Re: [hatari-devel] Sound sync patch to play with

[David Savinkoff <dsavnkff@xxxxxxxxx>]

On Sunday 13 May 2012 14:13, Nicolas Pomarède wrote:
> On 13/05/2012 20:37, David Savinkoff wrote:
> > Hi,
> >
> > Here is a patch for synchronizing Hatari to sound.
> > A check box in in the SDL GUI is provided to
> > enable or disable synchronization.
> >
> > Documentation and comments are in the patch.
> > Give it a try. It should make things better if
> > there is a problem, and make little difference
> > otherwise.
> >
> > ps. I'm resending this because I hope to have it in
> > the upcoming hatari release.
> >
> > Thanks,
> > David
>
> Hello, I didn't have time to test this yet. I will try to have a look
> (but other people opinion is also welcomed).
>
> But at the base, I'm not sure I can really test this, I rarely
> experience such latency problems.
>
> If you have this often, couldn't it be due to a not enough powerful cpu
> or bad audio driver for your specific audio hardware ?
>
> Nicolas

Hi Nicolas,

I believe the latency is caused when a sound card does not consume
the samples as fast as the computer provides them. This causes the
buffers to eventually fill to the maximum before samples are discarded.

A slow cpu will result in no latency, whereas a fast cpu could cause
latency. My sound card is slower than the computer, and your sound
card is faster (no sound card is the same speed as the computer).

The fundamental problem is that the sound card's timing is independent
from the other timers. SDL_GetTicks is flawed in that it uses the PIT timer..
It should use vsync for the video time-base, and the SDL_audio_callback
for the sound time-base.

The patch addresses the fundamental problem by using the SDL audio
callback to smoothly micro-throttle Hatari. Jitter caused by Multitasking
in Linux is addressed by the sound buffer.

I tested this patch with:
hatari --sound-buffer-size 10
Also 5, 20, 30, 40 and others ( I modified sources to get 5 ).

David