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.