nesemu/cpu/memory.c

//
// Created by william on 10/15/23.
//

#include <assert.h>
#include "log.h"
#include "memory.h"
#include "../include/rom.h"

#define RAM_MAX_ADDR 0x2000
#define RAM_BANK_SIZE 0x800
#define PPU_MAX_ADDR 0x4000
#define PPU_BANK_SIZE 0x8
#define APU_MAX_ADDR 0x4020
#define MAX_ADDR 0xffff

byte mem_get_byte(System *system, address addr) {
    assert(addr <= MAX_ADDR);

    if (addr >= RAM_MAX_ADDR && addr < PPU_MAX_ADDR) {
        byte reg = (addr - RAM_MAX_ADDR) % PPU_BANK_SIZE;
        ppu_read_register(&system->ppu, reg);
        return system->ppu.registers[reg];
    }

    if (addr >= PPU_MAX_ADDR && addr < APU_MAX_ADDR) {
        byte apu_addr = addr - PPU_MAX_ADDR;
        return system->apu_registers[apu_addr];
    }

    return system->ram[addr];
}

word mem_get_word(System *system, address addr) {
    assert(addr < MAX_ADDR);

    if (addr >= RAM_MAX_ADDR && addr < APU_MAX_ADDR) {
        assert(false);
    }

    word word = system->ram[addr];
    word += system->ram[addr + 1] << 8;    // Little endian
    return word;
}

void mem_set_byte(System *system, address addr, byte byte) {
    assert(addr < MAX_ADDR);

    log_trace("Writing '%02x' to address 0x%04x", byte, addr);

    if (addr < RAM_MAX_ADDR) {
        address init_ram_addr = addr % RAM_BANK_SIZE;

        // The value must also be cloned in the three mirrors
        for (int i = 0; i < 4; i++) {
            address ram_addr = init_ram_addr + RAM_BANK_SIZE * i;
            system->ram[ram_addr] = byte;
        }
    } else if (addr < PPU_MAX_ADDR) {
        address reg_addr = (addr - RAM_MAX_ADDR) % PPU_BANK_SIZE;

        int bank_count = (PPU_MAX_ADDR - RAM_MAX_ADDR) / PPU_BANK_SIZE;
        for (int i = 0; i < bank_count; i++) {
            address ram_addr = reg_addr + PPU_BANK_SIZE * i;
            system->ppu.registers[ram_addr] = byte;
        }

        ppu_write_register(&system->ppu, reg_addr);
    } else {
        system->ram[addr] = byte;

        if (addr == PPU_REGISTER_OAM_DMA_ADDR) {
            // Writing to this address triggers an upload to the PPU memory
            system->cpu.oam_dma_triggered = true;
        }
    }
}