Re: SetCommState() fails with "A device attached to the system is not functioning"

Tech-Archive recommends: Repair Windows Errors & Optimize Windows Performance

"Joseph M. Newcomer" <newcomer@xxxxxxxxxxxx> wrote in message
news:lfbcr35657sg92467bd6gte0gq4v6a0ieh@xxxxxxxxxx
My suspicion would be that the virtual control does not successfully
implement all the
IOCTL codes required. There are something like 40 IOCTLs that a serial
port must support.
If it would fail to support one of these, the consequence would probably
be the error you
are seeing.

It sounds like the fix is not in SetCommState, but in the device driver
for the virtual
device.

Short of exploring the DDK documentation in detail, to see what IOCTL is
failing, I don't
have any effective way to isolate the failure. Note that SetCommState is
nothing more
than a high-level wrapper around a set of DeviceIoControl calls.

I'd suggest downloading the file monitor from www.sysinternals.com and
study what IOCTLs
are being sent to your device (look for IRP_MJ_DEVICE_CONTROL requests)
and which one is
failing.

Thanks, Joe. The driver is the standard usbser.sys (USB serial port driver
that Windows provides). But the firmware on the device may be suspect. I
just got a new build of the firmware and will let you know if it fixes the
problem.

Thanks,
David


.

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