[wdmaudiodev] Re: Bug in usbaudio.sys (XP SP1 as well as SP2) MIDI support
- From: Tim Roberts <timr@xxxxxxxxx>
- To: wdmaudiodev@xxxxxxxxxxxxx
- Date: Mon, 22 Nov 2004 09:05:42 -0800
BlazeAudio Developer wrote:
We have found a rather significant bug in USBAUDIO.SYS that involves
USB MIDI support.
The problem is that if a lower filter is attached (below
usbaudio.sys), then sysaudio fails to create the CATEGORY_AUDIO_DEVICE
filters. And the reason sysaudio fails is that the pins created by
usbaudio for MIDI cannot not provide a proper pin name.
After about three days of debugging, and stepping through a fair
amount of usbaudio and sysaudio code, we have found the reason for this.
The reason is that Usbaudio.sys tries to obtain the device description
of the PDO that it is working on using IoGetDeviceProperty() with
DevicePropertyDeviceDescription.
If there is no lower-filter for usabaudio, then this works fine.
However, if there is a lower-filter present, then usbaudio is actually
trying to make this call on the Filter Device Object (FiDO) that it
thinks is the PDO.
That's interesting, because there was an almost identical bug in the
Win98 Gold version of STREAM.SYS. It tried to open the registry key for
the next driver down to read naming information, but it used the FiDO
instead of the PDO. The bug made it impossible to use a lower filter
with any stream-class driver, including USBAUDIO.SYS.
We actually shipped three drivers which patched STREAM.SYS on the fly
for this problem.
--
- Tim Roberts, timr@xxxxxxxxx
Providenza & Boekelheide, Inc.
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