[Nut-upsuser] Re: [Nut-upsdev] megatec driver and usb-to-serial converters

Charles Lepple clepple at gmail.com
Fri Nov 3 04:51:21 CET 2006

On 11/2/06, Carlos Rodrigues <carlos.efr at mail.telepac.pt> wrote:
> On 11/2/06, Doug Reynolds <mav at wastegate.net> wrote:
> > I not sure if this helps, but Windows XP automatically supports serial
> > to USB cables without installing any additional drivers..  There is
> > probably some kind of spec...  good luck finding it though.
> AFAIK, both Windows and Linux have a similar level of support for
> these devices

To add some acronyms to the discussion:

There is a USB Communications Device Class (CDC) which encompasses
both ethernet-like adapters as well as RS-232-type devices (Abstract
Control Model, or CDC ACM). If the device has a proper CDC ACM
descriptor, then both Linux and Windows should recognize the device
regardless of its VID/PID. Here's the matching code for Linux:

   http://lxr.linux.no/source/drivers/usb/class/cdc-acm.c#L1071 (as of

Regarding Peter's comment, I'm not sure that the USB forum discourages
USB-to-serial. I gather that it's just a complex spec, and most people
want something easy to use, and under Windows, something that doesn't
require driver-level hacking (hence, USB-to-serial-over-HID).

> in both cases there are a set of them which have their
> IDs already listed, there are others that aren't recognized because
> their IDs are not yet listed, and there are others yet which really
> need special drivers/hardware specific hacks.

This is the less standardized class of devices, and it is not easy to
identify them programmatically. Most of them are covered by the
usbserial driver in Linux.

- Charles Lepple

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