Hi, 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 while (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 toggling a printer port pin. When I play audio with the Windows Media Player using the same driver (without reloading) 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 kernel 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 software. Do I missing something obvious? Best regards, Bart ****************** WDMAUDIODEV addresses: Post message: mailto:wdmaudiodev@xxxxxxxxxxxxx Subscribe: mailto:wdmaudiodev-request@xxxxxxxxxxxxx?subject=subscribe Unsubscribe: mailto:wdmaudiodev-request@xxxxxxxxxxxxx?subject=unsubscribe Moderator: mailto:wdmaudiodev-moderators@xxxxxxxxxxxxx URL to WDMAUDIODEV page: http://www.wdmaudiodev.de/