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Re: Frequency (cpu speed) control on AU1100

To: Bob Lees <bob@diamond.demon.co.uk>
Subject: Re: Frequency (cpu speed) control on AU1100
From: Pete Popov <ppopov@mvista.com>
Date: Tue, 30 Mar 2004 14:48:34 -0800
Cc: Dan Malek <dan@embeddededge.com>, linux-mips@linux-mips.org
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Bob Lees wrote:

On Tuesday 30 March 2004 22:56, Dan Malek wrote:
Bob Lees wrote:
> ....I suspect I am
missing something somewhere, but I can't find any references to cpu speed
control for the MIPS processors, specically the au1x range.
The Au1xxx has a PLL that multiplies the incoming 12 MHz clock up to the
internal frequency.  Just be aware there are lots of peripheral clocks
and bus clocks derived from this internal frequency.  There is code
in the kernel power management to allow changing the frequency during
operation of Linux, but I don't know how well it works today as I have
not tested that for quite some time.

Thanks.
        -- Dan

Thanks Dan & Pete for the prompt response. I have tried the /proc/sys/pm/freq interface and by putting a bogomips calc into power.c, it appears to indicate a change in core frequency. I think your caution may be well founded as I got input overruns on the serial console when I took the speed down to 84MHz, good character recognition though, so it was an input buffer speed issue.

Also I can see an approx 40-50mA change in current from 84 to 396MHz which indicates something is changing. Supply is at 5 volts thru a simple switcher down to 3.3 volts on the Aurora board. This is with nothing else running and an nfs filesystem. As part of monitoring current I am seeing an anomoly: namely after boot is complete and system is quiesent, at apparently 396MHz, the current is 200mA, now after playing with the freq control the current at 396MHz stabalises at around 250mA. Verrry strange - any thoughts??
Is the 250mA after you've done a new power cycle, which doesn't make sense, or after you scale down to 84 and back up to 396MHz?

On another topic, what state is the IRDA driver in?
It works. Check out the IrDA readme on linux-mips.org:/pub/linux/mips/people/ppopov/2.4. I've tested two boards back to back using the network layer at FIR speeds, and a board to palm pilot using SIR. It's all in the readme.

This is building from the patched 2.4.25 kernel on your site Dan. And a big thank you for this source of a patched kernel and build tools.

Pete

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