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Demos Amiga Demoscene Archive Forum / Coding / 68020 Instruction Cache on Vanilla A1200 (?)


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#1 - Posted: 12 Nov 2016 14:42
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Hello y'all.
It's been yeaars since I last posted here.

One very simple yes/no question.
Knowing that a non-accelerated A1200 has only Chip Ram.
Knowing that a non-accelerated A1200 has a 68020 with a 256b instruction cache

Knowing that other configurations that have data cache, can't load/use chipram in data cache...

Can the 68020 of a non-accelerated A1200's instruction cache, cache the Code in Chip-Ram ?
Or does it makes the 68020 Inst. cache completely useless on such machines ?
#2 - Posted: 13 Nov 2016 13:23
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I have a vague feeling that I've used the disable cache option in the early startup menu of an unexpanded A1200 to run older software with self-modifying code. Can't swear that it was unexpanded though. I've also read in tutorials that you should keep your loops smaller than 256 bytes on A1200. I'd be shocked to learn that the cache isn't available on unexpanded systems!
#3 - Posted: 13 Nov 2016 17:37
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i "think", that as the 020 only have instructions cache, and the cache that is normally disabled for chipmem access is Data Cache. That the 020 does allow for ICache of chipmem stored instructions.

ACAtune Wiki
"On most Amiga accelerator boards, accesses to Chip-Ram either disable the CPU caches completely, or only allow instructions, but not data to be cached."

But i'm not 100% sure im "Thinking" correct.


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