timeout while detecting SD card

[Bernd Walter]

On Wed, Jun 06, 2007 at 10:09:39AM +0200, Björn König wrote:
> Krassimir Slavchev skrev:
> 
> > I use MCK 80MHz and cpu clock 240MHz without any  problems.

My first overclocking was 288MHz, which was surpisingly stable.
It happend because I oversaw a crystal definition and compiled the
PLL init code for 10MHz, while my boards have 16MHz.
But be carefull - MCK of 60MHz is still hardcoded in a few places.

> I would assume that certain devices won't work properly. I doesn't have
> much experience with the at91rm9200, but with at91sam7s256. The
> controller's maximum MCK(=PCK) is 55 MHz according to the specification,
> but actually it worked almost fine with 96 MHz. At least USB didn't work
> properly anymore, but most peripherals. Obviously there are many reserves
> beyond the specification and I think it behaves potentially similar with
> the at91rm9200.

That's not neccessarily the case with the RM9200.
It is only the PLL, which is limited to 180MHz.
MCK of 80MHz is OK and PCK of 209MHz is OK.
It is just that you can't get a PCK of 209MHz without overclocking the
PLL.
MCK is divided from PCK, so you can get 80MHz only with reduced MCK
or higher PCK.
Since almost every board has PC133 SDRAM chips even SDRAM access a
MCK of 80MHz is fine here as well.
With the 240MHz you overclock the PLL and CPU, but MCK and external
components are within their range - on the other hand it speeds up
everything, from CPU to RAM.

In fact the PLL was designed 240MHz on not for 180MHz as defined now.
I asume Atmel just reduced it because of problems under edge conditions
such as full temperature range.

-- 
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