[wdmaudiodev] MediaPlayer improves USB DPC timing

  • From: "bart@xxxxxxxxxxxxx" <bart@xxxxxxxxxxxxx>
  • To: WDM list <wdmaudiodev@xxxxxxxxxxxxx>
  • Date: Fri, 25 Jul 2003 09:56:44 +0200


I observed a very strange effect on a USB (sound) device I am developping. In 
my driver
the URB/IRP pairs are recycled in the completion routine evey 3 msec. Once in a 
(aprox 10 seconds) the completion routine is not called for more as 12 msec 
causing data
underrun when I play audio using MME with WaveLab (XP sp1). I measured this by 
a printer port pin.

When I play audio with the Windows Media Player using the same driver (without 
this problem does not appear. When I stop the Media Player (not exit it) and 
then play
with WaveLab the problem also is gone. When I then play using the ASIO driver 
with WaveLab
the problem still stays away. Then when I exit the Media Player the problem 
immediatly comes
back again. This effect is repeatable, as soon as the Media Player has played a 
bit the
timing behaviour of the (at least USB involved) DPC's improves dramaticly.

The only conclusion I can draw from this that the Media Player switches the XP 
to a 'realtime mode' such that the DPC timing improves. Is this a known 
'feature'? I don't
want to suggest this is a way MS makes its software better perform as 3d party 
Do I missing something obvious?

Best regards,

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