[SunRescue] help with CPU ID

[James Lockwood]

On Fri, 17 Sep 1999, Bjrn Ramqvist wrote:

> So what's the story with the 4/600 and MBus speeds?
> Since we almost always compare the 4/600 with SS10, it covers the same
> problem, 40MHz MBus?
> What will happen if I put in, say dual SM61 or SM51... will they run
> slower than on the SS20 with 50MHz MBus?

The 4/600 does have a 40MHz mbus.  The SS10 has a switchable speed mbus,
some models can do 33MHz and 40MHz (those designed for the SM20), some can
do 36MHz and 40MHz (designed for the SM30).  The 33MHz and 36MHz mbus
speeds were only necessary because TI was having large yield problems with
the 40MHz SuperSPARC CPU's.

An SM61 in a 4/600 will run at a similar performance to an SM61 in a SS10.
The SS20 with an SM61 will be considerably faster.

An SM51 will run at the same speed in all machines, as it is limited to a
40MHz mbus.

Just to add a bit more confusion, CPU modules without e-cache
(SM20/30/40/50) run at exactly the mbus speed.  The practical upshot of
this is that if you take an SM50 (designed for the SS20 as it is the only
system that can run it at 50MHz) and put it in a SS10 or 4/600, it will
run at 40MHz and appear as an MP-capable SM40.  If you're really lucky you
can take an SM40 and run it at 50MHz in a SS20, but the odds of having
this work are slim and you lose MP capability in most cases (only very
late-rev SM40's can do MP correctly).  Since SM50's are so cheap used, a
pair of them make a decent upgrade to a slow SS10.

Some of the more exotic ROSS HyperStations supported even faster mbus
speeds, up to 75MHz.  Only the high-end HyperSPARCs supported these bus
speeds, though.

-James