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Document quite a bit more, to refresh my memory.

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This commit is contained in:
Thomas Harte 2023-01-10 14:40:03 -05:00
parent dbff7592f5
commit 73549eb38c
2 changed files with 41 additions and 7 deletions
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44
Machines/MSX/MSX.cpp
View File

@ -384,7 +384,9 @@ class ConcreteMachine:
assert(size_t(destination_address) + length <= 65536);
for(std::size_t c = 0; c < (length >> 13); ++c) {
if(memory_slots_[slot].wrapping_strategy == ROMSlotHandler::WrappingStrategy::Repeat) source_address %= memory_slots_[slot].source.size();
if(memory_slots_[slot].wrapping_strategy == ROMSlotHandler::WrappingStrategy::Repeat) {
source_address %= memory_slots_[slot].source.size();
}
memory_slots_[slot].read_pointers[(destination_address >> 13) + c] =
(source_address < memory_slots_[slot].source.size()) ? &memory_slots_[slot].source[source_address] : unpopulated_;
source_address += 8192;
@ -764,27 +766,59 @@ class ConcreteMachine:
i8255PortHandler i8255_port_handler_;
AYPortHandler ay_port_handler_;
/// The current primary slot selection; retains whatever value was written
/// last to the 8255 PPI via port A8.
uint8_t paged_memory_ = 0;
// Divides the current 64kb address space into 8kb chunks.
// 8kb resolution is used by some cartride titles.
uint8_t *read_pointers_[8];
uint8_t *write_pointers_[8];
struct MemorySlots {
/// Optionally attaches non-default logic to any of the four things selectable
/// via the primary slot register.
///
/// Tracks secondary and game-specific paging within each slot.
///
/// Standard MSX assignments:
/// 0 = ROM;
/// 3 = RAM.
///
/// Additional assignments customarily used by this emulator:
/// 1 = any inserted cartridge;
/// 2 = the disk ROM, if present.
struct MemorySlot {
// Each slot may be visible for any number of quarters of the memory map;
// these are the read and write pointers that should appear in the main
// memory map if this slot is visible there.
uint8_t *read_pointers[8];
uint8_t *write_pointers[8];
/// Sets the handler that will be provided with @c run_for and @c read or @c write calls
/// for memory accesses **anywhere it has left memory unmapped**. Anywhere that can be
/// described just in terms of standard memory access read and write destinations should be,
/// ideally to avoid virtual dispatch.
void set_handler(ROMSlotHandler *slot_handler) {
handler.reset(slot_handler);
wrapping_strategy = handler->wrapping_strategy();
}
std::unique_ptr<ROMSlotHandler> handler;
std::vector<uint8_t> source;
HalfCycles cycles_since_update;
std::unique_ptr<ROMSlotHandler> handler;
ROMSlotHandler::WrappingStrategy wrapping_strategy = ROMSlotHandler::WrappingStrategy::Repeat;
} memory_slots_[4];
/// Per-slot storage, as a convenience.
std::vector<uint8_t> source;
};
MemorySlot memory_slots_[4];
/// Base RAM.
uint8_t ram_[65536];
/// A never-read area that writes for unmapped regions can be diverted to.
uint8_t scratch_[8192];
/// A never-written area that reads for unmapped regions can be sourced from.
uint8_t unpopulated_[8192];
HalfCycles time_since_ay_update_;

4
Machines/MSX/ROMSlotHandler.hpp
View File

@ -56,9 +56,9 @@ class ROMSlotHandler {
virtual uint8_t read([[maybe_unused]] uint16_t address) { return 0xff; }
enum class WrappingStrategy {
/// Repeat causes all accesses to be modulo the size of the ROM.
/// All accesses are modulo the size of the ROM.
Repeat,
/// Empty causes all out-of-bounds accesses to read a vacant bus.
/// Out-of-bounds accesses read a vacant bus.
Empty
};