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Re: [ECOS] MBX hal clock settings
- To: "Hugo 'NOx' Tyson" <hmt@cygnus.co.ukx>
- Subject: Re: [ECOS] MBX hal clock settings
- From: Jamie Guinan <guinan@bluebutton.com>
- Date: Tue, 27 Jul 1999 09:50:03 -0400 (EDT)
- cc: ecos-discuss@sourceware.cygnus.com
- Reply-To: 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