[wdmaudiodev] Re: Kernel streaming question
- From: Pallavi Joshi <pallavi.v.joshi@xxxxxxxxx>
- To: wdmaudiodev@xxxxxxxxxxxxx
- Date: Wed, 24 Jun 2009 13:49:02 -0700
Okay I will try to implement that. Will let you know how it goes.
Thanks very much for your help.
Pallavi
On Wed, Jun 24, 2009 at 11:29 AM, Tim Roberts <timr@xxxxxxxxx> wrote:
> Pallavi Joshi wrote:
> > Yes, it makes sense. I measured the time it takes for my function to
> > input data(256 samples). It takes around 16 ms whereas it should be
> > taking like ~6 ms. I do not know why that is the case. This is only
> > true with USB. With the laptop's default audio card it takes ~6 ms.
> >
> > The data comes from the USB's audio capture pin. I have connected a
> > MP3 player to the stereo input of my USB audio device....that's where
> > the input data comes from.
> >
> > May be the input takes more time because USB operation is slow...is
> > that a possibility?
>
> 16ms sounds suspiciously like you are waiting to be rescheduled.
>
> Again, remember that this is a real-time path. There is no buffering.
> If you ask for 256 samples (1024 bytes, right?), your request gets sent
> down the stack, the buffer is filled and returned, but nothing else can
> happen until you send down a new buffer. During the time between your
> request being filled and you shipping an empty buffer back down, audio
> data is being lost.
>
> You need to have several buffers going at once. That is, submit 3 or 4
> read requests all at once. As each is returned, you can process it and
> return it, but while you are playing around, your next buffer is being
> filled.
>
> --
> Tim Roberts, timr@xxxxxxxxx
> Providenza & Boekelheide, Inc.
>
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--
Pallavi Joshi
(480)-280-2017
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