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Date: Thu, 24 Apr 2008 15:08:03 -0700 (PDT)
From: Nefastor <nefastor AT hotmail DOT com>
To: cygwin AT cygwin DOT com
Subject: Re: Looking for basic documentation on Cygwin and Serial Ports
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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:
> <http://cygwin.com/cygwin-ug-net/using-specialnames.html>.
> 
> 

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.:-)

Nefastor
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