Subject: Re: [stella] Parker Brother's E0 Bankswitching From: Adam Wozniak <adam@xxxxxxxxxxxxxxxx> Date: Fri, 25 Apr 2003 09:09:48 -0700 (PDT) |
On Fri, 25 Apr 2003, Joe Grand wrote: > Hey everyone. I've been trying to figure out E0 bankswitching for a little > while now (from the cartridge side, not the programmer side). I read > through Kevin Horton's sizes.txt file and Thomas' good explanation > (http://www.biglist.com/lists/stella/archives/200211/msg00125.html), but > what I can't figure out is it seems to me like the currently selected > slice/segment relationship needs to be remembered by the cartridge until > the slice is changed for that particular segment (using one of the 24 > hotspots, LDA $1FE0, etc.) > > From a programmer point-of-view, apparently this requires less overhead to > keep track of what bank you are currently in (compared to something more > standard like F6, F8, etc.), but I don't quite see that, since it seems > that the programmer will need to keep track of which slice is currently > "loaded" into each segment. > > The way I'm seeing it, if someone did a: > > LDA $1FE0 > LDA $1FE8 > LDA $1FF0 > > then slice 0 (0000-03FF) will be mapped to each of the 3 segments > (1000-13FF for segment #0, 1400-17FF for segment #1, 1800-1BFF for segment > #2). Why would something like that ever want to be done? > > And then, the memory map will stay as above until someone later on in the > code does a LDA $1FE9, for example, and then slice 1 (0400-07FF) would be > mapped into segment #1 (keeping the mappings of segment #0 and segment #2 > untouched)? > > Can someone clarify this for me? I confuse myself more the longer I look at > this stuff.. I'm trying to figure out if I can do this with simple > programmable logic or if I have to use some gates as registers to store the > current state of each mapped segment, which would be a bummer. You seem to have the right idea. It shouldn't be that hard to implement in VHDL on a CPLD. -- adam@xxxxxxxxxxxxxxxx http://cuddlepuddle.org/~adam/pgp.html Will code for food. http://cuddlepuddle.org/~adam/resume.html "Fools despise wisdom and instruction." Proverbs 1:7 ---------------------------------------------------------------------------------------------- Archives (includes files) at http://www.biglist.com/lists/stella/archives/ Unsub & more at http://www.biglist.com/lists/stella/
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