nesemu/cpu/memory.c

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

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


#define RAM_SIZE 0x0800
#define RAM_MAX_ADDR 0x2000
#define PPU_MAX_ADDR 0x4000
#define APU_MAX_ADDR 0x4020
#define UNMAPPED_MAX_ADDR 0x6000
#define CARTRIDGE_RAM_MAX_ADDR 0x8000
#define MEM_ADDR_MAX 0xffff

byte ram[RAM_SIZE];

byte *mem_get_ptr(address addr) {
    assert(addr <= RAM_MAX_ADDR);

    if (addr < RAM_MAX_ADDR) {
        address ram_addr = addr % RAM_SIZE;   // There is four mirror of RAM
        return &ram[ram_addr];
    }

    // Only supported for RAM
    assert(false);
}

byte mem_get_byte(address addr) {
    assert(addr <= MEM_ADDR_MAX);

    if (addr < RAM_MAX_ADDR) {
        address ram_addr = addr % RAM_SIZE;
        return ram[ram_addr];
    } else if (addr < PPU_MAX_ADDR) {
        address relative_addr = addr - RAM_MAX_ADDR;
        byte ppu_reg = relative_addr % 8;
        return ppu_read_reg(ppu_reg);
    } else if (addr < APU_MAX_ADDR) {
        // TODO NES API and I/O registers
        return 0;
    } else if (addr < UNMAPPED_MAX_ADDR) {
        // Unmapped
        assert(false);
    } else if (addr < CARTRIDGE_RAM_MAX_ADDR) {
        // TODO Cartridge RAM
        return 0;
    } else {
        address rom_addr = addr - CARTRIDGE_RAM_MAX_ADDR;

        Mapper *mapper = system_get_mapper();
        return *(mapper->mem_read(rom_addr));
    }
}

word mem_get_word(address addr) {
    assert(addr <= MEM_ADDR_MAX - 1);

    byte data1;
    byte data2;

    if (addr < RAM_MAX_ADDR - 1) {
        address ram_addr = addr % RAM_SIZE;
        data1 = ram[ram_addr];
        data2 = ram[ram_addr + 1];
    } else if (addr < UNMAPPED_MAX_ADDR) {
        // Unsupported
        assert(false);
    } else if (addr < CARTRIDGE_RAM_MAX_ADDR) {
        // TODO Cartridge RAM
        return 0;
    } else {
        address rom_addr = addr - CARTRIDGE_RAM_MAX_ADDR;

        Mapper *mapper = system_get_mapper();
        byte *location = mapper->mem_read(rom_addr);

        data1 = *location;
        data2 = *(location + 1);
    }

    return data1 + (data2 << 8);
}

void mem_set_byte(address addr, byte data) {
    assert(addr < MEM_ADDR_MAX);

    if (addr < RAM_MAX_ADDR) {
        address ram_addr = addr % RAM_SIZE;
        ram[ram_addr] = data;
    } else if (addr < PPU_MAX_ADDR) {
        address relative_addr = addr - RAM_MAX_ADDR;
        byte ppu_reg = relative_addr % 8;
        ppu_write_reg(ppu_reg, data);
    } else if (addr == PPU_REGISTER_OAM_DMA_ADDR) {
        ppu_write_reg_oam_addr(data);

        // Writing to this address triggers an upload to the PPU memory
        cpu_trigger_oam_dma();
    } else if (addr < APU_MAX_ADDR) {
        // TODO NES API and I/O registers
    } else if (addr < UNMAPPED_MAX_ADDR) {
        // Unmapped
        assert(false);
    } else if (addr < CARTRIDGE_RAM_MAX_ADDR) {
        // TODO Cartridge RAM
    } else {
        // ROM is read-only
        assert(false);
    }
}