Re: [hatari-devel] Very slow emulation when enabling Cycle Exact

[Nicolas Pomarède <npomarede@xxxxxxxxxxxx>]

Le 13/02/2018 à 23:36, Miro Kropáček a écrit :
> On 14 February 2018 at 09:31, Nicolas Pomarède <npomarede@xxxxxxxxxxxx 
> <mailto:npomarede@xxxxxxxxxxxx>> wrote:
>
>     Falcon mode doesn't use TT-RAM, I don't understand what you mean ?
>
> It doesn't by default but one can enable it when testing some software. 
> I've had that feeling that the emulation speed suffers even more but I'm 
> not totally sure about it.

It's normal that falcon emulation is slower when you use TT RAM : in 
that case, instructions accessing memory will take less cycles in the 
emulated falcon.

So when we emulate 1 second, we emulate 16 M cycles. If memory access 
are "slow", you will maybe emulate 1M instructions during 1 second. But 
if memory accesses are twice faster, you will emulate, say, 2M 
instructions (those are just example number to give the idea).

So, during this same second, your host PC will need to emulate twice as 
much instruction, which take make more work.
If your PC/Mac is powerful enough to run this in realtime, you won't see 
a slowdown in emulation (but it will increase your cpu load). But if 
your PC/Mac is too slow (which is the case with 1.6 GHz cpu), then 
emulation will be even slower (it's the same thing if you try to emulate 
a 32 MHz falcon on a PC that can't even emulate a 16 MHz falcon in realtime)

So the rule could be : if your PC/Mac is not powerful enough to emulate 
one machine config, making this same config faster (cpu clock to 32 MHz, 
TT RAM, ...) will make things just worse.

Nicolas