[alsa-devel] [PATCH 1/1] ASoC: TWL4030: Headset VMID ramp fix

[Peter Ujfalusi]

On Friday 08 May 2009 09:40:44 ext Jarkko Nikula wrote:
> It really does fix the power-up & -down pops on Beagle. By listening
> carefully I can hear slight power-up and -down pops but only if really
> focusing on it.
>
> But now the audio output is distorted and volume level is a little bit
> lower. Without the patch it plays fine. Is it possible that now the
> output voltage is not correctly biased? Worth to check with a scope.

Well, that's what you get, when you are testing audio with /dev/zero and 
/dev/urandom... I have not noticed that the random noise got more random ;)
What you have described is correct, it is heavily distorted.

But I have debugged this further and I believe I know what is going on:
The sequence for disable according to the documentation:
HS_POP_SET:RAMP_EN = 0
HS_POP_GAIN:HSL_GAIN, HSR_GAIN = 0
HS_POP_SET:VMID_EN = 0

Now what is missing from this is that after setting the HS_POP_SET:RAMP_EN = 0 
it will take RAMP_DELAY time for the VMID to reach 0.
Since we are not waiting between RAMP_EN = 0 and VMID_EN = 0, the VMID has 
been cut, which causes the 'tuck' on the headset output.

In case of the Beagle board the ramp delay can be configured(MCLK=26MHz): 20ms 
- 2581ms, by default it is 20ms.
To verify this I have added mdelay(30) after the RAMP_EN = 0, and there were 
no 'tuck'. However when I increased the RAMP_DELAY (to 40ms, or longer) the 
'tuck' reappeared.

How to solve this?
Realistically we can not add 2581ms delay to the headsetl_event function...
We could keep the VMID enabled all the time (which increases the idle power 
consumption by ~0.001A), but then the muting of the headset 
(HS_POP_GAIN:HSL_GAIN, HSR_GAIN = 0) will give the 'tuck'...
In power consumption the difference between
HS_POP_GAIN:HSL_GAIN, HSR_GAIN == 0 and
HS_POP_GAIN:HSL_GAIN, HSR_GAIN != 0 is about ~0.01A, which is significant in 
my opinion.
Using a timer to finish the ramp down?

Anyways, this seams quite bad. I will think about it over the weekend...

Any ideas?

-- 
Péter