[alsa-devel] [PATCH] ASoC: WM9712 Codec: Workaround an unmute problem (Was: Re: [PATCH] ASoC: MPC5200: Support for buffer wrap around)

[Jon Smirl]

On Wed, Aug 5, 2009 at 1:16 PM, Jon Smirl<jonsmirl at gmail.com> wrote:
> On Wed, Aug 5, 2009 at 12:30 PM, John Bonesio<bones at secretlab.ca> wrote:
>> Hi Mark,
>>
>> I've retitled the email to better reflect the real patch. I believe
>> there has been some general confusion because I originally sent the
>> wrong patch.
>>
>> You wrote:
>>
>>> Like I said before, exactly which control are you adjusting here?
>>>
>> My description of this got lost in all the confusion. Let me try again.
>> We are adjusting the mixer bits for mute/unmute on two of the mixer
>> settings. The first one is general headphone mute setting on register
>> 0x4 (bit 15). The second one is the PCM mute setting on register 0x18
>> (bit 15).
>>
>> What we are seeing is that if we first unmute the general headphone (reg
>> 0x4 bit15), then unmute the PCM (reg 0x18 bit 15) [HPL PCM in the
>> alsamixer application], the general headphone gets muted again, even
>> though software didn't write to that register.
>>
>>>
>>> > If there is code in software doing this, it's very subtle.
>>>
>>> My money would be on the AC97 controller having problems; the quality of
>>> SoC AC97 controllers is variable.  It certainly doesn't sound like a
>>> WM9712 issue; as I say I'd be very surprised if such an issue hadn't
>>> come up before given how widely deployed the part is.
>>
>> We don't have access to an AC97 analyzer. Do you have any suggestions on
>> other ways we can pinpoint the error?
>
> Do you have a normal logic analyzer? You can decode the AC97 by hand,
> its only a couple of frames.

My hardware engineer has this one, but it is in Seattle and I am in
Florida. The OpenMoko guys use it.
http://www.pctestinstruments.com/

You can write your own interpreters, someone may have done AC97 for it
but I haven't checked.

He also has a Rigol DS1102E which he says is an awesome scope for
$636. Another tip from OpenMoku.
http://www.tequipment.net/RigolDS1102E.html


-- 
Jon Smirl
jonsmirl at gmail.com