[wdmaudiodev] Re: How to avoid prefix number of WDM audio device
- From: Tim Roberts <timr@xxxxxxxxx>
- To: wdmaudiodev@xxxxxxxxxxxxx
- Date: Mon, 15 Oct 2018 10:22:11 -0700
K. Weller wrote:
Well the audio device is already out so this seems to be a good
solution avoiding this in future and now, the reason is clear to me !
I just found this "HACK" to let Windows ignore the serial number:
If this works it seem to be a solution for now I guess.
You need to read this again, because this does exactly the opposite of
what you need.
Here's the problem. If your device has a serial number, then Windows
can uniquely identify that physical piece of hardware, no matter where
it is plugged in. It only creates one devnode, one driver install, and
one set of configuration data. But if your device does not have a
serial number, Windows cannot uniquely identify it. Thus, when it sees
your VID and PID in a different hub or port for the first time, it has
to assume it is a new device. It creates a new devnode, does a new
install, and creates a new set of configuration data. If it did not do
that, and you plugged in two devices into two different ports, the two
would collide. That's not allowed.
The web page you quote above tells Windows to ignore a serial number if
it is present, so that it creates a new devnode for each new hub/port.
That's the opposite of what you want. That option is designed for
manufacturing floors, where you might plug 10,000 devices into a single
port. If they all had serial numbers, that would create 10,000 new
devnodes and fill your registry. With that registry hack, it would only
create one that gets reused each time.
The USB specification strongly recommends that each device have a unique
serial number, and some of the device classes require it. However,
manufacturers are lazy. It's not easy to give each device a unique
serial number, so they don't, and that causes problems like this.
Tim Roberts, timr@xxxxxxxxx
Providenza & Boekelheide, Inc.
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