问题
I have some stupid code to access a Windows COM-port (just some pseudo-code of the most relevant functions):
// open device:
COMMTIMEOUTS timeouts;
DCB ComSettings;
memset(&ComSettings,0,sizeof(ComSettings));
ComSettings.DCBlength=sizeof(DCB);
*fd=CreateFile(serialParams>port,GENERIC_READ|GENERIC_WRITE,0,0,OPEN_EXISTING,0,0);
GetCommState(*fd,&ComSettings);
ComSettings.BaudRate=9600;
ComSettings.ByteSize=8;
ComSettings.Parity=NOPARITY;
ComSettings.fParity=0;
ComSettings.StopBits=ONESTOPBIT;
ComSettings.fOutX=FALSE;
ComSettings.fInX=FALSE;
ComSettings.fBinary=TRUE;
ComSettings.fDtrControl=DTR_CONTROL_DISABLE;
ComSettings.fRtsControl=RTS_CONTROL_DISABLE;
ComSettings.fAbortOnError=FALSE;
SetCommState(*fd,&ComSettings);
timeouts.ReadIntervalTimeout =MAXDWORD;
timeouts.ReadTotalTimeoutMultiplier =0;
timeouts.ReadTotalTimeoutConstant =0;
timeouts.WriteTotalTimeoutMultiplier=0;
timeouts.WriteTotalTimeoutConstant =250;
SetCommTimeouts(*fd, &timeouts);
Reading of data from serial port is done with
ReadFile()
and writing with
WriteFile()
In my particular case the device is a USB gadget which connects as serial interface and where speed-settings and other things do not really matter.
This code is working fine with all Windows variants including 8.1 but for Windows 10 some users report there is no communication possible with the device. Unfortunately I do not have the related Win10 version for testing.
So my question: are there some issues/important changes in Windows 10 which could cause such a behaviour or require some changes in serial port communications?
Thanks!
****** Update ******************************************************************
Just as update to this: function SetCommState() fails with an error 87 (ERROR_INVALID_PARAMETER). Here it does not matter if I set own parameters, if I use the data received from GetCommState() or if I completely initialise and configure the DCB-structure. So...is this a known bug in SetCommState() of Win 10?
Just to note: it fails only in 4 of 5 cases, so it is not a systematic error, but a random one!
回答1:
Finally: it seems it is a Windows problem, Microsoft has trashed the usbser.sys driver. There are a lot of threads regarding this problem out there:
https://answers.microsoft.com/en-us/windows/forum/windows_10-hardware-winpc/usb-serial-interface-problems-with-windows-10/562943cb-9a65-4900-98ef-03ba453d2742
https://answers.microsoft.com/en-us/insider/forum/insider_wintp-insider_devices/windows-10-serial-usb-problems/438de66f-7294-4c06-b4fb-89b45d005ca0
The second one is the most interesting one: it ends with "we still have the problem" - and then it is closed by MS staff.
I personally found an old Windows 10 installation where usbser.sys worked fine - and after applying all the available Windows patches (including an update of usbser.sys) the problem appeared.
回答2:
We also had problems with ReadFile on COM ports not returning anything while RealTerm worked on the very same ports. As it turned out Windows wasn't properly activated which caused those issues.
来源：https://stackoverflow.com/questions/42203808/accessing-com-port-with-windows-10