Re: [hatari-devel] EXA demo Entracte : Improvement in search

[Nicolas Pomarède <npomarede@xxxxxxxxxxxx>]

Le 05/02/2017 à 11:48, Christian Zietz a écrit :
> Laurent Sallafranque schrieb:
>
> > The problem is in the 5 last lines : the code test for a min and max
> > value for register DO.
> > if D0 is not between $4100 and $4200, the code goes to $4eb1c  and this
> > quit the demo immediatly.
>
> To me this simply looks like a CPU speed test, counting the number of
> loop iterations between two VBLs. I'd assume that the demo requires a
> certain CPU speed to run correctly and so it wants to quit on (for
> example) over-clocked CPUs.
>
> I think the 68030 cycle accuracy of Hatari is not good enough here for
> this test to pass.

You're right, this compute cpu speed.

At the moment with my dev version I get D0=$3e65, which is ~5% too slow 
compared to real HW $4100-$4200 for this code loop :

$0001cd1e : 4a78 0468                          tst.w     $0468.w
$0001cd22 : 6600 0006                          bne       $1cd2a
$0001cd26 : 5240                               addq.w    #1,d0
$0001cd28 : 60f4                               bra.s     $1cd1e

Unfortunately, 100 % accuracy will not be reached immediately in Hatari, 
some complex parts of the 68020/68030 pipeline and bus sequencer are not 
known yet to ensure exact similar behaviour regarding how the cpu order 
the memory accesses to be optimum.

Nicolas