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1.57 on Win2k or WinXP. Not more than 16 com ports. Differences between //./comX and /dev/comX
- From: Lutz Hörl <lhoerl at thorlabs dot com>
- To: <cygwin at cygwin dot com>
- Date: Mon, 19 Apr 2004 18:29:22 +0200
- Subject: 1.57 on Win2k or WinXP. Not more than 16 com ports. Differences between //./comX and /dev/comX
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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