Re: emu10k1 bug and patch (0.9.0rc7)

[Takashi Iwai <tiwai@suse.de>]

At Mon, 10 Feb 2003 18:21:12 +0100,
Arnaud de Bossoreille de Ribou wrote:
> 
> Hi, I discovered a bug in the emu10k1 driver which I'll explain here:
> 
> I was developing an application which uses the timestamps given in the
> status of the device to send S/PDIF data to it. This app worked pretty
> well except that sometimes I heard sound discontinuities and then a
> constant time delay between the sound and the video.
> 
> I finally found where was the problem, my results is based on the
> emu10k1-debug.patch file attached. The "frame" argument is equal to 0
> when the app gets the status of the device. With this patch applied I
> saw some output on the console exactly at the same time the bug occured.
> Adding a "else" after the "if" to prevent sw_ready from being updated
> fixed the problem and the output looked like
> 
> ----------------
> plop 0 -1536 A B
> plop 0 1536 B A
> ----------------
> 
> where B == A - 1536 (1536 is the period_size). These two lines were
> repeated a few times during playback.
> 
> So the bug looks like a signedness problem since sw_ready is unsigned
> and there is a while(sw_ready > 0), which explain the constant delay,
> next in the "snd_emu10k1_fx8010_playback_transfer" function.

this is because of the incorrect check of boundary-wrap.
the comparison below must be <= instead of <.
(or, it can be simply "diff < 0".)
if there only two periods, the original code cannot detect the
boundary-wrap.

	if (diff) {
==>		if (diff < -(snd_pcm_sframes_t) (runtime->boundary / 2))
			diff += runtime->boundary;
		pcm->sw_ready += diff;
	}

sw_ready should be unsigned safely.
please try the change above with the unsigned sw_ready.


anyway, thanks for your bug report!


ciao,

Takashi


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