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_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 ram[RAM_SIZE];

byte mem_get_byte(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_sig_read_register(reg);
    }

    return ram[addr];
}

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

    return &ram[addr];
}

word mem_get_word(address addr) {
    assert(addr < MAX_ADDR);

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

void mem_set_byte(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;
            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 + RAM_MAX_ADDR;
            ram[ram_addr] = byte;
        }

        ppu_sig_write_register(reg_addr);
    } else {
        ram[addr] = byte;

        if (addr == PPU_REGISTER_OAM_DMA_ADDR) {
            // Writing to this address triggers an upload to the PPU memory
            cpu_trigger_oam_dma();
        }
    }
}