Re: [hatari-devel] Better cycle accurate mode for 68030 / Falcon

[Nicolas Pomarède <npomarede@xxxxxxxxxxxx>]

Le 08/02/2017 à 18:18, laurent.sallafranque@xxxxxxx a écrit :
> Hi Nicolas,
>
> Great job, I'll test this as soon as I'm back home.
>
>
> A few remarks :
>
>
> In hatari 1.8, I didn't use the 32 bits motorola table, but I recomputed every instruction timing for a 16 bits bus + 4 cycles memory access time.
> So, the timings were related to the Falcon bus, not the amiga one ;)
>
> I worked on this with Mikro who exp^lained me how to convert the 32 bits bus to 16 bit bus cycles values.
> You can find a doc about this on his site : https://mikro.naprvyraz.sk/  in the "docs" section (68030, ST RAM and things around it).

Hi

ok, that explains why your table were not that bad :)  (note that 
motorola timings are not necessarily the amiga ones either, because the 
amiga also has several bus size / ram speed depending on the kind of 
memory expansion)

> Another point : Rodolphe did many measurement about the cycles used by the Videl : you can find this on his site :
>
> http://rodolphe.czuba.free.fr/CT2/english/technic.htm
>
> The general idea is that the Videl reads the st memory in longs burst mode,
> This can take from 4 up to 32% of the band width of the bus.

Yes, I know this page, including the 2 scan of notes he took on paper :) 
 That gives some idea and it's better than nothing, but that's not 
precise enough. When does the burst start ? When DE signal is on or 
before ? Does it preload during border ? How long does the burst last ? 
And so on. We lack a description of the signals at the bus level to see 
how and when videl get access.

For now, I could "slow down" the CPU bus access by 20% in true color 
mode for example, this would give an overall correct average, but that's 
not the cleanest way.


I think that now you could commit your improved videl code. Accuracy is 
not 100%, but it should be good enough for most cases (and since pinball 
dreams doesn't work now, it could only improve things anyway)


Nicolas