Need explanation QSerialPort vs Pyserial

moscowbob

I'm trying to reset an Arduino Leonardo into boot loader mode by opening and closing the usb serial with a baudrate of 1200. This does not seem to work with Qt. When I tried this with PySerial, just opening and closing the port it works. I also tested with stty and that also works.

Does anybody have any ideas why QSerialPort does not work ?

void Programmer::resetAvr()
{
    m_port.setBaudRate(QSerialPort::Baud1200);
    m_port.setDataBits(QSerialPort::Data8);
    m_port.setParity(QSerialPort::NoParity);
    m_port.setStopBits(QSerialPort::OneStop);
    m_port.setFlowControl(QSerialPort::NoFlowControl);
    m_port.setPortName(m_portName);

    if(m_port.open(QIODevice::ReadWrite) == true)
    {
        m_port.close();
    }
}

#!/usr/bin/env python

import serial, sys

serialPort = sys.argv[1]
print serialPort

ser = serial.Serial(
    port=serialPort,
    baudrate=1200,
    parity=serial.PARITY_NONE,
    stopbits=serial.STOPBITS_ONE,
    bytesize=serial.EIGHTBITS
)
ser.isOpen()
ser.close()             # close port

stty -F /dev/ttyACM0 1200 cs8 -cstopb -parenb

moscowbob

Well after spending many hours digging through usb protocol documentation I have finally got to a point where I can say the problem is with QSerialPort. Since I cannot upload files I will try and explain.

PySerial and linux stty both exhibit the same behavior when viewed in wireshark usb capture:

Host send command 0x22 with value 0x03 to enable RTS and DTR
Host send comand 0x20 with 7 bytes data to configure BAUD, DATABITS, PARITY and STOPBITS
1200, 8, n, 1
Host send command 0x22 with value 0x00 to disable RTS/DTR

Now the device resets and goes into boot mode.

QSerialPort behaves as follows - Open/Close :

Host send command 0x22 with value 0x03 to enable RTS and DTR
Host send command 0x20 with 7 bytes data to configure BAUD, DATABITS, PARITY and STOPBITS
(all these configurations are sent)
400000, 8, n, 1
9600, 8, n, 1
1200, 8, n, 1
115200, 8, n, 1
Host send command 0x22 with value 0x00 to disable RTS and DTR

#include <QCoreApplication>
#include <QDebug>
#include <QSerialPort>

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);
    QSerialPort mPort;

    mPort.setBaudRate(QSerialPort::Baud1200);
    mPort.setDataBits(QSerialPort::Data8);
    mPort.setStopBits(QSerialPort::OneStop);
    mPort.setParity(QSerialPort::NoParity);
    mPort.setPortName("/dev/ttyACM0");

    qDebug() << "Open Port";
    mPort.open(QIODevice::ReadWrite);
    if(mPort.isOpen())
    {
        qDebug() << "Close Port";
        mPort.close();
    }

    exit(0);
//    return a.exec();
}

Anybody ??

aha_1980

Hi @moscowbob,

just opening and closing a serial port without sending data will not change anything for the other side (independent of the baud rate).

So there is most likely a control line (RTS, CTS, RTR) involved that actually does the reset? Do you have a description how the reset is supposed to work?

And if it is working like this, there can be indeed a difference between pyserial and QSerialPort.

moscowbob

@aha_1980 , thanks for response.
The connection is a USB CDC connection, the AT32U4 chip has an embedded usb that is configured as a virtual comport. So there are no control lines connected. As I understand, when the host opens the port, it will configure the device endpoint and it is there where the 1200 baud is used to reset the device into bootloader mode.

I have captured the usb conversation between the host pc and device for all 3 methods and the QSerialPort conversation looks completely different - unfortunately my knowledge is very limited when it comes to this, so if you want, I can post the three Wireshark capure files for viewing.

aha_1980

Hi @moscowbob,

yeah, you can post them, but I have to admit that my knowledge is also limited here :)

But maybe someone else can help you here...

moscowbob

What is the accepted method for the forum when posting files - I do not have privilege to upload here ?

Thanks

mrjj

@moscowbob
Hi
It only wants
alt text
What type are you trying ?

moscowbob

Thanks @mrjj ,
The capture files I have are wireshark .pcapng or a zip file containing all 3 captures.

mrjj

Not sure it will accept those.

moscowbob

No there is something else wrong, I just tried to upload a simple text file with .c extension and I just get the same message

" ERROR
You do not have enough privileges for this action."

moscowbob

Well after spending many hours digging through usb protocol documentation I have finally got to a point where I can say the problem is with QSerialPort. Since I cannot upload files I will try and explain.

PySerial and linux stty both exhibit the same behavior when viewed in wireshark usb capture:

Host send command 0x22 with value 0x03 to enable RTS and DTR
Host send comand 0x20 with 7 bytes data to configure BAUD, DATABITS, PARITY and STOPBITS
1200, 8, n, 1
Host send command 0x22 with value 0x00 to disable RTS/DTR

Now the device resets and goes into boot mode.

QSerialPort behaves as follows - Open/Close :

Host send command 0x22 with value 0x03 to enable RTS and DTR
Host send command 0x20 with 7 bytes data to configure BAUD, DATABITS, PARITY and STOPBITS
(all these configurations are sent)
400000, 8, n, 1
9600, 8, n, 1
1200, 8, n, 1
115200, 8, n, 1
Host send command 0x22 with value 0x00 to disable RTS and DTR

#include <QCoreApplication>
#include <QDebug>
#include <QSerialPort>

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);
    QSerialPort mPort;

    mPort.setBaudRate(QSerialPort::Baud1200);
    mPort.setDataBits(QSerialPort::Data8);
    mPort.setStopBits(QSerialPort::OneStop);
    mPort.setParity(QSerialPort::NoParity);
    mPort.setPortName("/dev/ttyACM0");

    qDebug() << "Open Port";
    mPort.open(QIODevice::ReadWrite);
    if(mPort.isOpen())
    {
        qDebug() << "Close Port";
        mPort.close();
    }

    exit(0);
//    return a.exec();
}

Anybody ??

moscowbob

Well, finally a breakthrough !

It turn out that the deprecated function

mPort.setSettingsRestoredOnClose(false);

Does the trick.

Although the Arduino now does reset, since QSerialPort does not send the restored values before closing the port, it still sends a garbage packet before setting the 1200 baud. I have not figured that one out yet, and I am now getting tired.

So I will mark this as solved but will raise another post to query the strange behavior when QSerialPort opens.

aha_1980

@moscowbob

Please report this at bugreports.qt.io (and provide a link to the bug here).

You will have better possibilities to discuss the behavior with the developers there and you should also be able to attach the Wireshark logs.

Thanks.