MiSTer FPGA Forum

I'm confused by the behaviour of data cache setting on the 68020 processor options in minimig.

With this option enabled, no data cache is detected by the amiga - for instance using sysinfo to show instruction/data cache state, or command-line tools to show/enable/disable caches. The instruction cache is detected.

Granted, the cache may well be implemented in a way that's not visible to the simulated amiga hardware, which would be in keeping with the 'pretend' 68020 as that chip did not have a data cache.

What's really confusing though is how the amiga behaves with the cache switched on/off.
Using sysinfo as a benchmark, there's no difference in performance between having d-cache switched on or off - the results are identical.

Is the cache setting working? Is it always enabled or disabled regardless of the gui setting?
Am I just "holding it wrong"?

As I say, confused.

Hi Toastboy,

One year ago, Sorgelig gave some information regarding this D-Cache (see here : https://www.atari-forum.com/viewtopic.p ... 75#p385606)

On my side I saw the benefit by using the D-Cache on some demos where they were boosted compared to w/o.

Sysinfo is not a best benchmark. Its reliability is very low. You can see millions points in SysInfo in emulators while most of them will suck when you run A500 demo such as "State of the Art".
Still it's good to compare the points between version of the same implementation.

Implemented 68020 CPU never had D-Cache, so apps obviously cannot detect it as they rely on CPU features, not actual test. So D-Cache is fully transparent for apps. Effect of using D-Cache depends on specific app/game.

Thanks for the explanation sorgelig. Surprised you have time to reply to anything with all the recent aspect-ratio changes

Some games, for example, work better with D-Cache off. WHDLoad version of Uridium II shows sound glitches with that option on, so you need to turn it off.

Wrong thread sorry!