Re: [hatari-devel] Data cache Issues?

[Nicolas Pomarède <npomarede@xxxxxxxxxxxx>]

Le 06/06/2015 20:14, Eero Tamminen a écrit :
> Hi,

> > So standard 68000 packers like the STF are not correct if they don't
> > flush the caches at the end, there's nothing Hatari can do about this.
>
> Why someone would pack Falcon program with a packer that doesn't
> work on Falcon?
>
> Or is it normal for people to (somehow) disable caches before they
> run (these) demos, or Beats of Rage game?

hi

I don't know, maybe because they never noticed it could create some crash ?

For example beat of rage doesn't work for you with cache but it always 
works for me. So depending on the programm (*.acc or others) launched at 
start before you start a packed program, the instruction cache can be in 
a "random" state. It's only 256 bytes, so most likely the old / not 
flushed entries will be replaced before PC points to them.

But in the case it happens, boooom ! you get a crash, for example 4 
bombs "illegal instruction" like I saw from time to time when running 
virtual city (from pouet.net) before I added flushing for the 
instruction cache in gemdos HD Fread too.

If the depacker doesn't flush the instr cache, you can be sure a crash 
can happen ; depending on the packers, some of them are moving the 
depacked code at the same place that the depacker code was (to reduce 
memory footprint), so chances of getting a cache mismatch are even higher.

Nicolas