[SunRescue] CPU modules for the SS20

[James Lockwood]

On Sat, 25 Mar 2000, Maarten Deen wrote:

> is there a list or an overview of available CPU modules for the 
> SS20? For one, I can hardly find a reference to the one I've got: 501-
> 2925, like the size of the cache.

http://www.uutil.ic24.net/mbus/mod/ is a handy reference.

501-2925 is an SM71.  75MHz SuperSparc-II, 1MB e-cache.  You can type
"module-info" at the ok prompt to get most of this information.

> I'd also like to know what happens if you mix CPU modules of 
> different speed. The only 'bad' thing that can happen is the MBus 
> speed going down to 40 MHz when the slowest requires it, right?
> For this reason I'd like to know which modules run on the 40MHz 
> bus and which on the 50MHz.

All MBus modules (except possibly the fastest HyperSparcs) can run at
40MHz.  The SM50/SM61/SM71/SM81 and all HyperSparcs except for the early
55MHz modules can use a 50MHz MBus.  Some faster HyperSparcs (I only know
about the 133MHz, 142MHz, 166MHz and 200MHz for sure) can use the 66MHz
MBus supported in the Ross HS30. 

Mixing modules in general is bad.  Some workarounds for module-specific
bugs are performed in the PROM at bootup.  The only ones that are
probably "safe" to mix are:

MP-capable SM40's (rare!) and SM50's (40MHz MBus)

SM51's, dual SM51's and SM61's (40MHz MBus)

SM71's and SM81's (non sun4d, disable multiple commands)

Probably most HyperSparcs.

I wouldn't advise it, though, the scheduler assumes that all CPU's have
the same speed and you may get serious resource starvation with mixed
modules.

-James