Re: [stella] Supercharger Bankswitches and RAM access!

Subject: Re: [stella] Supercharger Bankswitches and RAM access!
From: Chrissalo@xxxxxxx
Date: Sat, 15 Mar 1997 08:54:41 -0500 (EST)
Might as  well answer to the list as well :-)

Hi!

<< >How is the value determined using indirect-x and indirect-y?
 >How is the address determined using indirect-x and indirect-y?
 
 The value is accessed address minus $F000
 The address to write to is the address that is accessed 3 or 4 cycles after
 the access to $F0xx.
  >>

OK, lets look at the following

cmp 1000
nop
lda (2000),y   // don't worry about the nonsense addresses
                    // at location 2000 is 1234 stored
                    // y=6

is that like a BASIC:

poke 0,2000
poke 0,2006
poke 0,1240    (that's what I do now, it 'seems' to be OK)
?

<< 
 Also you should keep in mind, that the controll byte at $FFF8 allways is
 write enabled.

Does that mean, that every access to $fff8 is allways a write?
(I'm sure that I haven't implemented that yet...)


 
 >PS. My stella now runs Frogger, Dragonstomper, Rabbit and a few others
 >       It doesn't run (well) Suicide Mission, Phasor Patrol, Communists...
 
 Does this include the load capability of Dragonstomper or do you mean only
 the first part?
 
 Ciao, Eckhard Stolberg
  >>

Well, I haven't played Dragonstomper till it loaded another part, but I'd
guess that
it works OK, since survival island works...



<< 
 Again intructions don't matter. The value is stored to the address that is
 accessed 3 or 4 processor cycles after the access to $F0xx. I am not sure
 about the timing though. But indirect accesses work too and they first have
 to read the address from the zeropage, which takes some cycles. Also in my
 programm I have to put a NOP between the two accesses, like
  >>

Does that mean, that the address has to follow after a certain number of
cycles?

I mean, if I insert 100 NOPs after a 'lda RAM', that a 'cmp f123' wouldn't be
a poke anymore?
(I certainly haven't included cycle counters for RAM access yet!)



Thanks and bye

Chris


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