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Re: Booting the Debian installation CD on Powerbook G4 12"

On Wed, Feb 19, 2003 at 03:26:42AM +0100, Segher Boessenkool wrote:
> Benjamin Herrenschmidt wrote:
> >On Mon, 2003-02-17 at 02:07, paubert wrote:
> >
> >>Well, the timebase and decremeter are part of the PPC architecture. 
> >
> >I'm not sure things like 4xx implement them "as-is"...
> It is part of the user-level 32-bit PEM -- they better
> implement it :)
> >>BTW for the "53 MHz PB", what are the following properties of 
> >>cpus/PowerPC,G4: 
> It is 53_300_000 Hz, and it is most probably a typo
> in the OF.  All other such values are rounded to
> exact millions.
> If you're going to reimplement the delays using the
> time base, why not use the KeyLargo timer instead?

And tie the bus on repeated I/O trying to read the timer, fighting
perhaps with another processor on SMP?
No thanks.

> It runs at the same frequency (18.432MHz) on all
> machines, so that'll save a multiply ;)  Too bad for
> the non-Macs, but else you'll have to special-case
> the 601 (and maybe others) anyway.

I don't know how you'll avoid a multiply unless you want
to pass delays in strange units. It's better to have the
multiply in one place in the called function rather
than have one in every caller of non constant delay.

After all, we could even patch the code at boot time
so that the multiplicator is not loaded from memory
but just inline. Something similar is done for hash
table addresses already.


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