[wdmaudiodev] Re: HD Audio WaveCyclic timing problems

  • From: Mike Pumford <mpumford@xxxxxxxxxxxxxx>
  • To: wdmaudiodev@xxxxxxxxxxxxx
  • Date: Tue, 12 Jan 2010 09:36:15 +0000

Lex Nahumury wrote:
This is my first post here and I hope some of you fine people can help
me out here.

I'm developing a HD Audio function driver targeting WIN XP SP3.
Everything so far works fine but I can't get the stream's position timing right.
That is, although the playback rate sounds ok, the rendered sound is
always garbled and I can't seem to find the solution.

Here is what I do;
Based on the "Microsoft Device Driver Interface for HD Audio" documentation I
use WaveCyclic and obtain a HDAUDIO_BUS_INTERFACE_BDL from the HD Audio DDI.
Since the function driver doesn't have a physical DMA object itself,
my stream class inherits from IDmaChannel and implements the
IMP_IDmaChannel member functions. (pretty much how it is done in the
MSVAD sample)

At pin creation time I do AllocateRenderDmaEngine() followed by
AllocateContiguousDmaBuffer() to create a PAGE_SIZE sized buffer.

That might be too small. I found I needed a larger buffer than this for playback/record operations involving high sample rates, sample widths and number of channels. In the end I ended up computing a size relative to nAvgBytesPerSec.

In SetNotificationFreq() I compute the needed 10msec FramingSize,
   FramingSize_in_bytes = nBlockAlign * sampleRate * Interval / 1000;

I use that FramingSize;
- to set the current buffersize via SetBufferSize(FramingSize_in_bytes)
- to program the length of the first (and only) BDL entry
- and in the call to SetupDmaEngineWithBdl() with LVI = 1

In GetPosition() I readout the address I obtained earlier via

   *Position = READ_REGISTER_ULONG( pPositionRegister )

That's not quite right for a HD audio device (at least in my experience). For GetPosition you need the position of the current sample actually being played or recorded. To do this for HD Audio you need to to adjust the link position register value using the FifoSize (you can get this from the HD Audio interface). For Capture streams return LinkPosition - FifoSize, for render streams return LinkPosition + FifoSize. Return 0 if the stream is stopped.

Mike Pumford, Senior Software Engineer
MPC Data Limited
e-mail: mpumford@xxxxxxxxxxxxxx     web: www.mpc-data.co.uk
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