Re: [Openchrome-users] via epia boards sound quality

["Andrey Liakhovets" <liakh@dol.ru>]

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This letter is continuation of the thread in Openchrome-users:
http://wiki.openchrome.org/pipermail/openchrome-users/2006-May/001193.html
http://wiki.openchrome.org/pipermail/openchrome-users/2006-May/001199.html
http://wiki.openchrome.org/pipermail/openchrome-users/2006-May/001247.html
http://wiki.openchrome.org/pipermail/openchrome-users/2006-July/001456.html

I am sorry for continuing this thread but there is good news.

In short, the attached 1-line patch against alsa 1.0.11 solves the problem
(for our VIA EPIA SP8000).

Further details:
1) in our lab, we failed in getting bad sound on a running system,
       despite a long and intensive heating;
2) we have succeded in reproducing the problem at the system start (with a
       probability of about 2/3) with a pre-cooled sound codec chip;
3) we have succeded in reproducing the problem on the system running Linux
       by cutting analog power supply from the codec, cooling the codec and
       reattaching analog power;
4) on wire, the problem looks like undervoltage of codec analog power
       (2V or less instead of 5V): meanwhile the codec tries to consume
       about 200mA (instead of <40mA), and the voltage regulator chip begins
       (from 100mA) reducing the voltage;
5) analysis of the situation with WinXP shows that the WinXP sound driver loading
       brings the codec analog voltage (and sound) to norm, and this state
       is tolerant to actions described under (3);
6) analysis of the WinXP sound driver loading allowed us to detect that very bit,
       the set of which normalizes the codec's analog power consumption;
7) a check with Linux has confirmed this.

If necessary, I can give more details or upload them on our ftp.

Andrey Liakhovets

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diff -Naur a/pci/ac97/ac97_patch.c b/pci/ac97/ac97_patch.c
--- a/pci/ac97/ac97_patch.c	2006-04-12 00:46:47 +0400
+++ b/pci/ac97/ac97_patch.c	2006-07-26 10:15:58 +0400
@@ -2742,6 +2742,7 @@
  */
 int patch_vt1617a(struct snd_ac97 * ac97)
 {
+	snd_ac97_write_cache(ac97, 0x5c, 0x20);	/* bring analog power consumption to normal, like WinXP driver for EPIA SP */
 	ac97->ext_id |= AC97_EI_SPDIF;	/* force the detection of spdif */
 	ac97->rates[AC97_RATES_SPDIF] = SNDRV_PCM_RATE_44100 | SNDRV_PCM_RATE_48000;
 	return 0;




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