🚀 go-pugleaf

Dave Haynie <daveh@cbmvax.uucp> writes in message <7096@cbmvax.UUCP>

> For a 16 meg system you have 128 table entires, and
> so will occasionally have an ATC miss, though I'm not sure this could
> actually be noticed (The MMU will find the page entry very quickly, since
> except for CARDROM translations it's only a 1-level page table).

The size of the 128 pages that you use is irrelevant, since the MMU will store
in the ATC one entry for each page, where the page size is stored in the PS
field of the TC register. In SetCPU 1.4 you use a rather wierd TC setup, where
the pagesize is 4K. That means that there is an ATC entry for each 4K page,
right?

Wrong! The ATC stores page descriptors also according to function codes, wether
you use them or not. In other words, you get a lot more ATC misses then you
thought, eh?

So if you want to improve a little your ATC hit ratio, simply rearrange your
TC register to use 32K pages. Thus the hit ratio will improve by 1/exp(32/4).
Pretty good tip, eh?

> The 68030 has a smaller ATC,

What I said holds true for the 68851. I just bought the 68030 manual, and will
soon be able to tell what best goes for it.

>Dave Haynie  "The 32 Bit Guy"    Commodore-Amiga  "The Crew That Never Rests"

Valentin
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