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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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Thomas Harte 2020-12-05 19:09:21 -05:00
parent 1422d43c35
commit 55de98fb46
1 changed files with 41 additions and 6 deletions
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47
Machines/Apple/AppleIIgs/MemoryMap.hpp
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@ -61,13 +61,48 @@ class MemoryMap {
// Current beliefs about the IIgs memory map:
//
// * language card banking applies to banks $00, $01, $e0 and $e1;
// * auxiliary memory switches apply to banks $00 only;
// * shadowing may be enabled only on banks $00 and $01, or on all RAM pages.
// * auxiliary memory switches apply to bank $e0 only, but thereby also affect shadowed writes from $00;
// * shadowing may be enabled only on banks $00 and $01, or on all RAM pages; and
// * whether bit 16 of the address is passed to the Mega II is selectable — this affects both the destination
// of odd-bank shadows, and whether bank $e1 is actually distinct from $e0.
//
// So banks $00 and $01 need their own divided spaces at the shadowing resolution,
// all the other fast RAM banks can share a set of divided spaces, $e0 and $e1 need
// to be able to deal with language card-level division but no further, and the pure
// ROM pages don't need to be subdivided at all.
// So:
//
// * banks $00 and $01 need to be divided both by shadowing zones and by the language card;
// * all other fast RAM banks need be divided by shadowing zone only;
// * $e0 needs to be ready for any language/auxiliary arrangement;
// * $e1 needs to apply the language card mapping only; and
// * ROM banks don't need to be divided? Or probably they shadow writes back to $e0/$e1 too?
// Shadowing zones:
//
// $0400–$0800 Text Page 1
// $0800–$0C00 Text Page 2 [ROM 03 machines]
// $2000–$4000 High-res Page 1, and Super High-res in odd banks
// $4000–$6000 High-res Page 2, and Huper High-res in odd banks
// $6000–$a000 Odd banks only, rest of Super High-res
// [plus IO and language card space, subject to your definition of shadowing]
// Language card zones:
//
// $D000–$E000 4kb window, into either bank 1 or bank 2
// $E000–end 12kb window, always the same RAM.
// Auxiliary zones:
//
// $0000–$0200 Zero page (and stack)
// $0200–$0400 [space in between]
// $0400–$0800 Text Page 1
// $0800–$2000 [space in between]
// $2000–$4000 High-res Page 1
// $4000–$C000 [space in between]
// Card zones:
//
// $C100–$C2FF either cards or IIe-style ROM
// $C300–$C3FF IIe-supplied 80-column card replacement ROM
// $C400–$C7FF either cards or IIe-style ROM
// $C800–$CFFF Standard extended card area
// Reserve region 0 as that for unmapped memory.
region();