[hatari-devel] Lower emulation ressources in 68000 cycle exact mode

[Nicolas Pomarède <npomarede@xxxxxxxxxxxx>]

Hi

I just pushed some changes to do_cycles_ce() to require a little less 
cpu ressource. This function is called after every cpu instruction is 
emulated, so even small optimisations can have positive effects.

In the case of the Amiga and WinUAE, emulation needs to update other 
components (blitter, video, audio, ...) every 2 cycles during the 
emulation of each cpu instruction.

In the case of Hatari when emulating STF/STE machines, this is not 
required. So we can replace this loop :

while ( <n times> )
 do_cycles ( 1 * CYCLE_UNIT );

with :
  do_cycles ( n * CYCLE_UNIT);

From a quick benchmark when running some demos, I go from ~134 emulated 
VBL/s to 143.3 VBL/s, which gives 7% increase in emulation speed.

It's only when running in STE mode and blitter is enabled that we use 
the slower "sub cycle" version to emulate that part of the last cpu 
instruction can run in parallel with the blitter.


Nicolas