[wdmaudiodev] Re: wdmaudiodev Digest V1 #128

  • From: Ben Allison <benjamin.james.allison@xxxxxxxxx>
  • To: wdmaudiodev@xxxxxxxxxxxxx
  • Date: Wed, 24 Nov 2004 12:07:24 -0500

Windows XP (and previous versions) have difficulties dealing with two
identical USB devices.

Please see this semi-technical discussion at one of the Windows
developer's blogs.
http://weblogs.asp.net/oldnewthing/archive/2004/11/10/255047.aspx

-Ben Allison

> From: "Bert Schiettecatte" <bert@xxxxxxxxxxxx>
> Subject: [wdmaudiodev] Re: USB midi driver?
> Date: Wed, 24 Nov 2004 00:47:28 +0100
> 
> Hi,
> 
> Actually, it does.  Every system exclusive message has a manufacturer's
> identification code.  An app that knew it was getting multiple devices
> on separate MIDI controllers could distinguish them by using that.
> 
> That won't work. There is no way you can tell the difference between two
> control messages being sent. You can't tell from which device the
> message is sent because they look identical, apart from the control
> value. System exclusive is only used to transfer device configuration
> settings, etc. Of course you can use sysex to send a unique serial
> number, but that's really a dirty hack. I would rather have Win XP
> assign unique names to both devices, e.g. :
> 
> midi devices
> |- midi controller #1
> |- midi controller #2
> 
> The question in my mind is this:  what do you mean by "distinguish"
> them?  Windows will certainly let you plug in two identical devices, it
> will load drivers for the two devices, and it will expose interfaces for
> both devices.  An application that enumerates all the MIDI devices will
> find two of them, with different device IDs.  If the app KNOWS there
> will be two different devices, it can open one instance to each.
> 
> I am not sure Win XP will allow you to connect 2 identical devices or it
> will support 2 of these devices at the same time. Even if it allows you
> to do that, it will assign identical names (and different IDs like you
> said) to the devices. Which might confuse MIDI software that was not
> properly designed and uses names to distinguish between devices.
> 
> How would you EXPECT to be able to distinguish them?  Describe for me a
> use case in which this is important, and how you visualize things
> working.
> 
> suppose somebody buys two identical midi devices. he arrives home, knows
> what he is doing, installs the drivers first, then plugs in both
> devices. suppose he is lucky and Win XP shows 2 new midi devices with
> identical names in the hardware list (control panel/system).
> next he starts his favorite MIDI application which lists 2 identical
> midi devices. no way to tell which physical device corresponds to which
> name in the combo box! now, there is no way for the user to know where
> he is sending his controller messages each time he has to select the
> device in some combo list (and this happens many times in pro audio
> applications). so he has to use trial and error each time he needs to
> select the right device from some list, to find the device he actually
> wants to send data to. now, imagine he buys 4 of these identical
> devices, can you imagine how cumbersome this becomes?
> 
> bert
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