[Discuss] Generic USB devices

[bogstad at pobox.com (Bill Bogstad)]

On Fri, Jun 9, 2023 at 8:03?PM <markw at mohawksoft.com> wrote:

>
> LOL, there is no real difference. Doing a diff found this:
>
>......
>
> Yes, of course, you could visually inspect and find some arcane difference
> between two devices, but that isn't the point. The usb system supplies a
> vendor/product ID so that "plug & play" works, however, when that "plug &
> play" mechanism only presents you with a generic serial device, it is
> broken.

If there was an actual RS232 serial cable between a USB-serial
converter and your device, you wouldn't expect to know what was
connected on the other end of the cable from the USB side.   In the
old days, there would have been an explicit port name for each serial
port and you would have to explicitly select it in the software
/dev/ttya, ttyb, whatever.

Unfortunately, USB doesn't apparently give you a way to determine
which physical port is being used by a device.   You might have a
similar problem if you connected two identical models of storage or
network devices via USB.  Playing around a bit with USB devices on my
system, it seems that devices have serial numbers (iSerial) which
might help if implemented correctly.  (On my system however, I have
several USB devices which clearly do not.)   Whoever built your two
devices, probably took pre-existing designs for RS232 devices, slapped
a cheap USB-serial chip in the box and now claim "we support USB".  In
the best case, you might hope that whoever wrote
the MS Windows drivers/software to talk to their device did something
more than look for the first USB-serial adapter and actually verify it
is their device; but it wouldn't surprise me if they didn't.   Your
case is just not worth the engineering effort in the modern world.
Just the price of cheap technology...

Bill Bogstad