1.57 on Win2k or WinXP. Not more than 16 com ports. Differences between //./comX and /dev/comX

Mon Apr 19 17:54:00 GMT 2004

At 12:29 PM 4/19/2004, you wrote:
>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);

 ^^^^^^^^^
You didn't escape the backslashes. "//./com8" should work too.
>-> 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.

Right. Cygwin only maps the first 16 com ports to this
POSIX syntax. The Win32 syntax as amended above should
work for you though.
--
Larry Hall http://www.rfk.com
RFK Partners, Inc. (508) 893-9779 - RFK Office
838 Washington Street (508) 893-9889 - FAX
Holliston, MA 01746 
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