

some times 48 bit:

"aa552401040000000000000000000000"
"0000000000002801"

some time512 bit

karti gesar

void SerialPort::ReadData()
{
if (serial->bytesAvailable()>0||serial->waitForReadyRead(10000))
{
QByteArray ba;
ba=serial->readAll();
}
}
try this

MhM93

No. there is no diffrent :

4
"aa5524010400000000000000"
12
"000000000000000000002801"

for this code:

void SerialPort::ReadData()
{
    QByteArray ba;
    ba.resize(512);
    if(sp->bytesAvailable()>0 || sp->waitForReadyRead(20000))
    {
    qDebug()<<sp->bytesAvailable();
    ba=sp->readAll();
    qDebug()<<ba.toHex();
    emit DataRecieve(ba);
    }
}

mrjj

Hi
There is never a guarantee that bytes sent on a
serial line is received as one stream/read.

Therefore it is often needed to include data markers in the input to
know when all has been read or use fixed size blocks.

So when readyRead signal is sent. you read what there is with readAll() and append to a buffer.

if enough data is read OR data marker seen, then you emit DataRecieve().

MhM93

@mrjj thanks for help. I think maybe I have mistake in my code. so often the serial port can not read all of the data? . My serial device always send check sum at end of data, so I should check the data that receive and if the checksum is not true again listen run port.readall and attach the second data to the first and if it is true then emit the data.
Is it true?

mrjj

@MhM93

hi
Its normal that not all data can be read in one go. Often seen when moving from
PC to small(er) board.

The checksum sounds right way to know when all data been read or to catch transmission errors.
And yes, the logic if like that. On readyRead, read what there is. Append to the running buffer ( a member variable). When checksum is ok, emit signal. This logic will work fine as long there is
no chance that another data is sent while we wait for the rest of the first one.

MhM93

thanksss a lotttt :)