Some questions about Winchester/Newcastle cores of Athlon64

[David O'Brien]

On Wed, Apr 06, 2005 at 06:00:01PM +0200, O. Hartmann wrote:
> In some discussions I read about some memory controler issues of
> Winchester based Athlon64 cores.

You have to speak specifics not marketing "core" names.  I can't even
keep them straight -- few within AMD engineering uses them.  What silicon
revision are you interested in?  'C0', 'CG', 'D', or 'E'?  What specific
Athlon64 model?  Athlon64 939-pin's memory controller is different from
754-pin Athlon64 CPU's.

> The CPU will downgrade to DDR333 if 4 double sided memory modules are
                       ^^^
                       DDR400
> present in a system.

This is true for 754-pin (single-channel) rev. C0 & CG CPU's.  I think
this may be true in some cases for 930-pin.  This is simply due to
electrical loading issues.

AMD documents this in publication 26094: BIOS and Kernel Developers
Guild.  See 4.1.3 "Maximum DRAM Speed as a Function of Loading".
http://www.amd.com/us-en/assets/content_type/white_papers_and_tech_docs/26094.PDF

> I also read about a rumor nVidias nForce4 chipset is capable to handle
> 4 double sided memory modules with a Winchester based CPU core,

If you mean a 939-pin CPU, it doesn't have the problem that the 754-pin
CPU's do as it has a dual-channel memory controller.  So each channel is
only driving 2 DIMM's, not 4 on a channel as a 754-pin CPU would.

> but throttling down 1T to 2T access cycles, but remeains in DDR400
> mode.

See what the AMD document has to say about it.

> Is this also an issue of the Newcastle based CPU cores or is this a bug
> in the Winchester cores?

Aggg, marketing names again. :-/

> The oncoming Venice/San Diego cores of Athlon64 CPUs are said to be
> fixed and capable of driving 4 double sided memory modules.
> 
> Is this weird memory controlling behaviour also an issue on Opteron CPUs?

Opteron's will only accept registered(buffered) memory and thus can drive
a higher electrical load on the memory bus.

-- 
-- David  (obrien at FreeBSD.org)