com0com works fine, real device does not

[Gili Tzabari]

Hi,

I am running the same application against com0com and a real hardware device. Sending bytes to com0com's port works fine, but blocks against the real hardware. That is, the write operation never completes.

If I use Putty against the device it works just fine so I am assuming something is wrong with my application. The odd thing is that (as far as I can tell) my application is using an *identical* configuration as Putty: 9600 8-N-1 with no flow control.

I tried invoking ClearCommError() but it indicates there are no errors, so I'm stumped. Any ideas on why the outbound write would hang?

Thanks,
Gili

[Gili Tzabari]

I just found the com0com trace file, which is very useful, thanks! What win32 functions correspond to the following lines?

2009/06/05 10:22:11.215 COM6/FP c0cIoControl GET_BAUD_RATE
2009/06/05 10:22:11.216 COM6/FP FdoPortIoCtl GET_BAUD_RATE BaudRate=9600, status=SUCCESS
2009/06/05 10:22:11.216 COM6/FP c0cIoControl GET_LINE_CONTROL
2009/06/05 10:22:11.217 COM6/FP FdoPortIoCtl GET_LINE_CONTROL StopBits=0 Parity=0 WordLength=8, status=SUCCESS
2009/06/05 10:22:11.218 COM6/FP c0cIoControl GET_CHARS
2009/06/05 10:22:11.218 COM6/FP FdoPortIoCtl GET_CHARS EofChar=0x0 ErrorChar=0x0 BreakChar=0x0 EventChar=0x0 XonChar=0x11 XoffChar=0x13, status=SUCCESS
2009/06/05 10:22:11.219 COM6/FP c0cIoControl GET_HANDFLOW
2009/06/05 10:22:11.219 COM6/FP FdoPortIoCtl GET_HANDFLOW Hand[DTR_CONTROL] Flow[RTS_CONTROL] XonLim=2048 XoffLim=512, status=SUCCESS
2009/06/05 10:22:11.220 COM6/FP c0cIoControl GET_BAUD_RATE
2009/06/05 10:22:11.220 COM6/FP FdoPortIoCtl GET_BAUD_RATE BaudRate=9600, status=SUCCESS
2009/06/05 10:22:11.221 COM6/FP c0cIoControl GET_LINE_CONTROL
2009/06/05 10:22:11.222 COM6/FP FdoPortIoCtl GET_LINE_CONTROL StopBits=0 Parity=0 WordLength=8, status=SUCCESS
2009/06/05 10:22:11.222 COM6/FP c0cIoControl GET_CHARS
2009/06/05 10:22:11.223 COM6/FP FdoPortIoCtl GET_CHARS EofChar=0x0 ErrorChar=0x0 BreakChar=0x0 EventChar=0x0 XonChar=0x11 XoffChar=0x13, status=SUCCESS
2009/06/05 10:22:11.223 COM6/FP c0cIoControl GET_HANDFLOW
2009/06/05 10:22:11.224 COM6/FP FdoPortIoCtl GET_HANDFLOW Hand[DTR_CONTROL] Flow[RTS_CONTROL] XonLim=2048 XoffLim=512, status=SUCCESS
2009/06/05 10:22:11.224 COM6/FP c0cIoControl SET_BAUD_RATE BaudRate=300
2009/06/05 10:22:11.225 COM6/FP c0cIoControl SET_RTS
2009/06/05 10:22:11.225 COM6/FP c0cIoControl SET_DTR
2009/06/05 10:22:11.226 COM6/FP c0cIoControl SET_LINE_CONTROL StopBits=0 Parity=0 WordLength=8
2009/06/05 10:22:11.226 COM6/FP c0cIoControl SET_CHARS EofChar=0x0 ErrorChar=0x0 BreakChar=0x0 EventChar=0x0 XonChar=0x11 XoffChar=0x13
2009/06/05 10:22:11.227 COM6/FP c0cIoControl SET_HANDFLOW Hand[DTR_CONTROL] Flow[RTS_CONTROL] XonLim=2048 XoffLim=512
2009/06/05 10:22:11.227 COM6/FP c0cIoControl SET_TIMEOUTS Read[Interval=1 Multiplier=0 Constant=0] Write[Multiplier=0 Constant=0]

I've got a trace log for Putty and another one for my application. I would like to reverse engineer what functions Putty is invoking and doing the same myself.

Thanks,
Gili

[Gili Tzabari]

I figured it out!

When flow control was disabled I was setting:

dcb.fDtrControl = DTR_CONTROL_DISABLE;
dcb.fRtsControl = RTS_CONTROL_DISABLE;

but the code should be:

dcb.fDtrControl = DTR_CONTROL_ENABLE;
dcb.fRtsControl = RTS_CONTROL_ENABLE;

Thanks again for com0com. It's truly a great piece of software!

Gili