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My hardware enumerates as COM125 on the device manager (CDC-ACM class). But, I can't find it under /dev/tty* listing. Does cygwin have a limitation on CDC-ACM class of com ports or numbers greater than 100? I have few other UARTs (emulated over USB) that enumerate as COM10COM20 range. These are listed as /dev/ttyS9 and etc in cygwin.

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Does cygwin have a limitation on CDC-ACM class of com ports or numbers greater than 100?

Actually, the limit appears to be 64. There is a hard-coded table in winsup/cygwin/devices.cc within the Cygwin source code which has 64 entries for /dev/ttyS*. (It starts on line 732 in the current version.)

Since Windows itself copes with higher-numbered devices, this is likely to be an arbitrary choice (i.e. "Who would need more than 64 serial devices?") rather than some difficult-to-overcome limit in Cygwin or Windows. Therefore, I recommend that you check out a copy of the Cygwin sources, extend that table, and then build your own cygwin1.dll.

(I could do so myself, but since I lack a device that appears so far up there in COM space, I couldn't test the patch.)

If that succeeds, they will welcome your report on the main mailing list.

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  • Thank you. Sorry, I don't have this setup any more. Will make a point to file a patch next time.
    – tecMav
    Sep 24, 2016 at 14:19

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