Anyone using FR as a phone? / Audio Codec meddling info

Al Johnson openmoko at
Mon Jul 21 23:47:17 CEST 2008

On Monday 21 July 2008, Andy Green wrote:
> Somebody in the thread at some point said:
snip my comment about alsa settings bypassing the ALC

> I don't know why we go around it, but when I looked mic -> GSM routing
> some weeks ago I also found a very direct analogue path.  If you're
> interested to meddle with this, I have some meddling hints.  First, the
> datasheet is open:

I've been reading it already ;-) One area the wiki does well on is links to 
the hardware datasheets.

> We have fitted 100n in the external ALC path (between ACOP / ACIN)
> instead of 1uF recommended, I guess it will impact low end, but in
> telephony the low end as well as the high end are chopped out anyway.
> Soon, as steve told, you'll be able to see this stuff (and our mistakes)
> on the schematics for yourself.

I didn't notice a rolled off low end in cursory testing of the ALC, so you're 
probably right. It's good to know just in case though. Steve's announcement 
was a pleasant surprise, and I'm looking forward to it.

> You can dump the actual codec registers using
> # cat /sys/devices/platform/soc-audio/codec_reg
> and you can meddle with them like this
> # echo "3d 20" > /sys/devices/platform/soc-audio/codec_reg_write
> first one is the register address in hex, second is value to write in
> hex.  I don't really know what those dozens of alsamixer settings are
> doing either, I found it easier to read the datasheet and interpret /
> meddle with the codec registers directly.

That'll be handy. I'll check my mapping of the ALSA devices and settings 
against this. I don't want to stick it on the wiki before I know it's right.

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