QSerialPort write failure

JovanM

Hello.
I have some problem with writing data to serial COM port. Sometimes the queries do not complete and get "stuck", making port unusable. I'm adding a picture with the problem (captured using PortMon)
qSerialPort bad behavior

0	0.06566457	SomeGraphicalA	IRP_MJ_CREATE	VCP0	SUCCESS	Options: Open 	
1	0.00000279	SomeGraphicalA	IRP_MJ_CLEANUP	VCP0	SUCCESS		
2	5.09850628	SomeGraphicalA	IRP_MJ_CLOSE	VCP0	SUCCESS		
3	5.03382300	SomeGraphicalA	IRP_MJ_CREATE	VCP0	SUCCESS	Options: Open 	
4	0.00000349	SomeGraphicalA	IOCTL_SERIAL_GET_BAUD_RATE	VCP0	SUCCESS		
5	0.00000105	SomeGraphicalA	IOCTL_SERIAL_GET_LINE_CONTROL	VCP0	SUCCESS		
6	0.00000070	SomeGraphicalA	IOCTL_SERIAL_GET_CHARS	VCP0	SUCCESS		
7	0.00000070	SomeGraphicalA	IOCTL_SERIAL_GET_HANDFLOW	VCP0	SUCCESS		
8	0.00000070	SomeGraphicalA	IOCTL_SERIAL_GET_BAUD_RATE	VCP0	SUCCESS		
9	0.00000070	SomeGraphicalA	IOCTL_SERIAL_GET_LINE_CONTROL	VCP0	SUCCESS		
10	0.00000035	SomeGraphicalA	IOCTL_SERIAL_GET_CHARS	VCP0	SUCCESS		
11	0.00000070	SomeGraphicalA	IOCTL_SERIAL_GET_HANDFLOW	VCP0	SUCCESS		
12	0.00029044	SomeGraphicalA	IOCTL_SERIAL_SET_BAUD_RATE	VCP0	SUCCESS	Rate: 9600	
13	0.00036305	SomeGraphicalA	IOCTL_SERIAL_CLR_RTS	VCP0	SUCCESS		
14	0.00028800	SomeGraphicalA	IOCTL_SERIAL_SET_DTR	VCP0	SUCCESS		
15	0.00030441	SomeGraphicalA	IOCTL_SERIAL_SET_LINE_CONTROL	VCP0	SUCCESS	StopBits: 1 Parity: NONE WordLength: 8	
16	0.00000175	SomeGraphicalA	IOCTL_SERIAL_SET_CHAR	VCP0	SUCCESS	EOF:0 ERR:0 BRK:0 EVT:0 XON:11 XOFF:13	
17	0.00054353	SomeGraphicalA	IOCTL_SERIAL_SET_HANDFLOW	VCP0	SUCCESS	Shake:1 Replace:0 XonLimit:2048 XoffLimit:512	
18	0.00000175	SomeGraphicalA	IOCTL_SERIAL_GET_TIMEOUTS	VCP0	SUCCESS		
19	0.00000070	SomeGraphicalA	IOCTL_SERIAL_SET_TIMEOUTS	VCP0	SUCCESS	RI:-1 RM:0 RC:0 WM:0 WC:0	
20	0.00024087	SomeGraphicalA	IOCTL_SERIAL_SET_WAIT_MASK	VCP0	SUCCESS	Mask: RXCHAR 	
21	0.00000000	SomeGraphicalA	IOCTL_SERIAL_WAIT_ON_MASK	VCP0			
22	0.03217006	SomeGraphicalA	IRP_MJ_WRITE	VCP0	* 0xC0000001	Length 7: 10 03 00 01 00 01 D6

The last record means that write operation finished with error. I ask the user with parameters in graphical dialog and connect to port like this:

void MainWindow::connectDevice(DialogCOMPort::Settings inp_settings) {
    if (serialPort!=NULL) {
        //serial port was created before, just closing
        QSerialPortInfo *serialPortInfo = new QSerialPortInfo(*serialPort);
        if (serialPortInfo->isBusy()) {
            qDebug("On connecting Device... Something wrong has happened, serial port is broken");
        }
        if (serialPort->isOpen()) {
            serialPort->close();
        }
    } else {
        serialPort = new QSerialPort();
        this->writeUtil = new SerialPortWriter(serialPort);
        connect(serialPort, &QSerialPort::readyRead, this, &MainWindow::readReady);
    }
    serialPort->setBaudRate(inp_settings.baud);
    serialPort->setPortName(inp_settings.portAddr);
    serialPort->setDataBits(inp_settings.dataBits);
    serialPort->setStopBits(inp_settings.stopBits);
    serialPort->setParity(inp_settings.parity);
    serialPort->open(QSerialPort::ReadWrite);

}

and the Settings structure:

struct Settings {
        QString portAddr = "";
        QSerialPort::Parity parity = QSerialPort::EvenParity;
        QSerialPort::BaudRate baud = QSerialPort::Baud19200;
        QSerialPort::DataBits dataBits = QSerialPort::Data8;
        QSerialPort::StopBits stopBits = QSerialPort::OneStop;
        int responseTime = 1000;
        int numberOfRetries = 3;
    };

I write to comport like it is shown in example:

void SerialPortWriter::handleBytesWritten(qint64 bytes)
{
    m_bytesWritten += bytes;
    if (m_bytesWritten == m_writeData.size()) {
        m_bytesWritten = 0;
        QString msg=QObject::tr("Data successfully sent to port %1").arg(m_serialPort->portName());
        qDebug(msg.toStdString().c_str());
        //m_standardOutput << msg << endl;
        //QCoreApplication::quit();
    }
}

After I get such state in PortMon, all further writing operations are failing and when I try to close port, I get that IRP_MJ_Cleanup succeeds, but IRP_MJ_CLOSE hangs. So I cannot reopen port, only reboot makes port back online.
I'm using qt 5.8 on Win7, 32bit (bundled with mingw, installed just a week ago)

What should I do to make COM port connection working?

JovanM

@JovanM
I've checked, I'm using the same port options (baud, parity, start bits, stop bits...) as defined in port's options in device manager.

This problem appears from time to time, not often, a "ghast" one I'd say.
Nothing is connected to this port (at the time of testing), just sending bytes to it.

hskoglund

Hi, just guessing but perhaps you also need to turn off xon/xoff, try adding:

serialPort->setStopBits(inp_settings.stopBits);
....
serialPort->setFlowControl(QSerialPort::NoFlowControl);
...
serialPort->setParity(inp_settings.parity);
serialPort->open(QSerialPort::ReadWrite);

JovanM

@hskoglund
The docum. says:

The default value is NoFlowControl, i.e. no flow control.

So that construction seems more likely a wizardry, ~~but it gave a result~~ actually the problem is still here:

0	0.01104905	SomeGraphicalA	IRP_MJ_CREATE	VCP0	SUCCESS	Options: Open 	
1	0.00000244	SomeGraphicalA	IRP_MJ_CLEANUP	VCP0	SUCCESS		
2	0.11511006	SomeGraphicalA	IRP_MJ_CLOSE	VCP0	SUCCESS		
3	0.00302975	SomeGraphicalA	IRP_MJ_CREATE	VCP0	SUCCESS	Options: Open 	
4	0.00000140	SomeGraphicalA	IOCTL_SERIAL_GET_BAUD_RATE	VCP0	SUCCESS		
5	0.00000035	SomeGraphicalA	IOCTL_SERIAL_GET_LINE_CONTROL	VCP0	SUCCESS		
6	0.00000035	SomeGraphicalA	IOCTL_SERIAL_GET_CHARS	VCP0	SUCCESS		
7	0.00000035	SomeGraphicalA	IOCTL_SERIAL_GET_HANDFLOW	VCP0	SUCCESS		
8	0.00000035	SomeGraphicalA	IOCTL_SERIAL_GET_BAUD_RATE	VCP0	SUCCESS		
9	0.00000000	SomeGraphicalA	IOCTL_SERIAL_GET_LINE_CONTROL	VCP0	SUCCESS		
10	0.00000035	SomeGraphicalA	IOCTL_SERIAL_GET_CHARS	VCP0	SUCCESS		
11	0.00000035	SomeGraphicalA	IOCTL_SERIAL_GET_HANDFLOW	VCP0	SUCCESS		
12	0.00010298	SomeGraphicalA	IOCTL_SERIAL_SET_BAUD_RATE	VCP0	SUCCESS	Rate: 9600	
13	0.00009530	SomeGraphicalA	IOCTL_SERIAL_CLR_RTS	VCP0	SUCCESS		
14	0.00023948	SomeGraphicalA	IOCTL_SERIAL_SET_DTR	VCP0	SUCCESS		
15	0.00012393	SomeGraphicalA	IOCTL_SERIAL_SET_LINE_CONTROL	VCP0	SUCCESS	StopBits: 1 Parity: NONE WordLength: 8	
16	0.00000035	SomeGraphicalA	IOCTL_SERIAL_SET_CHAR	VCP0	SUCCESS	EOF:0 ERR:0 BRK:0 EVT:0 XON:11 XOFF:13	
17	0.00033233	SomeGraphicalA	IOCTL_SERIAL_SET_HANDFLOW	VCP0	SUCCESS	Shake:1 Replace:0 XonLimit:2048 XoffLimit:512	
18	0.00000035	SomeGraphicalA	IOCTL_SERIAL_GET_TIMEOUTS	VCP0	SUCCESS		
19	0.00000035	SomeGraphicalA	IOCTL_SERIAL_SET_TIMEOUTS	VCP0	SUCCESS	RI:-1 RM:0 RC:0 WM:0 WC:0	
20	0.00009775	SomeGraphicalA	IOCTL_SERIAL_SET_WAIT_MASK	VCP0	SUCCESS	Mask: RXCHAR 	
21	230.15856027	SomeGraphicalA	IOCTL_SERIAL_WAIT_ON_MASK	VCP0	CANCELLED		
22	0.00028381	SomeGraphicalA	IRP_MJ_WRITE	VCP0	SUCCESS	Length 7: 10 03 00 01 00 01 D6 	
23	0.00022796	SomeGraphicalA	IRP_MJ_WRITE	VCP0	SUCCESS	Length 7: 10 03 00 02 00 01 26 	
24	0.00001466	SomeGraphicalA	IRP_MJ_CLEANUP	VCP0	SUCCESS		
25	0.10910221	SomeGraphicalA	IRP_MJ_CLOSE	VCP0	SUCCESS		
26	0.06496813	SomeGraphicalA	IRP_MJ_CREATE	VCP0	SUCCESS	Options: Open 	
27	0.00000244	SomeGraphicalA	IRP_MJ_CLEANUP	VCP0	SUCCESS		
28	5.09932105	SomeGraphicalA	IRP_MJ_CLOSE	VCP0	SUCCESS		
29	5.03467199	SomeGraphicalA	IRP_MJ_CREATE	VCP0	SUCCESS	Options: Open 	
30	0.00000279	SomeGraphicalA	IOCTL_SERIAL_GET_BAUD_RATE	VCP0	SUCCESS		
31	0.00000105	SomeGraphicalA	IOCTL_SERIAL_GET_LINE_CONTROL	VCP0	SUCCESS		
32	0.00000105	SomeGraphicalA	IOCTL_SERIAL_GET_CHARS	VCP0	SUCCESS		
33	0.00000070	SomeGraphicalA	IOCTL_SERIAL_GET_HANDFLOW	VCP0	SUCCESS		
34	0.00000105	SomeGraphicalA	IOCTL_SERIAL_GET_BAUD_RATE	VCP0	SUCCESS		
35	0.00000070	SomeGraphicalA	IOCTL_SERIAL_GET_LINE_CONTROL	VCP0	SUCCESS		
36	0.00000070	SomeGraphicalA	IOCTL_SERIAL_GET_CHARS	VCP0	SUCCESS		
37	0.00000035	SomeGraphicalA	IOCTL_SERIAL_GET_HANDFLOW	VCP0	SUCCESS		
38	0.00027194	SomeGraphicalA	IOCTL_SERIAL_SET_BAUD_RATE	VCP0	SUCCESS	Rate: 9600	
39	0.00051770	SomeGraphicalA	IOCTL_SERIAL_CLR_RTS	VCP0	SUCCESS		
40	0.00028835	SomeGraphicalA	IOCTL_SERIAL_SET_DTR	VCP0	SUCCESS		
41	0.00030022	SomeGraphicalA	IOCTL_SERIAL_SET_LINE_CONTROL	VCP0	SUCCESS	StopBits: 1 Parity: NONE WordLength: 8	
42	0.00000140	SomeGraphicalA	IOCTL_SERIAL_SET_CHAR	VCP0	SUCCESS	EOF:0 ERR:0 BRK:0 EVT:0 XON:11 XOFF:13	
43	0.00018118	SomeGraphicalA	IOCTL_SERIAL_SET_HANDFLOW	VCP0	SUCCESS	Shake:1 Replace:0 XonLimit:2048 XoffLimit:512	
44	0.00000105	SomeGraphicalA	IOCTL_SERIAL_GET_TIMEOUTS	VCP0	SUCCESS		
45	0.00000105	SomeGraphicalA	IOCTL_SERIAL_SET_TIMEOUTS	VCP0	SUCCESS	RI:-1 RM:0 RC:0 WM:0 WC:0	
46	0.00019828	SomeGraphicalA	IOCTL_SERIAL_SET_WAIT_MASK	VCP0	SUCCESS	Mask: RXCHAR 	
47	116.59613788	SomeGraphicalA	IOCTL_SERIAL_WAIT_ON_MASK	VCP0	CANCELLED		
48	0.03208767	SomeGraphicalA	IRP_MJ_WRITE	VCP0	* 0xC0000001	Length 7: 10 03 00 03 00 01 77 	
49	0.00000209	SomeGraphicalA	IRP_MJ_CLEANUP	VCP0	SUCCESS		
50	0.00000000	SomeGraphicalA	IRP_MJ_CLOSE	VCP0

The first time it was working like a charm, I've sent two requests on COM port (lines 22-23). I closed the program, took some break, restarted it and the problem is back (line 48. On line 50 we see that COM port hangs on closing).
That's a PortMon's log.

JovanM

@JovanM
After that PortMon dispatches nothing at all. After quiting from program, turning it back I cannot send anything to port, due to 'Access denied' error. (obviously)

SGaist

Hi,

What kind of serial port is the device you use ?

JovanM

@SGaist
This is USB Serial Port, produced by FTDI, with the latest drivers I've managed to find on official website.
It is actually a USB to RS-485 converter, but it maps as COM port in OS (truestory, it is being correctly shown as COM9 under the section 'COM and LPT ports' in device manager).

hskoglund

Perhaps try another program to see if your COM port hangs the same way, Windows XP had a free program called HyperTerminal, you can download a free 30-day trial for you Windows 7 here

JovanM

@hskoglund
Thank you for your answer. I've found that PuTTY.exe (another connection soft) also has capability to send bytes to COM port. And everything worked like a charm (in putty, sure). Here's a fragment of my testing:

5	0.01122259	putty.exe	IRP_MJ_CREATE	VCP0	SUCCESS	Options: Open 	
46	0.00000279	putty.exe	IOCTL_SERIAL_GET_BAUD_RATE	VCP0	SUCCESS		
47	0.00000105	putty.exe	IOCTL_SERIAL_GET_LINE_CONTROL	VCP0	SUCCESS		
48	0.00000105	putty.exe	IOCTL_SERIAL_GET_CHARS	VCP0	SUCCESS		
49	0.00000070	putty.exe	IOCTL_SERIAL_GET_HANDFLOW	VCP0	SUCCESS		
50	0.00000105	putty.exe	IOCTL_SERIAL_GET_BAUD_RATE	VCP0	SUCCESS		
51	0.00000035	putty.exe	IOCTL_SERIAL_GET_LINE_CONTROL	VCP0	SUCCESS		
52	0.00000035	putty.exe	IOCTL_SERIAL_GET_CHARS	VCP0	SUCCESS		
53	0.00000035	putty.exe	IOCTL_SERIAL_GET_HANDFLOW	VCP0	SUCCESS		
54	0.00026182	putty.exe	IOCTL_SERIAL_SET_BAUD_RATE	VCP0	SUCCESS	Rate: 9600	
55	0.00015604	putty.exe	IOCTL_SERIAL_SET_RTS	VCP0	SUCCESS		
56	0.00013091	putty.exe	IOCTL_SERIAL_SET_DTR	VCP0	SUCCESS		
57	0.00021015	putty.exe	IOCTL_SERIAL_SET_LINE_CONTROL	VCP0	SUCCESS	StopBits: 1 Parity: NONE WordLength: 8	
58	0.00000105	putty.exe	IOCTL_SERIAL_SET_CHAR	VCP0	SUCCESS	EOF:0 ERR:0 BRK:0 EVT:0 XON:11 XOFF:13	
59	0.00019165	putty.exe	IOCTL_SERIAL_SET_HANDFLOW	VCP0	SUCCESS	Shake:1 Replace:40 XonLimit:2048 XoffLimit:512	
60	0.00000105	putty.exe	IOCTL_SERIAL_SET_TIMEOUTS	VCP0	SUCCESS	RI:1 RM:0 RC:0 WM:0 WC:0	
61	52.21592939	putty.exe	IRP_MJ_READ	VCP0	CANCELLED	Length 1	
62	0.00016268	putty.exe	IRP_MJ_WRITE	VCP0	SUCCESS	Length 1: H	
63	0.00022097	putty.exe	IRP_MJ_WRITE	VCP0	SUCCESS	Length 1: e	
64	0.00021225	putty.exe	IRP_MJ_WRITE	VCP0	SUCCESS	Length 1: l	
65	0.00033792	putty.exe	IRP_MJ_WRITE	VCP0	SUCCESS	Length 1: l	
66	0.00029114	putty.exe	IRP_MJ_WRITE	VCP0	SUCCESS	Length 1: o	
67	0.00021120	putty.exe	IRP_MJ_WRITE	VCP0	SUCCESS	Length 1:  	
68	0.00026950	putty.exe	IRP_MJ_WRITE	VCP0	SUCCESS	Length 1: W	
69	0.00033024	putty.exe	IRP_MJ_WRITE	VCP0	SUCCESS	Length 1: o	
70	0.00019409	putty.exe	IRP_MJ_WRITE	VCP0	SUCCESS	Length 1: r	
71	0.00031488	putty.exe	IRP_MJ_WRITE	VCP0	SUCCESS	Length 1: l	
72	0.00020422	putty.exe	IRP_MJ_WRITE	VCP0	SUCCESS	Length 1: d	
73	0.00014732	putty.exe	IRP_MJ_WRITE	VCP0	SUCCESS	Length 1: l	
74	0.00020177	putty.exe	IRP_MJ_WRITE	VCP0	SUCCESS	Length 1: l	
75	0.00025239	putty.exe	IRP_MJ_WRITE	VCP0	SUCCESS	Length 1: l	
76	0.00033513	putty.exe	IRP_MJ_WRITE	VCP0	SUCCESS	Length 1: .	
77	0.00000349	putty.exe	IRP_MJ_CLEANUP	VCP0	SUCCESS		
78	0.11307382	putty.exe	IRP_MJ_CLOSE	VCP0	SUCCESS

Everything seems to be the same, but putty does not send IOCTL_SERIAL_SET_WAIT_MASK and IOCTL_SERIAL_WAIT_ON_MASK commands, which QT does

Maybe because of this signal my port hangs. Is there any way to control such behavior?

JovanM

And here is the log fragment for HyperTerm.

79	0.01420278	hypertrm.exe	IRP_MJ_CREATE	VCP0	SUCCESS	Options: Open 	
80	0.00000663	hypertrm.exe	IOCTL_SERIAL_SET_QUEUE_SIZE	VCP0	SUCCESS	InSize: 8192 OutSize: 8192	
81	0.00000105	hypertrm.exe	IOCTL_SERIAL_CONFIG_SIZE	VCP0	SUCCESS	Size: 0	
82	0.00000105	hypertrm.exe	IOCTL_SERIAL_GET_BAUD_RATE	VCP0	SUCCESS		
83	0.00000105	hypertrm.exe	IOCTL_SERIAL_GET_LINE_CONTROL	VCP0	SUCCESS		
84	0.00000244	hypertrm.exe	IOCTL_SERIAL_GET_CHARS	VCP0	SUCCESS		
85	0.00000105	hypertrm.exe	IOCTL_SERIAL_GET_HANDFLOW	VCP0	SUCCESS		
86	0.00000070	hypertrm.exe	IOCTL_SERIAL_GET_BAUD_RATE	VCP0	SUCCESS		
87	0.00000070	hypertrm.exe	IOCTL_SERIAL_GET_LINE_CONTROL	VCP0	SUCCESS		
88	0.00000070	hypertrm.exe	IOCTL_SERIAL_GET_CHARS	VCP0	SUCCESS		
89	0.00000070	hypertrm.exe	IOCTL_SERIAL_GET_HANDFLOW	VCP0	SUCCESS		
90	0.00024576	hypertrm.exe	IOCTL_SERIAL_SET_BAUD_RATE	VCP0	SUCCESS	Rate: 9600	
91	0.00027927	hypertrm.exe	IOCTL_SERIAL_SET_RTS	VCP0	SUCCESS		
92	0.00015220	hypertrm.exe	IOCTL_SERIAL_SET_DTR	VCP0	SUCCESS		
93	0.00018781	hypertrm.exe	IOCTL_SERIAL_SET_LINE_CONTROL	VCP0	SUCCESS	StopBits: 1 Parity: NONE WordLength: 8	
94	0.00000105	hypertrm.exe	IOCTL_SERIAL_SET_CHAR	VCP0	SUCCESS	EOF:0 ERR:0 BRK:0 EVT:0 XON:11 XOFF:13	
95	0.00021469	hypertrm.exe	IOCTL_SERIAL_SET_HANDFLOW	VCP0	SUCCESS	Shake:80000001 Replace:80000040 XonLimit:80 XoffLimit:200	
96	0.00000105	hypertrm.exe	IOCTL_SERIAL_SET_TIMEOUTS	VCP0	SUCCESS	RI:10 RM:0 RC:0 WM:0 WC:5000	
97	0.00020911	hypertrm.exe	IOCTL_SERIAL_SET_WAIT_MASK	VCP0	SUCCESS	Mask: RLSD ERR 	
98	149.25617403	hypertrm.exe	IOCTL_SERIAL_WAIT_ON_MASK	VCP0	SUCCESS		
99	149.25617263	hypertrm.exe	IRP_MJ_READ	VCP0	CANCELLED	Length 80	
100	0.00033059	hypertrm.exe	IRP_MJ_WRITE	VCP0	SUCCESS	Length 1: H	
101	0.00029254	hypertrm.exe	IRP_MJ_WRITE	VCP0	SUCCESS	Length 1: e	
102	0.00028695	hypertrm.exe	IRP_MJ_WRITE	VCP0	SUCCESS	Length 1: l	
103	0.00032465	hypertrm.exe	IRP_MJ_WRITE	VCP0	SUCCESS	Length 1: l	
104	0.00018048	hypertrm.exe	IRP_MJ_WRITE	VCP0	SUCCESS	Length 1: o	
105	0.00016966	hypertrm.exe	IRP_MJ_WRITE	VCP0	SUCCESS	Length 1:  	
106	0.00026391	hypertrm.exe	IRP_MJ_WRITE	VCP0	SUCCESS	Length 1: T	
107	0.00020073	hypertrm.exe	IRP_MJ_WRITE	VCP0	SUCCESS	Length 1: h	
108	0.00036096	hypertrm.exe	IRP_MJ_WRITE	VCP0	SUCCESS	Length 1: e	
109	0.00016407	hypertrm.exe	IRP_MJ_WRITE	VCP0	SUCCESS	Length 1: r	
110	0.00016791	hypertrm.exe	IRP_MJ_WRITE	VCP0	SUCCESS	Length 1: e	
111	0.00023215	hypertrm.exe	IRP_MJ_WRITE	VCP0	SUCCESS	Length 1: N	
112	0.00025868	hypertrm.exe	IRP_MJ_WRITE	VCP0	SUCCESS	Length 1: o	
113	0.00017315	hypertrm.exe	IRP_MJ_WRITE	VCP0	SUCCESS	Length 1: t	
114	0.00022726	hypertrm.exe	IRP_MJ_WRITE	VCP0	SUCCESS	Length 1:  	
115	0.00030860	hypertrm.exe	IRP_MJ_WRITE	VCP0	SUCCESS	Length 1: H	
116	0.00021399	hypertrm.exe	IRP_MJ_WRITE	VCP0	SUCCESS	Length 1: a	
117	0.00016756	hypertrm.exe	IRP_MJ_WRITE	VCP0	SUCCESS	Length 1: n	
118	0.00019968	hypertrm.exe	IRP_MJ_WRITE	VCP0	SUCCESS	Length 1: g	
119	0.00018223	hypertrm.exe	IRP_MJ_WRITE	VCP0	SUCCESS	Length 1: i	
120	0.00031069	hypertrm.exe	IRP_MJ_WRITE	VCP0	SUCCESS	Length 1: n	
121	0.00019444	hypertrm.exe	IRP_MJ_WRITE	VCP0	SUCCESS	Length 1: g	
122	0.00021748	hypertrm.exe	IRP_MJ_WRITE	VCP0	SUCCESS	Length 1: ?	
123	0.00026147	hypertrm.exe	IRP_MJ_WRITE	VCP0	SUCCESS	Length 1: W	
124	0.00034351	hypertrm.exe	IRP_MJ_WRITE	VCP0	SUCCESS	Length 1: e	
125	0.00029149	hypertrm.exe	IRP_MJ_WRITE	VCP0	SUCCESS	Length 1: l	
126	0.00016407	hypertrm.exe	IRP_MJ_WRITE	VCP0	SUCCESS	Length 1: l	
127	0.00011171	hypertrm.exe	IRP_MJ_WRITE	VCP0	SUCCESS	Length 1: H	
128	0.00000349	hypertrm.exe	IOCTL_SERIAL_GET_COMMSTATUS	VCP0	SUCCESS		
129	0.00024227	hypertrm.exe	IRP_MJ_WRITE	VCP0	SUCCESS	Length 1: e	
130	0.00000140	hypertrm.exe	IOCTL_SERIAL_GET_COMMSTATUS	VCP0	SUCCESS		
131	0.00020457	hypertrm.exe	IRP_MJ_WRITE	VCP0	SUCCESS	Length 1: r	
132	0.00000175	hypertrm.exe	IOCTL_SERIAL_GET_COMMSTATUS	VCP0	SUCCESS		
133	0.00027718	hypertrm.exe	IRP_MJ_WRITE	VCP0	SUCCESS	Length 1: e	
134	0.00000175	hypertrm.exe	IOCTL_SERIAL_GET_COMMSTATUS	VCP0	SUCCESS		
135	0.00024052	hypertrm.exe	IRP_MJ_WRITE	VCP0	SUCCESS	Length 1:  	
136	0.00000175	hypertrm.exe	IOCTL_SERIAL_GET_COMMSTATUS	VCP0	SUCCESS		
137	0.00031279	hypertrm.exe	IRP_MJ_WRITE	VCP0	SUCCESS	Length 1: c	
138	0.00000209	hypertrm.exe	IOCTL_SERIAL_GET_COMMSTATUS	VCP0	SUCCESS		
139	0.00021469	hypertrm.exe	IRP_MJ_WRITE	VCP0	SUCCESS	Length 1: o	
140	0.00000175	hypertrm.exe	IOCTL_SERIAL_GET_COMMSTATUS	VCP0	SUCCESS		
141	0.00020771	hypertrm.exe	IRP_MJ_WRITE	VCP0	SUCCESS	Length 1: m	
142	0.00000140	hypertrm.exe	IOCTL_SERIAL_GET_COMMSTATUS	VCP0	SUCCESS		
143	0.00019968	hypertrm.exe	IRP_MJ_WRITE	VCP0	SUCCESS	Length 1: e	
144	0.00000175	hypertrm.exe	IOCTL_SERIAL_GET_COMMSTATUS	VCP0	SUCCESS		
145	0.00021644	hypertrm.exe	IRP_MJ_WRITE	VCP0	SUCCESS	Length 1: s	
146	0.00000140	hypertrm.exe	IOCTL_SERIAL_GET_COMMSTATUS	VCP0	SUCCESS		
147	0.00020980	hypertrm.exe	IRP_MJ_WRITE	VCP0	SUCCESS	Length 1:  	
148	0.00000175	hypertrm.exe	IOCTL_SERIAL_GET_COMMSTATUS	VCP0	SUCCESS		
149	0.00020806	hypertrm.exe	IRP_MJ_WRITE	VCP0	SUCCESS	Length 1: t	
150	0.00000140	hypertrm.exe	IOCTL_SERIAL_GET_COMMSTATUS	VCP0	SUCCESS		
151	0.00020806	hypertrm.exe	IRP_MJ_WRITE	VCP0	SUCCESS	Length 1: h	
152	0.00000175	hypertrm.exe	IOCTL_SERIAL_GET_COMMSTATUS	VCP0	SUCCESS		
153	0.00022481	hypertrm.exe	IRP_MJ_WRITE	VCP0	SUCCESS	Length 1: e	
154	0.00000140	hypertrm.exe	IOCTL_SERIAL_GET_COMMSTATUS	VCP0	SUCCESS		
155	0.00020911	hypertrm.exe	IRP_MJ_WRITE	VCP0	SUCCESS	Length 1:  	
156	0.00000140	hypertrm.exe	IOCTL_SERIAL_GET_COMMSTATUS	VCP0	SUCCESS		
157	0.00020596	hypertrm.exe	IRP_MJ_WRITE	VCP0	SUCCESS	Length 1: l	
158	0.00000209	hypertrm.exe	IOCTL_SERIAL_GET_COMMSTATUS	VCP0	SUCCESS		
159	0.00020247	hypertrm.exe	IRP_MJ_WRITE	VCP0	SUCCESS	Length 1: i	
160	0.00000175	hypertrm.exe	IOCTL_SERIAL_GET_COMMSTATUS	VCP0	SUCCESS		
161	0.00021364	hypertrm.exe	IRP_MJ_WRITE	VCP0	SUCCESS	Length 1: n	
162	0.00000175	hypertrm.exe	IOCTL_SERIAL_GET_COMMSTATUS	VCP0	SUCCESS		
163	0.00021295	hypertrm.exe	IRP_MJ_WRITE	VCP0	SUCCESS	Length 1: e	
164	0.00021609	hypertrm.exe	IOCTL_SERIAL_SET_WAIT_MASK	VCP0	SUCCESS	Mask: RLSD ERR 	
165	0.00000733	hypertrm.exe	IOCTL_SERIAL_PURGE	VCP0	SUCCESS	Purge: TXABORT RXABORT 	
166	0.00000279	hypertrm.exe	IRP_MJ_CLEANUP	VCP0	SUCCESS		
167	0.11072793	hypertrm.exe	IRP_MJ_CLOSE	VCP0	SUCCESS		
168	0.00965866	hypertrm.exe	IRP_MJ_CREATE	VCP0	SUCCESS	Options: Open 	
169	0.00000175	hypertrm.exe	IRP_MJ_QUERY_INFORMATION	VCP0	SUCCESS	-1567238140	
170	0.00000209	hypertrm.exe	IRP_MJ_CLEANUP	VCP0	SUCCESS		
171	0.11427330	hypertrm.exe	IRP_MJ_CLOSE	VCP0	SUCCESS

Probably those IOCTLs are not the reason, because hyperterm sends them too.
Should I send the data in a single symbol at a time, instead of sending data packages? I'm going to connect to device using a binary protocol and my message contains non-ascii chars (0x00 are pretty common in my messages).

kuzulis

You can try to open serial port in WriteOnly mode, in this case the RXCHA flag will not be set (if it confuses you).
You can try to use the Terminal example from QSP examples.

Also, please provide an error code and error text if it happens!

As I remember, the Putty does not work with serial port in overlapped mode. Also I'm not sure that the HyperTerm also works in overlapped mode (as I can see from your log).

PS: History shows, that the FTDI adapter never had problems on Windows. Maybe your PortMon get stuck, maybe latest FTDI drivers get stuck.. Maybe you need to change your HW to another FTDI adapter (as current may broken).

JovanM

I need not only write bytes but I need to be able to read them from port as defined in the task. Hardware does not belong to me, so I have to work with the provided devices.
The code works unreliably, sometimes it works, sometimes it does not.
That's weird.