[wdmaudiodev] Re: Problem about GetMapping() / ReleaseMapping() in WavePCI
- From: Ken Cooper <Ken.Cooper@xxxxxxxxxxxxx>
- To: "wdmaudiodev@xxxxxxxxxxxxx" <wdmaudiodev@xxxxxxxxxxxxx>
- Date: Mon, 20 Oct 2008 11:28:20 -0700
There should be no difference in audio quality between WaveCyclic and WavePci.
If you are having issues with WaveCyclic, then you are likely doing something
wrong in your driver. The IRP handling between the two models is essentially
the same, with the main difference that in the case of WavePci we hand you the
page mappings from the mapped IRP buffer and in WaveCyclic we copy the data
from the IRP buffer into your cyclic buffer based on your indication of DMA
position with a DPC that is scheduled whenever you notify us.
We originally wrote WaveCyclic to support the legacy DMA controllers of the day
(circa 1997) that couldn't do scatter-gather. The cost being that a data copy
was needed between the IRP buffer written by the application and the DMA buffer
accessible to the hardware. WavePci was written to eliminate the need for the
data copy for DMA controllers that could support scatter-gather. While we
saved CPU with the elimination of the data copy, we added overhead with all of
the mapping management.
If you are looking to support Vista/Win7 and don't care about back-porting to
XP, you can use the WaveRT model that we introduced in Vista. In this model
the hardware DMA buffer is mapped directly into the application's usermode
process space and there is no streaming IRP flow at all. The application
writes directly into the DMA buffer based on the DMA position (that it can read
either from a memory-mapped register or using the traditional property
technique).
Best Regards,
Ken
From: wdmaudiodev-bounce@xxxxxxxxxxxxx
[mailto:wdmaudiodev-bounce@xxxxxxxxxxxxx] On Behalf Of pritesh gajjar
Sent: Saturday, October 18, 2008 12:10 AM
To: wdmaudiodev@xxxxxxxxxxxxx
Subject: [wdmaudiodev] Re: Problem about GetMapping() / ReleaseMapping() in
WavePCI
Hi Devendra,
audio quality is not really good in waveCyclic miniport driver
What makes you think so?
My conjecture is that the IRP handling and queueing is done by portcls in our
buffer, whose address we give to PortCls through SystemAddress(). So it may due
to overrunning of read pointer in buffer. Due to which buffer gets emptied and
waits for new IRPs to get write pointer move ahead, then everything moves
smoothly for few seconds. Same thing repeated again. Since that read /write
pointer is not in our hand, we can not much about it. That's where WavePCI has
advantage over WaveCyclic.
--
Thanks and regards
Pritesh
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