How to change Bus speed for MPC8xx CPU
wd at denx.de
Sun May 18 20:27:08 EST 2003
In message <E19HJpf-000JCU-00.xol-mail-ru at f25.mail.ru> you wrote:
> 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
> 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
Try changing the multiplicator factor to 8, so you get 80 MHz CPU /
40 MHz bus clocks.
> 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.
> 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.
Software Engineering: Embedded and Realtime Systems, Embedded Linux
Phone: (+49)-8142-4596-87 Fax: (+49)-8142-4596-88 Email: wd at denx.de
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