Subject: Re: [stella] A new way to bankswitch From: "Fred Quimby" <c9r@xxxxxxxxxxx> Date: Wed, 9 Mar 2005 18:16:03 -0500 |
>I don't agree on that. Look at the timing diagram for an LDA $FFF8: > > # address R/W description > --- ------- --- ------------------------------------------ > 1 PC R fetch opcode, increment PC > 2 PC R fetch low byte of address, increment PC > 3 PC R fetch high byte of address, increment PC > 4 address R read from effective address > >When the LDA $FFF8 is executed, you only have the effective adress >on the bus for one processor cycle. So If the bankswitching hardware does >not switch, if it sees a valid adress for one cycle, it will simply not >work >at all :-) > >And the 0.1 5F Cap is good for about 3005s delay. I think I calculated that >a while ago. >Don't know the exact value, but it is in that range. It should switch ! I assume you mean 300 ns... But anyway, I didn't realize that it would operate that fast with a cap. That short of a delay should allow a switch to complete within a single cycle, so if true, I wonder if it would work in a 16k scheme, where we could place something like this in every bank: ORG $FFF5 Bank_0: RTS Bank_1: RTS Bank_2: RTS Bank_3: RTS Then to jump to a routine in a particular bank, just do the LDA/PHA thing, then JMP Bank_X. If it works, it would really reduce the complexity of writing a 16k (or larger) game. OK, so maybe I should wait for this to be thoroughly tested before I get too excited. Archives (includes files) at http://www.biglist.com/lists/stella/archives/ Unsub & more at http://stella.biglist.com
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