| Re: [hatari-devel] rev 3689 : splitting cpu cycles above 20 |
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On Sat, 7 Jan 2012, Nicolas Pomarède wrote:
> (I don't even know if some falcon demos are doing "sync" code with
the video beam ?)
I think I've seen most, if not all, Falcon demos and so far no hardsync
demos. I don't think it's possible to do in a reliable way with all DMA
stuff affecting CPU bus access.
I don't think timings are not important, I just say it's *really really*
complex to measure on the falcon, and that the falcon mode is not ready
enough for this.
I don't think it's necessary to have the 030/Videl in exact sync, HBL
would be a good thing to have though (a few demos uses HBL/Timer-B for
splitscreen/rasters).
The timings that are of most importance are CPU:DSP, many demos rely on
the ratio to be 1:2 and have the correct speed (also need memory bandwidth
simulation to be solid). Eg, a normal CPU-loop can be:
move.w (a0),(a1)+
Where a0 is the host port and a1 ST-RAM. The speed on the ST-RAM access
greatly differs between resolutions used. If the emulator doesn't take
ST-RAM bandwidth into account, demos will crash because of the too fast
CPU loop. This is also the reason why a lot of DSP demos fail on
accelerator boards, the 1:2 ratio is off. Of course, cleanly coded DSP
programs won't crash, but they will also have slower transfer (sync code
in the CPU-loop).
There're many roads to reach a good falcon emulation, my opinion is that
focusing too much on cycle exact problems for now is not the most efficient
way, I'm sure there're many other parts to improve that don't require 100%
accuracy and that would improve user experience a lot in demos for example
(sound problem as reported by anders in dspmod, videl)
If Hatari evolves (and I really really hope it will) to support
faster CPU and FastRAM, the huge work on clockcycle exact 030-Videl won't
be of any use (perhaps even make things worse?).
--
Anders Eriksson
ae@xxxxxx http://www.dhs.nu/
ae@xxxxxxxxx http://www.atari.org/