[U-Boot-Users] 859/866 clock issues

nyet at mrv.com nyet at mrv.com
Mon Oct 20 20:17:19 CEST 2003

On Mon, Oct 20, 2003 at 01:16:17AM +0200, Wolfgang Denk wrote:
> hello,
> in message <20031018002619.GB325 at zumanetworks.com> you wrote:
> > two minor things on the 859/866
> > 
> > 1) measure_gclk() is very inaccurate. Better to use the plprcr and
> > CFG_8XX_XIN (which MUST BE 10MHz for that cpu) to derive the "real" bus
> > clock.
> What do you mean by "very inaccurate" - the intention of the function
> (as documented) is to measure the "Approx. GCLK frequency in Hz". How
> bad is "very inaccurate" in your case?


the error of using plprcr + XIN is 0%, and given we know XIN is 10MHz
for the 859/866 we are using that now.

> > 2) the 859/866 does NOT support external speeds higher than 66MHz,
> > so if cpu_clk is greater, EBDF01 MUST BE USED IN CFG_SCCR
> I think this is the case for ALL MPC8xx processors  so  far.  I  have
> never seen one which would allow a bus clock > 66 MHz.
> > I have a patch for 1, but i no longer have my 859/866 eval board
> Maybe you can share it anyway.

i'll put something together this week, time permitting.

it will be ugly, but you can see what we tried to do.

> > I have no patch for 2, but eventually we should come up with some sort
> > of solution; the 859/866 is almost always configured to run faster than
> > 66MHz.
> I don't see why a patch should be  needed  here.  This  is  a  simple
> matter of getting your board config file right, isn't it?

yes, but somebody really should add a note to the readme :)

time permitting i will try to.


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