Procházet zdrojové kódy

Implement memory reads, writes.

master
Ben Kurtovic před 9 roky
rodič
revize
5c16f4fad3
1 změnil soubory, kde provedl 41 přidání a 5 odebrání
  1. +41
    -5
      src/mmu.c

+ 41
- 5
src/mmu.c Zobrazit soubor

@@ -84,16 +84,37 @@ void mmu_power(MMU *mmu)
map_slot(mmu, slot, slot);

memset(mmu->system_ram, 0xFF, MMU_SYSTEM_RAM_SIZE);
// TODO: set system_ram to correct values at 0xFFFC-0xFFFF
}

/*
Read a byte from a memory bank, or return 0xFF if the bank is not mapped.
*/
static inline uint8_t bank_byte_read(const uint8_t* bank, uint16_t addr)
{
return bank ? bank[addr] : 0xFF;
}

/*
Read a byte of memory from the given address.

Memory region information is based on:
- http://www.smspower.org/Development/MemoryMap
- http://www.smspower.org/Development/Mappers
*/
uint8_t mmu_read_byte(MMU *mmu, uint16_t addr)
{
// TODO
return 0x00;
if (addr < 0x0400) // First kilobyte is unpaged, for interrupt handlers
return bank_byte_read(mmu->rom_banks[0], addr);
else if (addr < 0x4000) // Slot 0 (0x0400 - 0x3FFF)
return bank_byte_read(mmu->map_slots[0], addr);
else if (addr < 0x8000) // Slot 1 (0x4000 - 0x7FFF)
return bank_byte_read(mmu->map_slots[1], addr - 0x4000);
else if (addr < 0xC000) // Slot 2 (0x8000 - 0xBFFF)
return bank_byte_read(mmu->map_slots[2], addr - 0x8000);
else if (addr < 0xE000) // System RAM (0xC000 - 0xDFFF)
return mmu->system_ram[addr - 0xC000];
else // System RAM, mirrored (0xE000 - 0xFFFF)
return mmu->system_ram[addr - 0xE000];
}

/*
@@ -104,6 +125,21 @@ uint8_t mmu_read_byte(MMU *mmu, uint16_t addr)
*/
bool mmu_write_byte(MMU *mmu, uint16_t addr, uint8_t value)
{
// TODO
return true;
if (addr < 0xC000) { // TODO: implement writes to on-cartridge RAM
return false;
} else if (addr < 0xE000) { // System RAM (0xC000 - 0xDFFF)
mmu->system_ram[addr - 0xC000] = value;
return true;
} else { // System RAM, mirrored (0xE000 - 0xFFFF)
if (addr == 0xFFFC) {
// TODO: handle cartridge RAM mapping control
} else if (addr == 0xFFFD)
map_slot(mmu, 0, value & 0x3F);
else if (addr == 0xFFFE)
map_slot(mmu, 1, value & 0x3F);
else if (addr == 0xFFFF)
map_slot(mmu, 2, value & 0x3F);
mmu->system_ram[addr - 0xE000] = value;
return true;
}
}

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