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Added double buffering ish.

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This commit is contained in:
Marc Parsons
2026-05-21 17:25:57 +01:00
parent 9316a16ab9
commit cca1abf0be
3 changed files with 202 additions and 166 deletions
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185
Core/Memory/SmsMemoryBus.cs
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@@ -42,41 +42,80 @@ namespace Core.Memory
public byte Read(ushort address)
{
if (address < 0x4000) // ROM Slot 0 (0x0000 - 0x3FFF)
if (address < 0x4000)
{
// SMS Hardware Quirk: The first 1KB (0x0000 - 0x03FF) is NEVER paged.
if (address < 0x0400) return ReadFromCartridge(0, address);
return ReadFromCartridge(_romBank0, address);
}
if (address < 0x8000) // ROM Slot 1 (0x4000 - 0x7FFF)
{
return ReadFromCartridge(_romBank1, address & 0x3FFF);
}
if (address < 0xC000) // ROM Slot 2 (0x8000 - 0xBFFF)
{
// --- THE MISSING LINK: Read from Save RAM if enabled! ---
if ((_mapperControl & 0x08) != 0)
if (address < 0x0400)
{
int ramBank = (_mapperControl & 0x04) != 0 ? 1 : 0;
int ramOffset = (ramBank * 0x4000) + (address & 0x1FFF);
return _cartridgeRam[ramOffset];
return _cartridgeRom[address];
}
// Otherwise, read from the ROM as usual
return ReadFromCartridge(_romBank2, address & 0x3FFF);
// Slot 0
return _cartridgeRom[(_romBank0 * 0x4000) + address];
}
if (address < 0x8000)
{
// Slot 1
return _cartridgeRom[(_romBank1 * 0x4000) + (address - 0x4000)];
}
if (address < 0xC000)
{
// Slot 2 (Or SRAM)
if (SramUsed && (_mapperControl & 0x08) != 0)
return _cartridgeRam[address - 0x8000];
else
return _cartridgeRom[(_romBank2 * 0x4000) + (address - 0x8000)];
}
// System RAM (0xC000 - 0xFFFF)
// THE FIX 1: Bitwise AND perfectly forces 0xE000-0xFFFF to mirror down to 0xC000!
return _workRam[address & 0x1FFF];
}
public void Write(ushort address, byte value)
{
if (address < 0x8000) return; // Cannot write to physical ROM
if (address < 0xC000)
{
if (SramUsed && (_mapperControl & 0x08) != 0)
_cartridgeRam[address - 0x8000] = value;
return;
}
// THE FIX 1: Save to RAM using the mirror mask
_workRam[address & 0x1FFF] = value;
// THE FIX 2: Mapper Control Registers live at the very end of the mirrored RAM!
if (address >= 0xFFFC)
{
// Calculate the absolute maximum number of banks inside the currently loaded ROM
int totalBanks = _cartridgeRom.Length / 0x4000;
// Safety catch for empty slots
if (totalBanks == 0) totalBanks = 1;
if (address == 0xFFFC)
{
_mapperControl = value;
}
else if (address == 0xFFFD)
{
_romBank0 = value % totalBanks; // Force the bank to stay inside the array bounds!
}
else if (address == 0xFFFE)
{
_romBank1 = value % totalBanks;
}
else if (address == 0xFFFF)
{
_romBank2 = value % totalBanks;
}
}
}
//public byte Read(ushort address)
//{
// if (address < 0x4000) // ROM Slot 0 (0x0000 - 0x3FFF)
// {
// // SMS Hardware Quirk: The first 1KB (0x0000 - 0x03FF) is NEVER paged.
// // It is hardwired to Bank 0 so the interrupt handlers don't crash.
// if (address < 0x0400) return ReadFromCartridge(0, address);
// return ReadFromCartridge(_romBank0, address);
@@ -87,103 +126,73 @@ namespace Core.Memory
// }
// if (address < 0xC000) // ROM Slot 2 (0x8000 - 0xBFFF)
// {
// // Check if Cartridge RAM is enabled (Bit 3 of Mapper Control)
// // --- THE MISSING LINK: Read from Save RAM if enabled! ---
// if ((_mapperControl & 0x08) != 0)
// {
// // Bit 2 decides if we read the first 16KB half or the second 16KB half of the RAM chip
// int ramBank = (_mapperControl & 0x04) != 0 ? 1 : 0;
// int ramOffset = (ramBank * 0x4000) + (address & 0x3FFF);
// int ramOffset = (ramBank * 0x4000) + (address & 0x1FFF);
// return _cartridgeRam[ramOffset];
// }
// // Otherwise, read from the ROM as usual
// return ReadFromCartridge(_romBank2, address & 0x3FFF);
// }
// // If we are here, we are in System RAM (0xC000 - 0xFFFF)
// // The & 0x1FFF handles the 8KB mirroring automatically!
// // System RAM (0xC000 - 0xFFFF)
// return _workRam[address & 0x1FFF];
//}
//public void Write(ushort address, byte value)
//{
// // --- 1. CARTRIDGE RAM (Save Data) ---
// if (address < 0xC000)
// {
// // Bypass the lock if they are trying to save their game!
// if (address >= 0x8000 && (_mapperControl & 0x08) != 0)
// {
// SramUsed = true;
// int ramBank = (_mapperControl & 0x04) != 0 ? 1 : 0;
// int ramOffset = (ramBank * 0x4000) + (address & 0x3FFF);
// int ramOffset = (ramBank * 0x4000) + (address & 0x1FFF);
// _cartridgeRam[ramOffset] = value;
// return;
// }
// // You cannot write to a ROM cartridge!
// return;
// }
// // --- 2. SYSTEM RAM ---
// // Write to System RAM
// _workRam[address & 0x1FFF] = value;
// // --- 3. SEGA MAPPER (With Hardware Mirroring!) ---
// // By checking the masked address (address & 0x1FFF), we perfectly
// // catch writes to 0xFFFC-0xFFFF *and* their 0xDFFC-0xDFFF mirrors!
// int mapperAddress = address & 0x1FFF;
// // --- THE SEGA MAPPER ---
// if (address == 0xFFFC) // <-- ADD THIS
// {
// _mapperControl = value;
// }
// else if (address == 0xFFFD)
// {
// _romBank0 = value;
// }
// if (mapperAddress == 0x1FFC) _mapperControl = value;
// else if (mapperAddress == 0x1FFD) _romBank0 = value;
// else if (mapperAddress == 0x1FFE) _romBank1 = value;
// else if (mapperAddress == 0x1FFF) _romBank2 = value;
// // Write to System RAM
// _workRam[address & 0x1FFF] = value;
// // --- THE SEGA MAPPER ---
// // If the CPU wrote to the very top of memory, it is commanding a bank swap!
// if (address == 0xFFFD)
// {
// _romBank0 = value;
// }
// else if (address == 0xFFFE)
// {
// _romBank1 = value;
// }
// else if (address == 0xFFFF)
// {
// _romBank2 = value;
// }
//}
public void Write(ushort address, byte value)
{
if (address < 0xC000)
{
// Bypass the lock if they are trying to save their game!
if (address >= 0x8000 && (_mapperControl & 0x08) != 0)
{
SramUsed = true;
int ramBank = (_mapperControl & 0x04) != 0 ? 1 : 0;
int ramOffset = (ramBank * 0x4000) + (address & 0x1FFF);
_cartridgeRam[ramOffset] = value;
return;
}
// You cannot write to a ROM cartridge!
return;
}
// Write to System RAM
_workRam[address & 0x1FFF] = value;
// --- THE SEGA MAPPER ---
if (address == 0xFFFC) // <-- ADD THIS
{
_mapperControl = value;
}
else if (address == 0xFFFD)
{
_romBank0 = value;
}
// Write to System RAM
_workRam[address & 0x1FFF] = value;
// --- THE SEGA MAPPER ---
// If the CPU wrote to the very top of memory, it is commanding a bank swap!
if (address == 0xFFFD)
{
_romBank0 = value;
}
else if (address == 0xFFFE)
{
_romBank1 = value;
}
else if (address == 0xFFFF)
{
_romBank2 = value;
}
}
private byte ReadFromCartridge(int bankIndex, int offset)
{
if (!_isCartridgeLoaded) return 0xFF; // Floating bus if no game