Strange QSerialport Problem

Artemus

Hi,

i want to write a small library to communicate with an external device using a virtual COM-Port.
Open the port an sending data works fine and the device also sends a correct response with about 6ms delay (i can see it on Oscilloscope).

However i can't read data using the asynchronous (non-blocking) approach.

The Idea was that I send a command to the device and the using QTimer::singleShot to wait some time and call a Slot that reads the response. The Problem is that i get "QIODevice::read: device not open" error when trying to read data in my receiving-Slot but if i try to read in my sending-function there is no error.

Here's the Code:

@typedef struct{
bool b_is_alive;
bool b_is_setup;
double f64_voltage;
double f64_current;
bool b_OutputIsOn;
bool b_CurrentLimitActive;
QString q_FailString;
}ST_LPS_OUT;

typedef struct{
QString q_ComPortName;
double f64_Voltage;
double f64_CurrentLimit;
bool b_EnableOutput;
}ST_LPS_SETUP;

class libZentroLPS358 : public QObject
{
Q_OBJECT
public:
explicit libZentroLPS358(QObject *parent = 0);
public slots:
void LPSsetup(ST_LPS_SETUP st_setup);
void AwaitingResponse(void);
signals:
void LPSnewData(ST_LPS_OUT st_out);

private:
bool ConnectLPS(QString q_portname);
QSerialPort* pq_comport;
ST_LPS_SETUP st_setupold;
ST_LPS_OUT st_out;
};@

@bool libZentroLPS358::ConnectLPS(QString q_portname)
{
bool b_ret;
bool b_continue;
float64 f64_wait_ms;
QString q_response;
uint8 au8_buffer[256];
uint8 u8_errorcounter;

//Create Comport instance
//pq_comport->QSerialPort::~QSerialPort();
pq_comport = new QSerialPort();
QSerialPort* pq_comport = new QSerialPort(q_portname);
b_ret = pq_comport->open( QIODevice::ReadWrite);
if(!b_ret)
{
    qDebug() << "failed to create com port instance";
    return true;
}

//Set up Comport
pq_comport->setBaudRate(38400);
pq_comport->setFlowControl(QSerialPort::HardwareControl);
pq_comport->setDataBits(QSerialPort::Data8);
pq_comport->setParity(QSerialPort::NoParity);
pq_comport->setStopBits(QSerialPort::OneStop);

//Ask Device to Identify itself
pq_comport->setRequestToSend(true);
pq_comport->write("*IDN?\r\n");
b_ret = pq_comport->waitForBytesWritten(f64_wait_ms);

QTimer::singleShot(50, this, SLOT(AwaitingResponse()));

}

void libZentroLPS358::AwaitingResponse(void)
{
pq_comport->waitForReadyRead(500);
char buff[256];
int i = pq_comport->read(buff,255);
}@

McLion

Are you sure your QSerialPort object is alive and can be accessed when you try to access it from AwaitingResponse?

Artemus

It should, i dont know why it should get closed within some ms. I moved the relevant code to as small new Project and get the same Error. Maybe you can compile and try it on your machine?

Download:
http://s000.tinyupload.com/?file_id=61057583527003946336

Output on my PC looks like this:
@-> MainWindow constructor
-> ConnectLPS Slot
INFO: setting up com port done
INFO: Comport is still open
INFO: sending *IDN? command
INFO: Comport is still open
INFO: transfer complete
INFO: Comport is still open
INFO: starting Timer
-> AwaitingResponse Slot
ERROR: Comport is not open!!!@

@#include "mainwindow.h"
#include "ui_mainwindow.h"

MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
ui->textBrowser->append("-> MainWindow constructor");
emit(ConnectLPS());
}

MainWindow::~MainWindow()
{
delete ui;
}

void MainWindow::ConnectLPS(void)
{
ui->textBrowser->append("-> ConnectLPS Slot");
bool b_ret;
float64 f64_wait_ms;

pq_comport = new QSerialPort();
QSerialPort* pq_comport = new QSerialPort("COM1");
b_ret = pq_comport->open( QIODevice::ReadWrite);
if(!b_ret)
{
    ui->textBrowser->append("ERROR: failed to create com port instance");
    return;
}

//Set up Comport
pq_comport->setBaudRate(38400);
pq_comport->setFlowControl(QSerialPort::HardwareControl);
pq_comport->setDataBits(QSerialPort::Data8);
pq_comport->setParity(QSerialPort::NoParity);
pq_comport->setStopBits(QSerialPort::OneStop);
ui->textBrowser->append("INFO: setting up com port done");
if(pq_comport->isOpen()) ui->textBrowser->append("INFO: Comport is still open");
else ui->textBrowser->append("ERROR: Comport is not open!!!");

//Ask Device to Identify itself
pq_comport->setRequestToSend(true);
pq_comport->write("*IDN?\r\n");
ui->textBrowser->append("INFO: sending *IDN? command");
if(pq_comport->isOpen()) ui->textBrowser->append("INFO: Comport is still open");
else ui->textBrowser->append("ERROR: Comport is not open!!!");

b_ret = pq_comport->waitForBytesWritten(f64_wait_ms);
ui->textBrowser->append("INFO: transfer complete");
if(pq_comport->isOpen()) ui->textBrowser->append("INFO: Comport is still open");
else ui->textBrowser->append("ERROR: Comport is not open!!!");

ui->textBrowser->append("INFO: starting Timer");
QTimer::singleShot(200, this, SLOT(AwaitingResponse()));

}

void MainWindow::AwaitingResponse(void)
{
ui->textBrowser->append("-> AwaitingResponse Slot");
if(pq_comport->isOpen()) ui->textBrowser->append("INFO: Comport is still open");
else ui->textBrowser->append("ERROR: Comport is not open!!!");

pq_comport->waitForReadyRead(500);
char buff[256];
int i = pq_comport->read(buff,255);

}
@

McLion

I'd try to move
@ pq_comport = new QSerialPort();@

to the constructor.

Artemus

Ah, that the Mistake:
@pq_comport = new QSerialPort();
QSerialPort* pq_comport = new QSerialPort(q_portname);@
i overwrite my global pq_comport with a local Object of the same name. I obviously forget to comment out or delete the "QSerialPort* pq_comport = new QSerialPort(q_portname);"

Thank you