[hatari-devel] EKO System demo

[Laurent Sallafranque <laurent.sallafranque@xxxxxxx>]

Hi all,

I'm back from holidays ;)

Just for info, and to keep a trace of my search.

I've given a quick look at the EKO System demo and here is something 
that may be interresting :

The demo runs until 5 tridi gouraud shaded objects appear on the screen 
and then stops.

When the demo stops, here is the code :

$16524c : 2038 0466                            move.l    $0466.w,d0
$165250 : b0bc 0000 0002                       cmp.l     #2,d0
$165256 : 6600 fff4                            bne       $16524c


Which means that the coder waits for exactly 2 VBLs before continuing 
(if the effects takes only one VBL, he waits another one for better 
rendering I think).
The problem under hatari is that sometimes, the effects is computed in 3 
VBLs, so that's why the demo stops.

If you change the bne instruction by a blt instruction (which means wait 
2 VBLs or more), the demo continues.

w $165256 $6d      (careful to change the opcode at the correct address 
here)

The demo continues to play (with a few glitches, but it continues) until 
the tunnel sequence (I haven't tried yet to see why it stops again).

The fact is that this demo suffers from the Hatari Falcon CPU timings 
(or CPU cycles) (and not at all from DSP<-> 68030 timings) which gives a 
wrong VBL timing.

Another point, Nicolas, you asked for timing tests on various computers.
If needed, I can do some Falcon tests (in VGA mode).

Regards

Laurent