Patrick Mahoney wrote:
>
> Hello pple,
>
> My setup: MPC850 on a RPXlite_dw board.
>
> My problem:
>
> I am trying toggle between power saving modes and evaluate the current
> drops with an ampermeter.
>
> I succeeded in switching to several power modes, but each time i
> switch, my serial connection dies, even if i switch to the  'normal
> low mode', which is supposed to keep all functionnalities  present.
>
> I am looking to use the PIT to automatically bring back the chip to
> normal full power mode.
>
> I tried the following:
>
>       init_timer(&timer);
>       timer.expires=1000;
>       timer.function=timer_handler;
>       add_timer(&timer);
>
> without success. The kernel oops'es everytime. Ive been browsing the
> kernel sources, but have yet to see where the PIT was
> initialized/used.
>
> Would anyone have successfully used the several power modes of the
> mpc850 (or equivalent) through linux 2.4? If so, is there any code
> snippet available?
>

	I have played with some of the power saving modes on our custom
850 board and have had no problems. I have toyed with the Doze High and
Doze Low modes in the idle loop. Attached is a hacked up idle loop for
kernel 2.4.19 that works for me.

Do you have the SCCR[PRQEN] bit set?

Is there any particular reason you want to wake up the processor with
the PIT instead of just letting any old interrupt wake it up?

> Also, do you have any idea as to why the serial connection dies? Is it
> a uart syncing -type problem?

I'm not sure but could the SCCR[CRQEN] bit not being set and a normal low
clock speed set to low to allow the CPM to work properly cause this?

>
> Best regards,
>
> Pat Mahoney
>

You should be able to drop my idle.c in place of the old one. To disable
my hack just comment out the #define MPC8XX_POWERSAVE . My comments
shouldn't be to hard to understand. Also I have the SCCR[PRQEN] and the
SCCR[CRQEN] bits set.

Please let me know how this works.

	Conn
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Conn Clark
Engineering Stooge				clark@esteem.com
Electronic Systems Technology Inc.		www.esteem.com