Cameron Rich wrote:
>
> Hi,
>
> I've been following this series of emails closely as we are interested in
> low power mode also.
>
> I've tried Conn's code, but I'm experiencing problems with PLPRCR[CSCR] as
> being 1 all the time after a rfi. I am also occasionally seeing MSR_POW set
> to 1 after the rfi return.

	An interrupt doesn't change the MSR_POW bit.So seeing the MSR_POW bit
set is to be expected. However there may be a problem with the PLPRCR[CSRC].
The MPC860 and MPC850 User's Manuals were vague on the subject of the
PLPRCR[CSRC] gets cleared by an interrupt if the SCCR[PRQEN] is set. I
contacted our motorola rep to ask about it and he said it was. I have not
checked it to be certain that this was true. On our system everything worked
beautifully so I assumed that this was so.


>
> I can work around this problem by setting PLPRCR[CSCR] = 0 and MSR_POW = 0
> after the rfi and this eventually works. But is this the solution? I'm also

I may be wrong about the PLPRCR[CSRC] bit being reset by an interrupt. It might
be necessary to clear the PLPRCR[CSRC] after a rfi.

I did have something that reset the MSR_POW bit but commented it out because I
didn't think it was needed.

I have attached a revised idle.c that makes certain that the PLPRCR[CSRC] gets
cleared.

> noticing no great decrease in power consumption even though I've only got a
> couple of (sleeping) processes. And it seems that there is (mostly) no time
> between entering Doze Low mode and the rfi which confirms the unsatisfactory
> power consumption figures.
>
> I have SCCR[CPQEN] (and SCCR[PRQEN]) set to 1.
>
> I'm using a PPC850 processor with Doze Low mode set. DFNL=DFNH=0 and I'm
> running 2.4.17 (with a RTAI patch).
>
> Cheers,
>
> Cameron
>

There may be something with the RTAI patch that generates alot of interrupts
or prevents or reduces the time the idle loop from running which would reduce
power savings. Setting the SCCR[DFNL] to a higher number will help.


--

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