[Letux-kernel] FM Sound

Andreas Kemnade andreas at kemnade.info
Thu Nov 15 13:08:21 CET 2018


On Thu, 15 Nov 2018 09:20:37 +0100
"H. Nikolaus Schaller" <hns at goldelico.com> wrote:

> Hi,
> > Am 15.11.2018 um 07:28 schrieb Andreas Kemnade <andreas at kemnade.info>:
> > 
> > Hi,
> > 
> > some analysis about fm sound:
> > 
> > starting with no sound modules loaded
> > 
> > and then loading this:
> > snd_soc_simple_card
> > snd_soc_omap_mcbsp
> > snd_soc_si47xx
> > 
> > increases idle current by 10mA
> > I have also seen increased suspend current by 10mA
> > 
> > rmmod does not reset these things back to normal. With 4.19.  
> I have checked some more ideas:
Well it worked at least with 3.7

> * pinmux may remain active, but the Si47xx is connected through high value resistors. So there can't be any big leakage current.

Pinmux is already set by uboot. And not changed by modprobe

> * 32kHz - maybe it becomes enabled for the first time but it is used for the WLAN module as well and the DM3730 itself

How should it be enabled then? The si47xx driver almost contains nothing.

> * something inside the si47xx stays in reset state until PCM clocks are applied first and then it is up and running - so it may need a "shutdown" through I2C
>   Looking into AN319 shows that there are explicit POWER_UP and POWER_DOWN commands
>   So we might have to run ./si4721 -dn before removing the driver?
I was not recording/playing anything, so why should any pcm clock be enabled?
I did not run the power up command, just the modprobe.
And it worked some time in the past without any quirks.

I will compare with Letux3704 (no si4721 chip installed)

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