dummy problems

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dummy problems

Ian Gulliver-2
The dummy driver currently has timing issues: it attempts to time using
relative hops between each callback, not counting the time taken in the
callback and piling up rounding error.  The effect becomes more
prominent the more times the callback happens (longer real time period,
higher sample rate or less frames per period).

Attached is a patch to switch to an absolute time calculation.  It also
adds some math for a virtual "buffer" inside the driver, and warnings if
we would have skipped with that buffer setting (i.e. if your machine
can't keep up).

On my machine, a 38 second playback through JACK with the old driver
took 44 seconds at 96000 samples/sec; with this patch, it takes exactly
38.

--
Ian Gulliver
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Re: dummy problems

Ian Gulliver-2
> Subject: [Jackit-devel] dummy problems

Sorry for the noise; patch attached this time.

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Re: dummy problems

Lee Revell
In reply to this post by Ian Gulliver-2
On Wed, 2006-06-28 at 16:44 -0400, Ian Gulliver wrote:
> The dummy driver currently has timing issues: it attempts to time using
> relative hops between each callback, not counting the time taken in the
> callback and piling up rounding error.  The effect becomes more
> prominent the more times the callback happens (longer real time period,
> higher sample rate or less frames per period).
>
> Attached is a patch to switch to an absolute time calculation.

-ENOPATCH


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Re: dummy problems

Jack O'Quin
In reply to this post by Ian Gulliver-2
On 6/28/06, Ian Gulliver <[hidden email]> wrote:
> > Subject: [Jackit-devel] dummy problems
>
> Sorry for the noise; patch attached this time.

What does PRETEND_BUFFER_SIZE represent?

Why is it different from driver->period_size?
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Re: dummy problems

Ian Gulliver-2
> What does PRETEND_BUFFER_SIZE represent?
>
> Why is it different from driver->period_size?

It's the size, in samples, of the dummy devices "hardware" buffer
(pretend, because there's no actual hardware).  This is used to
determine when it prints warnings, by calculating when it actually would
have skipped, had there been a real device there.

--
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Re: dummy problems

Jack O'Quin
On 6/30/06, Ian Gulliver <[hidden email]> wrote:
> > What does PRETEND_BUFFER_SIZE represent?
> >
> > Why is it different from driver->period_size?
>
> It's the size, in samples, of the dummy devices "hardware" buffer
> (pretend, because there's no actual hardware).  This is used to
> determine when it prints warnings, by calculating when it actually would
> have skipped, had there been a real device there.

OK.  This patch seems to work well for me.  Unless someone objects,
I plan to commit it soon.
--
 joq

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Re: dummy problems

Jack O'Quin
On 6/30/06, Jack O'Quin <[hidden email]> wrote:

> On 6/30/06, Ian Gulliver <[hidden email]> wrote:
> > > What does PRETEND_BUFFER_SIZE represent?
> > >
> > > Why is it different from driver->period_size?
> >
> > It's the size, in samples, of the dummy devices "hardware" buffer
> > (pretend, because there's no actual hardware).  This is used to
> > determine when it prints warnings, by calculating when it actually would
> > have skipped, had there been a real device there.
>
> OK.  This patch seems to work well for me.  Unless someone objects,
> I plan to commit it soon.

Committed to SVN, version 0.102.19, rev 980.

Thanks for the patch, Ian.
--
 joq

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