[hatari-devel] Suspected problem iwith TimerD patch

["Roger Burrows" <anodyne@xxxxxxxxxxxx>]

Hi all,
On the EmuTOS list, Eero reported that the program Bomb Squad 
(http://www.atarimania.com/game-atari-st-bomb-squad-falcon030_21766.html) runs 
a lot more slowly under EmuTOS (latest version) than under TOS4.04 (both 
running under Hatari 2.2.1).  After lengthy investigation, I believe that this 
is caused by a Hatari problem.

Using the following synbols:
  H    Hatari
  TR   TOS 4.04
  ER   EmuTOS in ROM
  EP   EmuTOS as a PRG
  BS   Bomb Squad
  ->   "runs"
here's a summary of what I found:
  H->TR->BS        ok
  H->TR->EP->BS    ok
  H->ER->BS        slow
  H->ER->EP->BS    slow

I first thought that EmuTOS was failing to initialise something that TOS4 
initialises, but I was unable to find anything.  However, I turned on MFP 
tracing ("trace mfp_start") and noticed a difference in the entries for CD 
handler 7 (the one used for Timer D).  For TOS 4.04, the entry says:
 ..... data=100 ctrl=7 timer_cyc=20000 .....
whereas for EmuTOS it says:
 ..... data=100 ctrl=1 timer_cyc=400 .....

After reading the comments in Hatari's mfp.c, I interpret this to mean that 
when running EmuTOS, Hatari will have to evaluate the interrupt queue much more 
often than it would on TOS 4.04, causing a major slowdown on my somewhat slow 
system.  I made a simple change to Hatari (in mfp.c, commented out the line:
	bAppliedTimerDPatch = true;
in function MFP_TimerCDCtrl_WriteByte()), and re-ran the above tests and 
tracing.  The "trace mfp_start" output under EmuTOS looked the same as under 
TOS4.04, and there was no slowdown.

Of course, my change almost certainly is much too simplistic, but I believe 
that the above test shows that this is a Hatari problem that ought to be fixed.

Roger