Adding Symmetric Multiprocessing to Amiga UNI

[Dave Haynie]

In article <1991Jan31.154251.16107 at nada.kth.se> nv90-mho at dront.nada.kth.se (Magnus Holmberg) writes:

>	I'm not very good at hardware (esp. w/ the 3000). It seems
>	to me, though, that since the '040 wouldn't need to access 
>	Chipmem much, in a setup like this, it might be possible to
>	run it on the same 'half-cycle' as the PAD. That way, the
>	CPU's wouldn't have to lock eachother out of the Fastmem-bus.

The 32 bit bus is fully loaded by any '030 or '040 access; there's no spare
time like there was on the 7.16MHz 68000 systems.  Think of it this way --
the 68030's clock is 3.49 times that of the Amiga 68000 machines, and a
68030's fastest cycle is twice the speed, in clock cycles, of the 68000's
fastest cycle.  So, in order to run double cycles without wait states on an
A3000, you would need a DRAM chip that cycles in roughly 20ns (that's a
simplification, but you get the main idea).  The 80ns parts in the A3000
are cycled at 200ns, 10 times too slow for such a trick.

The best strategy for A3000 multiprocessing would be to have the 68040 off
the main (shared) bus as often as possible, while the 68030 does whatever
I/O operations it can handle.  The large 68040 cache makes this a somewhat
natural event anyway, but either private 68040 memory or a large external
cache on an '040 coprocessor board would improve this considerably.

>		    -MH		


-- 
Dave Haynie Commodore-Amiga (Amiga 3000) "The Crew That Never Rests"
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	"What works for me might work for you"	-Jimmy Buffett