Re: [hatari-devel] test needed on a 4MB STF

[Nicolas Pomarède <npomarede@xxxxxxxxxxxx>]

Le 22/12/2016 à 18:49, Christian Zietz a écrit :
> Nicolas Pomarède schrieb:
>
> > We know that if we access an address > mmu_size0 + mmu_size1 then we get
> > an "empty" region up to 4MB where the STF will return the last word seen
> > on the bus
>
> When you say "empty region", you probably mean that no RAM access
> signals (/RASx, /CASxL, /CASxH) are being generated, right? I have to
> look up how the rules for generating these are.

From an HW point of view, I don't know if the MMU doesn't generate any 
RAM signal, I guess it's the case.

If RASx/CASxL/CASxH are not generated with the correct timing of the 
"read cycle" chronogram for example (as detailed in the OKI 41256 
datasheet), does it mean the ram modules doesn't change its previous 
output state, which would mean the 16 RAM modules would keep their 
latest Dout value ? (usually this is the last word prefetched by the 68000)

If so, I understand why RAS/CAS would not be generated when accessing 
addresses beyond mmu_size0 + mmu_size1, but I don't see why it would 
also be the case with this 128/2048.

Might be some bit combinations again that are supposed to work when we 
go beyond total ram, but that triggers in some unexpected cases too.


> > Do you see this "hole" too on your STFs between 40000 and 80000 ?
>
> I'll see if I can do the test later.
>
> Regards
> Christian