Subject: Re: [stella] Supercharger Bankswitches and RAM access! From: Eckhard_Stolberg@xxxxxxxxxxxxxxxxxxxxx (Eckhard Stolberg) Date: Sat, 15 Mar 1997 14:37:12 +0100 |
I should have send this to the group instead of email! >I need to know what kind of instructions will be used for value >specification, >so far I take absolut, absolut-x, absolut-y, indirect-x and indirect-y. Instructions don't matter. All accesses of addresses between $F000 and $F100 cause an internal write register to be set to: accessed address minus $F000. >What kind of instructions will be used for poking? >(absolut, absolut-x, absolut-y, indirect-x and indirect-y) >I know for sure CMP,AND,BIT,LDA, are there any others? 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 CMP $F000,X NOP CMP $FFF8 or otherwise the programm would crash, because it writes to a wrong address. >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. >Which instruction preserve the value, which instructions don't? >(All implied instruction?) (for sure I know: NOP,TAX,TAY) I don't know for sure, but I think, that the Supercharger behaves as if an address containing $00 was accessed by the intruction, that caused the write. So all registers and flags should be set accordingly. >Since address fields below 0xf000 initiate a poke, what about addresses in >that >region that are poked to, is it possible, if so can a poke follow directly? I don't know if it is possiblbe, but I think it is unwise to try it, because the access that finishes the write would initiate another write. Also you should keep in mind, that the controll byte at $FFF8 allways is write enabled. >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 p.s.: This is only my theory about how the writing mechanism works. Please correct me, if I am wrong. -- Archives available at http://www.biglist.com/lists/stella/archives/ E-mail UNSUBSCRIBE in the body to stella-request@xxxxxxxxxxx to be removed.
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