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Re: Problem opening new serial ports


On 2008-08-05, Gary Johnson wrote:
> I've been successfully using the original two serial ports on my
> Windows PC, COM1 and COM2, referring to them to Cygwin tools as
> /dev/ttyS0 and /dev/ttyS1, respectively.  I needed two more serial
> ports, so I used a device that plugs into a USB port on a PC and
> provides two serial ports.  The device is an Edgeport/2 USB
> Converter.  I installed the drivers and now the Windows Device
> Manager shows the following under "Ports (COM & LPT)":
> 
>    Communications Port (COM1)
>    Communications Port (COM2)
>    EdgePort [V20853020-0] Serial Port - 1 (COM24)
>    EdgePort [V20853020-0] Serial Port - 2 (COM25)
> 
> plus devices on LPT1, COM4 and COM5.
> 
> Cygwin tools don't seem to be able to find these two new ports.  For
> example:
> 
>    $ stty < /dev/ttyS23
>    bash: /dev/ttyS23: No such file or directory
> 
>    $ stty < /dev/ttyS24
>    bash: /dev/ttyS24: No such file or directory
> 
> Is there something else I need to do to get Cygwin to recognize
> these ports?  Do they look like serial ports to Cygwin, or does
> Cygwin see only the USB port?
> 
> I have not rebooted the machine since installing the EdgePort device
> since I have experiments running on it at the moment.

OK, I did some Googling and found a "Cygwin USB-to-Serial HOWTO" 
(http://tmp.ua964.com/cygwin-usb-to-serial-howto/) and a thread in 
this list from May, both mentioning Cygwin's limit of 16 com ports.  
They also say that this is in the FAQ, but I sure couldn't find it 
there.  So it looks like my choices are:

1.  Wait for 1.7 (I'm currently using 1.5.25(0.156/4/2).
2.  Build my own cygwin1.dll and change the limit to 64.
3.  Rename COM24 and COM25 to 16 or below.

I tried #3, but the drop-down list of COM ports says ports COM1 - 
COM23 are "(in use)", yet only COM1, COM2, COM4, COM5, COM24 and  
COM25 are in the Device Manager List.  The other ports were probably 
taken by various USB devices I've plugged in at one time or another 
but am no longer using.

There seems to be no way to simply and safely remove a COM port 
without first removing the driver that owns it, and no way that I've 
found to find what driver owns a particular COM port.  This is 
getting OT, though.  It looks like #2 is my best bet.

Regards,
Gary


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