Re: [hatari-devel] Suspected Hatari 2.3.0 regression (prefetch?)

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Le 16/12/2020 à 01:13, Eero Tamminen a écrit :

According to real device test results done with byte and word access:
https://git.tuxfamily.org/hatari/hatari.git/tree/tests/buserror/results

Only palette regs are readable, not the the area
after them.

If prefetcher triggers now (2.2 -> 2.3) access
errors when reading something that program didn't
actually read, that does sound like a regression
bug.

Hi

well toni improved cpu prefetch/bus error a lot and this new version is now in hatari 2.3, so this might explain differences (although I have the feeling cpu core is now more correct than before, so maybe it's hatari 2.2 that did not have the correct behaviou ?)à


Nicolas, any idea why MMU would prevent those?


(I've been wondering about why some programs now
need MMU, and bug like this sounds a plausible
explanation.  Toni is less likely to run across
issues of bus errors happening at wrong place
with Amiga, or it could be Hatari integration
issue.)

MMU emulation for 68030 is complex, it's possible that at this point not all HW accesses that trigger a bus error in non MMU mode are correctly emulated in MMU mode and the bus error is not correctly triggered, which would allow buggy programs to work only in MMU mode instead of crashing.

Now that we have several examples in compat list, I will check them later in more detail to really see what is happening at the cpu core level. But in all cases it would be good to have confirmation on a real falcon if these programs are working or not.

Note that as real falcon have a MMU enabled, it's possible that those programs are buggy and only work emulated when using the MMU because it catches bus error.
Anyway, can't be sure at the moment, need to look at precise examples.

Nicolas



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