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Subject: 1.57 on Win2k or WinXP. Not more than 16 com ports. Differences between //./comX and /dev/comX
Date: Mon, 19 Apr 2004 18:29:22 +0200
Message-ID: <C2F0FC2A5C4B3E44ADF4327E699486A509F528@mail2.de.thorlabs.local>
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From: =?iso-8859-1?Q?Lutz_H=F6rl?= <lhoerl AT thorlabs DOT com>
To: <cygwin AT cygwin DOT com>
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Hello,

I want to use (Windows-) COM port numbers greater
than 16, but when I use open() to get a file
descriptor for the devices I get the behaviour:

---1.case-----------------------------------------

errno = 0;
fd = open("/dev/com8", O_RDWR | O_NONBLOCK);
-> fd = 3, errno = 0
-> everything is OK,
   I can use the opened COM port

---2.case-----------------------------------------

errno = 0;
fd = open("\\.\com8", O_RDWR | O_NONBLOCK);

-> fd = 3, errno = 20 = ERROR_BAD_UNIT
   = "The system cannot find the device specified"
-> I can not use the opened COM port. The port
   number 1...16 versus 17...255 does NOT matter.

---3.case-----------------------------------------

errno = 0;
fd = open("/dev/com23", O_RDWR | O_NONBLOCK);

-> fd = -1, errno = 2 = ERROR_FILE_NOT_FOUND
   = "The system cannot find the file specified"
-> I can not use the opened COM port. The port
   number 1...16 (OK) 17...255 (not OK) DOES matter.

---end cases------------------------------------

Is there a workaround?

Lutz Hoerl

Thorlabs GmbH
Gauss-Strasse 11
D-85757 Karlsfeld
Germany

Tel.    +49 (0)8131 5956 44
FAX     +49 (0)8131 5956 99
M A I L    lhoerl at thorlabs dot com

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