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Adds a new statement of intent.
Now I need to try to decide whether I like my current all-in-one mapping for shadowing + paging, or whether it's better to split the things. I'm tending towards the latter at least until the functionality works.
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@ -61,13 +61,48 @@ class MemoryMap {
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// Current beliefs about the IIgs memory map:
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// Current beliefs about the IIgs memory map:
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//
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//
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// * language card banking applies to banks $00, $01, $e0 and $e1;
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// * language card banking applies to banks $00, $01, $e0 and $e1;
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// * auxiliary memory switches apply to banks $00 only;
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// * auxiliary memory switches apply to bank $e0 only, but thereby also affect shadowed writes from $00;
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// * shadowing may be enabled only on banks $00 and $01, or on all RAM pages.
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// * shadowing may be enabled only on banks $00 and $01, or on all RAM pages; and
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// * whether bit 16 of the address is passed to the Mega II is selectable — this affects both the destination
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// of odd-bank shadows, and whether bank $e1 is actually distinct from $e0.
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//
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//
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// So banks $00 and $01 need their own divided spaces at the shadowing resolution,
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// So:
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// all the other fast RAM banks can share a set of divided spaces, $e0 and $e1 need
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//
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// to be able to deal with language card-level division but no further, and the pure
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// * banks $00 and $01 need to be divided both by shadowing zones and by the language card;
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// ROM pages don't need to be subdivided at all.
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// * all other fast RAM banks need be divided by shadowing zone only;
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// * $e0 needs to be ready for any language/auxiliary arrangement;
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// * $e1 needs to apply the language card mapping only; and
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// * ROM banks don't need to be divided? Or probably they shadow writes back to $e0/$e1 too?
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// Shadowing zones:
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//
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// $0400–$0800 Text Page 1
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// $0800–$0C00 Text Page 2 [ROM 03 machines]
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// $2000–$4000 High-res Page 1, and Super High-res in odd banks
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// $4000–$6000 High-res Page 2, and Huper High-res in odd banks
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// $6000–$a000 Odd banks only, rest of Super High-res
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// [plus IO and language card space, subject to your definition of shadowing]
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// Language card zones:
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//
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// $D000–$E000 4kb window, into either bank 1 or bank 2
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// $E000–end 12kb window, always the same RAM.
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// Auxiliary zones:
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//
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// $0000–$0200 Zero page (and stack)
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// $0200–$0400 [space in between]
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// $0400–$0800 Text Page 1
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// $0800–$2000 [space in between]
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// $2000–$4000 High-res Page 1
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// $4000–$C000 [space in between]
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// Card zones:
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//
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// $C100–$C2FF either cards or IIe-style ROM
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// $C300–$C3FF IIe-supplied 80-column card replacement ROM
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// $C400–$C7FF either cards or IIe-style ROM
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// $C800–$CFFF Standard extended card area
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// Reserve region 0 as that for unmapped memory.
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// Reserve region 0 as that for unmapped memory.
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region();
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region();
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