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Improves exposition, eliminates a couple of redundant map adjustments.

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This commit is contained in:
Thomas Harte 2020-11-30 18:07:03 -05:00
parent 5cb4077576
commit 87069da3dd
1 changed files with 24 additions and 4 deletions
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28
Machines/Apple/AppleIIgs/MemoryMap.hpp
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@ -242,6 +242,10 @@ class MemoryMap {
// MARK: - Memory banking.
// Cf. LanguageCardSwitches; this function should update the region from
// $D000 onwards as per the state of the language card flags — there may
// end up being ROM or RAM (or auxiliary RAM), and the first 4kb of it
// may be drawn from either of two pools.
void set_language_card_paging() {
const auto language_state = language_card_.state();
const auto zero_state = auxiliary_switches_.zero_state();
@ -294,6 +298,14 @@ class MemoryMap {
apply(0xe100, e0_ram);
}
// Cf. AuxiliarySwitches; this should establish whether ROM or card switches
// are exposed in the distinct regions C100–C2FF, C300–C3FF, C400–C7FF and
// C800–CFFF.
//
// On the IIgs it intersects with the current shadow register.
//
// TODO: so... shouldn't the card mask be incorporated here? I've got it implemented
// distinctly at present, but does that create any invalid state interactions?
void set_card_paging() {
const bool inhibit_banks0001 = shadow_register_ & 0x40;
const auto state = auxiliary_switches_.card_state();
@ -357,18 +369,24 @@ class MemoryMap {
apply(0xe100);
}
// Cf. LanguageCardSwitches; this should update whether base or auxiliary RAM is
// visible in: (i) the zero and stack pages; and (ii) anywhere that the language
// card is exposing RAM instead of ROM.
void set_zero_page_paging() {
// Affects bank $00 only, and should be a single region.
auto &region = regions[region_map[0]];
region.read = region.write = auxiliary_switches_.zero_state() ? &ram_base[0x10000] : ram_base;
assert(region_map[0x0000]+1 == region_map[0x0002]);
// Switching to or from auxiliary RAM potentially affects the language
// and regular card areas.
set_card_paging();
// Switching to or from auxiliary RAM potentially affects the
// language card area.
set_language_card_paging();
}
// IIgs specific: sets or resets the ::IsShadowed flag across affected banks as
// per the current state of the shadow register.
//
// Completely distinct from the auxiliary and language card switches.
void set_shadowing() {
const bool inhibit_all_pages = !(speed_register_ & 0x10);
@ -455,6 +473,8 @@ class MemoryMap {
#undef apply
}
// Cf. the AuxiliarySwitches; establishes whether main or auxiliary RAM
// is exposed in bank $00 for a bunch of regions.
void set_main_paging() {
const auto state = auxiliary_switches_.main_state();
@ -474,10 +494,10 @@ class MemoryMap {
// This also affects shadowing flags, if shadowing is enabled at all,
// and might affect RAM in the IO area of bank $00 because the language
// card can be inhibited on a IIgs.
set_shadowing();
set_card_paging();
}
// Throwaway storage to facilitate branchless handling of shadowing.
uint8_t shadow_throwaway_;
public: