[maemo-developers] Frequencies scaling with OS2008

[From: Frantisek Dufka]

Igor Stoppa wrote:
> Having the audio path open, but no dsp tack loaded (arm audio) sets the
> clock to 400MHz.

Interesting, so, umm, there is way to play audio from ARM side directly? 
What I tried is to play BBC radio in home screen applet which activated 
only pcm2 task and arm clock dropped from 400 to 330. That lead me to 
conclusion that there is no way to output audio with arm clock at 
400Mhz. Why there are pcm tasks (used when streaming internet radio) if 
we could output audio from arm side without limiting ARM clock? Siarhei 
apparently used a way to output audio without activating DSP from 
mplayer, how?

Indeed there is something in
arch/arm/mach-omap2/board-n800-audio.c
arch/arm/mach-omap2/board-n800-dsp.c
that looks like there is a way to (partly?) power up dsp, do not run any 
task and send audio from arm side?

As for the policy I had a look at arch/arm/mach-omap2/board-n800-dvfs.c 
and there are four states defined OP_0 to OP_3 and two additional ones
OP_DSP_H (H=high?) and OP_CPU_H as aliases to OP_1 (330/220) and OP_0 
(400/133). So one could probably redefine OP_DSP_H to different OP_X to 
try running dsp at different clock and see which dsp tasks are not fast 
enough.

Also I wonder what happens when I set DSP_CLK_KHZ in OP_0 state to 
266000, can I damage the hardware or will the DSP just crash (leaving 
rest of the system relatively OK)?

Some comments would be nice there like e.g. which clocks in the table 
are tied together or which combinations (dsp vs mpu vs other) are allowed.

BTW, are you forbidden to put any meaningful comments about the hardware 
there? If yes then how come you are allowed to publish the code itself?

Frantisek