On Thu, 16 Sep 1999, Mark Huang wrote:
> Hi,
>
> Is there a way to update the SA-1100's PPCR register and change the core
> clock frequency on the fly after booting Linux? I've tried running the
> assembly code that I use to set the core clock before booting, but that
> just hangs the system usually.
Why would you do that? The problem is that most configurable timings like
dram, IO bus, etc. are all configured relative to the core clock. By
changing the clock you may lose your dram refresh rate and then anything
funny can happen.
One reason to do it would potentially be for power savings. We do it, so
it definitely is possible. The strategy that we use is to basically shut
down all the devices, jump to a very tiny piece of code in flash that
changes the dram configuration parameters, then change the ppcr and then
start up all the devices again. There's some funkiness about the order you
do things in depending on whether you're decreasing or increasing the clock
rate, too.
-Debby
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