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Re: Looking for basic documentation on Cygwin and Serial Ports

On 4/24/08, Nefastor <> wrote:
> Brian Dessent wrote:
> >
> > Nefastor wrote:
> >
> >> (...) I don't know which of Cygwin's /dev/tty device corresponds to which
> >> serial
> >> port on my PC (that is, I only know the COM port number). I can "sort of
> >> guess" /dev/tty0 is COM1, but that's a guess, and I'd prefer some
> >> certainty.
> >
> > Cygwin works the same as Linux, /dev/ttyS0 is the first serial device,
> > /dev/ttyS1 is the second, etc.  Please consult the users guide:
> > <>.
> >
> >
> That I have, Brian. What itches me is that I'm facing some kind of special
> case : My machine has two serial port, one on the MoBo and a USB-serial
> adapter, yet Windows calls them COM1 and COM3. I've searched the whole
> Device Manager but couldn't find any device that would be COM2. And I can
> rename COM1 to COM2.
> Speaking of Windows' DM, it's rather quirky on the serial ports : I noticed
> that if I unplug my USB cable (COM3) and try to change the name of COM1, in
> the drop down box COM3 is listed as "in use" :confused: %-|.
> So, I have a machine with two serial ports but no COM2, AND I can change the
> COM port number to whatever I want, plus Windows seems to have a bad case of
> "phantom limb syndrome". Getting back to your answer : how can know for sure
> what Cygwin calls "the first port", or "the second port" ?
> Trial and error is obviously not what I'm after, rather I need a way for my
> program to know for sure what port it's dealing with. To help me write that
> program I'd need to know :
> - is there a fixed relationship between COM port number "X" and dev/ttyS
> number "Y", such as Y = X - 1 ? For instance, if I change my COM port number
> from 3 to 7, will the dev/ttyS number go from 2 to 6, or will it remain
> unchanged ?
> - if it remains unchanged, I'm assuming Cygwin does some sort of port
> enumeration : is that process deterministic ?
> Additionally, can you point me to documentation on how to retrieve device /
> driver info from my program ? That way, worst case scenario, I can have the
> program look for the correct port on its own.
> Thank you for your time, I know I'm asking for a lot of stuff but I've got
> the feeling the answers would be useful to many.:-)

What motherboard do you have?  It's always possible that there is a
riser pinout for a serial port somewhere in the front of the board for
connection to a front panel mount.

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