Re: [stella] Supercharger strangeness

Subject: Re: [stella] Supercharger strangeness
From: "Frank Palazzolo" <palazzol@xxxxxxxx>
Date: Sat, 5 Aug 2000 11:41:52 -0400
> >It seems to be related to the placement of instructions in the bank 
> >switch code. ???
> Like putting that code in the $F0xx area? ;-)
> When SC writing is enabled, an access to an address in the $F0xx page
> might trigger a write to an address a couple of address changes later.
> If you execute the bankswitching code in the $F0xx page, accesses to
> $FFF8 will take the value to be written from the last address that was
> accessed in $F0xx. So depending on which address you put the STA $FFF8 at,
> the last fetch when the processor reads that instuction might be on
> an address which has the bits set for a working bankswitching/write-enable
> value or not. In general it's best not to execute any code at $F0xx while
> SC writing is enabled.

Looks like you nailed it - thank you!  Although...even if I never turn 
RAM writing on, it still seems to be a problem. So, I guess the 
resetting of the bank can happen on an instruction fetch from the 
$F0xx area, even if supercharger RAM is disabled.  

This seems like an important safety tip...after all, that's 1/16th of 
your ROM space where the bankswitch code is forbidden ;-)


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