QSerialPort::availablePorts reports portName available after unplugging

[mrjj]

@Jeff-Barnes
Hi
Have you checked that ubuntu does in fact remove
the dev name when you unplug the sub->serial device ?

[Jeff Barnes]

Before unplugging serial cable:

ls /dev/ttyUSB0
/dev/ttyUSB0

After:
ls /dev/ttyUSB0
ls: cannot access '/dev/ttyUSB0': No such file or directory

[Jeff Barnes]

@Jeff-Barnes IMO, this is a bug in QSerialPort/QSerialPortInfo implementation, because the serial port is de-registered with the computer when the serial cable is unplugged, yet QSerialPortInfo::availablePorts() still lists it.

However, in my particular use case, I worked around it by leaving the QSerialPort open, the serial cable plugged in and power cycling the board. The USB is providing power to the serial port, so it is still active.

[aha_1980]

Hi @Jeff-Barnes, it could be a bug indeed.

Which type of USB adapter is this? Can you post the dmesg lines after plugging the adapter in and out? @kuzulis, any more information for investigation needed?

[Jeff Barnes]

jbarnes@jbarnes-All-Series:~/rail/desktop-tools$ sudo dmesg -C
jbarnes@jbarnes-All-Series:~/rail/desktop-tools$ dmesg
[1370519.563632] usb 3-4: USB disconnect, device number 78
[1370519.563719] ftdi_sio ttyUSB0: FTDI USB Serial Device converter now disconnected from ttyUSB0
[1370519.563731] ftdi_sio 3-4:1.0: device disconnected
[1370527.159840] usb 3-4: new full-speed USB device number 81 using xhci_hcd
[1370527.293315] usb 3-4: New USB device found, idVendor=0403, idProduct=6001
[1370527.293317] usb 3-4: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[1370527.293318] usb 3-4: Product: FT232R USB UART
[1370527.293319] usb 3-4: Manufacturer: FTDI
[1370527.293321] usb 3-4: SerialNumber: A50285BI
[1370527.295768] ftdi_sio 3-4:1.0: FTDI USB Serial Device converter detected
[1370527.295805] usb 3-4: Detected FT232RL
[1370527.295939] usb 3-4: FTDI USB Serial Device converter now attached to ttyUSB0

[kuzulis]

QSerialPortInfo takes info from the udev... Usually if you keep a serial port open, and then unplug an USB cable, then it can show that a device still is present in system.

From your code it is unclear what do you do. You should try to check it in two variants:

1. Try to keep QSerialPort as open.
2. Try do not touch the QSeralPort at all.

PS: It is not a QSPI issue, most likelly, you should address it to systemd bug-tracker or the kernel dev-list.

[Jeff Barnes]

You are probably right.

If I put a sleep(1) after availablePorts(), I get accurate info and can even reconnect.

[Jeff Barnes]

This post is deleted!

[Jeff Barnes]

This post is deleted!

[Jeff Barnes]

@Jeff-Barnes

#include "jtagclient.h"

#include <unistd.h>
#include <QSerialPortInfo>
#include <QTimer>

QString JtagClient::m_usbDevice = "ttyUSB0";

JtagClient::JtagClient(QObject *parent)
   :   QObject(parent)
{
   m_serialPort = new QSerialPort(m_usbDevice);
}

void JtagClient::run()
{
   if (!m_serialPort->open(QIODevice::ReadWrite))
   {
       emit usbDeviceStatus("Could not open serial port");
       return;
   }
   QTimer *tm = new QTimer;
   QTimer *retmr = new QTimer;
   tm->setInterval(500);
   tm->setSingleShot(false);
   retmr->setInterval(500);
   retmr->setSingleShot(false);
   QObject::connect(this, &JtagClient::stopDisconnectTimer, tm, &QTimer::stop);
   QObject::connect(this, &JtagClient::stopReconnectTimer, retmr, &QTimer::stop);
   QObject::connect(this, SIGNAL(startReconnectTimer()), retmr, SLOT(start()));
   QObject::connect(this, &JtagClient::finished, tm, &QTimer::deleteLater);
   QObject::connect(this, &JtagClient::finished, retmr, &QTimer::deleteLater);
   QObject::connect(tm, &QTimer::timeout, [&]() {
       bool found = false;
       foreach (QSerialPortInfo inf, QSerialPortInfo::availablePorts())
       {
           if (m_usbDevice == inf.portName())
           {
               emit usbDeviceStatus("Waiting for usb serial disconnect");
               found = true;
               break;
           }
       }
       if (!found)
       {
           m_serialPort->close();
           m_serialPort->deleteLater();
           emit usbDeviceStatus("Cable removed");
           emit stopDisconnectTimer();
           emit startReconnectTimer();
       }
   });
   QObject::connect(retmr, &QTimer::timeout, [&]() {
       bool found = false;
       foreach (QSerialPortInfo inf, QSerialPortInfo::availablePorts())
       {
           if (m_usbDevice == inf.portName())
           {
               found = true;
               //500000 causes a Permission denied error, presumably the kernel hasn't finished the inode
               //750000 causes a Permission denied error for ReadWrite, but works for ReadOnly
               //usleep(750000);
               sleep(1);
               m_serialPort = new QSerialPort(m_usbDevice);
               if (!m_serialPort->open(QIODevice::ReadWrite))
               {
                   emit usbDeviceStatus(QString("Could not re-open device: %1").arg(m_serialPort->errorString()));
               }
               else
               {
                   emit usbDeviceStatus("Connection re-established");
               }
               break;
           }
       }
       if (found)
       {
           emit stopReconnectTimer();
           emit finished();
       }
       else
           emit usbDeviceStatus("Waiting for re-connect");
   });
   tm->start();
}