Re: [ECOS] MBX hal clock settings

[Jamie Guinan <guinan@bluebutton.com>]

On 27 Jul 1999, Hugo 'NOx' Tyson wrote:

> Jamie Guinan <guinan@bluebutton.com> writes:
> 
> > I was studying the MPC823 clocks, and I noticed what
> > appears to be a small error.
> > 
> > In packages/hal/powerpc/mbx/v1_2_3/src/mbx.S, the setting
> > for the PLPRCR register at 50MHz uses 0x5fa in the MF
> > (multiplication factor) field.  Doing the math, I get,
> > 
> >   50*1000*1000 / 0x5fa = 32,786
> 
> Interesting, I get 32680 as the nearest value here.  But never mind...

You're right.  I don't know where my head was that I came up with
that number.

> > The crystal is suppoed to be 32,768 (not 86), so I belive
> > the appropriate value should be 0x5f5.
> > 
> >   50*1000*1000 / 0x5f5 = 32,768
> >
> > There is actually some remainder there, but with 0x5f5
> > the frequency is low by 28.8Khz versus over by 135KHz
> > with 0x5fa (assuming the crystal is accurate).
> 
> Yup; I agree, I've patched our sources, this will take effect as and
> when... (next week for anoncvs users)
> 
> Of course, this gives us a performance hit... we were successfully
> overclocking!  ;-)

:)

Actually, 0x5f6 will bring you even closer to (ideal) 50MHz, and only
overclocks by 3KHz (hopefully my brain is working better today).

> Small issues/typos like this, posting here works fine.

Ok.  

Thanks,
-Jamie