[U-Boot] [PATCH v2] at91: change CONFIG_SYS_HZ to 1000

[Sergey Lapin]

> > But the config file for afeb9260 sets it to a value of 89999598,
> > and I can't change that as I don't know that board, but it's
> > near enough to 100000000 to accept that.
> > And I noticed that only because I had the check there in the
> > first place, so it didn't compile with MAKEALL when I only checked
> > for the exact value of 100000000.
> 
> That's a very obscure reasoning, me thinks. We don't  understand  the
> 89999598,  so  we  accept  85000000...115000000  ?  That's true vodoo
> programming.

I can explain this stuff about master clock :)

1. AT91SAM9260 CPU is run from PLLA on this board. PLLA runs at
180MHz there as maximum stable speed (Actually there are
boards with smaller value, I have revisions for 166 and 133MHz
here and I want to provide a few patches about this stuff).
But 180 MHz is not exact value and it is from 18429952 by multiplication
and division. And we need to use it as close as possible because
ALL peripherals, except USB depend on this value for timings.
Also, a problem is that not all combinations and divisions actually
work, and that is hardware feature, too.
That's because it is not possible to get this 100MHz value,
it is just it - you can't get 100MHz by division of 180MHz
by any integer value starting from 2.

I don't see any real reason to pretend we have always 100MHz on
this CPU. That might harm a lot. And you can't even imagine how nasty
this hardware can be.