[maemo-developers] ALSA sound driver for Nokia 770 and DSP programming

[From: Felipe Contreras]

On Thu, Sep 25, 2008 at 10:07 PM, Siarhei Siamashka
<siarhei.siamashka at gmail.com> wrote:
> Hi,
>
> As has been discovered long ago [1] but eventually forgotten, Nokia 770 has
> AIC23 audio hardware [2] which can be used not only from DSP side, but
> from ARM as well. Moreover, OS2006 kernel sources even contain an ARM driver
> for it, but this driver is disabled (that's understandable as the driver is
> not in a very good shape and has quite a number of bugs).
>
> Recently I have been trying to make it running and seems like we have a very
> good chance to have it working nicely. It is also interesting, that the
> linux-omap guys seem to be developing a new driver [3] for AIC23 which may
> eventually become a better alternative.
>
> Kernel patch is attached. It enables AIC32 driver, adds a hack to
> power on/off code so that audio codec is permanently powered on (power
> on/off code is not reliable and needs to be reworked). Also it fixes a
> problem with audio stuttering on video playback in mplayer (the driver
> had broken position reporting which is critical for proper audio/video
> synchronization).
>
> Here is some usage instruction (beware that standard disclaimer applies:
> you can use this patch at your own risk, this code is quite untested. If it
> somehow manages to fry your device, you have been warned and I'm not
> responsible for any breakages):
>
> 1. Disable esd daemon and DSP stuff in order to move it out of the way
> (temporarily rename '/usr/bin/esd' and '/usr/sbin/dsp_dld' to something else)
> 2. Apply the attached patch to OS2006 kernel, compile and flash it to the
> device
> 3. Compile and install alsa userspace library, I used alsa-lib-1.0.11.tar.bz2
> 4. Put attached 'asound.conf' into '/etc' directory on the device, it enables
> dmix plugin for audio mixing and resampling
> 5. Compile and try some applications which use ALSA, I tested 'aplay'
> and 'mplayer'
>
> The driver is semi-usable now, but a lot still needs to be done:
> * proper power management to avoid excessive battery drain
> * audio volume control
> * switch between speaker/headphone
> * audio quality is a bit crappy now, this needs to be fixed
> * maybe some more fixes for bugs that are yet to be discovered...
>
> DMA code is quite suspicious (especially the way it does channels linking) and
> might be responsible for audio quality issues. Also sofware mixing/resampling
> code in dmix plugin can benefit from ARM optimizations.
>
>
> Now regarding why we may want it. Once if we get a good, low latency, fully
> functional and reliable ALSA sound driver running on ARM, it gives maemo
> community a nice possibility to scrap all the proprietary DSP binaries. This
> provides us with a new and shiny 252MHz C55x DSP core ready to be used by
> something else :)
>
> Free linux DSP toolchain from TI [4] supports generation of both DSP kernel
> and DSP tasks for OMAP1 based devices which is sufficient for DSP development.
> The toolchain license was supposed to permit open source development (with
> noncommercial restriction), though the license text itself is a bit
> questionable [5].
>
> With DSP avalable for use and having no need to spend efforts on ensuring
> compatibility and peaceful coexistence with proprietary binary codecs (free
> and proprietary code does not mix well), it should be possible to turn
> Nokia 770 into quite a powerful media player.

Great stuff!

Do you plan to use the dsp-gateway or dsp-bridge?

-- 
Felipe Contreras