Re[2]: How to change Bus speed for MPC8xx CPU

As far as I understand there is a bootloader provided by board
manufacturer this is something like BIOS in desktop pc.
And there should be part of the kernel running before
the kernel starts. So which one of them do the job with
clocks? Or probably both of them.
And there the kernel loader sources are located under
/usr/src/linux tree. I would like to put my patch inside and paly
with it.
Thanks.

-----Original Message-----
From: Wolfgang Denk <redacted>
To: "XOL" <redacted>
Date: Sun, 18 May 2003 12:27:08 +0200
Subject: Re: How to change Bus speed for MPC8xx CPU

In message [ref] you wrote:

quoted

 cpu MHz : 100
 bus MHz : 50

 My board is runnig from external clock of 10M and boot monitor
 has parameter called mulitplier which is equal to 10.

10 * 10 MHz = 100 MHz CPU Clock.

100 MHz CPU clock / 2 (see EBDF bits in SCCR) = 50 MHz bus clock

quoted

 I need to slow bus speed to 40MHz and from 862 data sheet I see
 what this can be done by writing to internal registers of clock
 engine.

Try changing the multiplicator factor to 8, so you get 80 MHz  CPU  /
40 MHz bus clocks.

quoted

 My question is how kernel deal with it. Where and how clock are configured
 and how can I change it. Is it done on the boot time by kernel boot loader ?

The kkernel does not deal with this at all. It  receives  information
about the system clocks from the boot loader.

quoted

 Maybe you can apoint me to the source in kernel where clock parameters
 are configured. IMHO it should be somwhere in boot.

This is done in the boot loader.


Best regards,

Wolfgang Denk

--
Software Engineering:  Embedded and Realtime Systems,  Embedded Linux
Phone: (+49)-8142-4596-87  Fax: (+49)-8142-4596-88  Email: wd@denx.de
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watches is never sure.                                       Proverb

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