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Re: call for help: CPU clock speed on PowerBook5,6

Hi Jochen,

Jochen Voss <voss@seehuhn.de> writes:
> My questions:
> 1) It seems that writing 5 into the register mean full voltage and and
>   writing 4 means derated voltage.  Is there some documentation about
>   the GPIO?  How long does one have to wait after setting the voltage?
>   Should I be able to read back the current value using

There is not really any proper documentation about this stuff, but the source
code for Darwin is available on the Apple developer web site, so you can see
exactly what they do. The package that deals with this stuff used to be called
AppleMacRISC2PE. A simpler way is to find the code in your open firmware which
knows how to change the frequency. On the iBook G4 I have, this is at
/cpus/PowerPC,G4@0, I have set-dfs-high, set-dfs-low.

> 3) Can anybody think of another way to debug this problem?  Are there
>   other potential causes for the crash?

Sorry, I have not been keeping up to speed with kernel development lately, but
I might be able to offer some suggestions; I wrote the original 7447A cpufreq
patch, with Ben's help. While writing the code, I found that a crash was bound
to occur (but not immediately) if the cpu was put into high speed mode without
changing the GPIO to high voltage.

If you look back at the linux-ppc-dev archives from May 2004, there are some
posts there about it. There may be some clues there.

So far we have been assuming that the new PowerBooks behave the same as the
older ones with the 7447A chip. If this is true, then I would suggest starting
with a known good kernel (e.g. I know 2.6.10 works with cpufreq on my ibook),
and then just adding your PowerBook string to the pmac_cpufreq_setup()
function in pmac_cpufreq.c, with the other 7447A CPUs. Also duplicate the
Powerbook5,4 entry in pmac_mb_defs (pmac_feature.c), but change the string as
appropriate for you machine.

I think what you have suggested (cpu doesn't like going high speed without
elevated voltage) makes the most sense. In one of your previous posts, you
mentioned something in pmac_feature.c where there is some code relevant to
Powerbook5,4, enabling that for your machine is worth a shot too. I don't
have 2.6.11 sources here yet . . .



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