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

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

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James Courtier-Dutton wrote:
> Andrey Liakhovets wrote:
>>
>> In short, the attached 1-line patch against alsa 1.0.11 solves the problem
>>
>> If necessary, I can give more details or upload them on our ftp.
>>
>> Andrey Liakhovets
>
>
> Would you be able to provide 2 things?
>
> 1) Please add a "Signed-off-by:" entry.
> 2) Do you have the VT1616A datasheet?
>
> I can find the VT1616 datasheet online, but not the VT1616A.
>
> James

No, I have only the VT1616 datasheet.

Below I repeat the references, info and patch with my Signed-off-by.

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

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.

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

Signed-off-by: Andrey Liakhovets <liakh@dol.ru>

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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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