nesemu/mappers/nrom.c

#include "../include/mapper.h"
#include "../include/rom.h"
#include "../cpu/memory.h"

#define PRG_BANK_SIZE 0x4000    // 16Kb

byte *nrom_mem_read(address addr) {
    Rom *rom = rom_get();

    if (addr < PRG_BANK_SIZE || rom->prg_rom_size > PRG_BANK_SIZE) {
        return &rom->prg_rom[addr];
    }

    // The second bank is mirrored
    return &rom->prg_rom[addr - PRG_BANK_SIZE];
}

byte *nrom_ppu_read(address addr) {
    if (addr < 0x2000) {
        Rom *rom = rom_get();
        return &rom->chr_rom[addr];
    }

    return NULL;
}

Mapper get_simple_mapper() {
    Mapper mapper;
    mapper.mem_read = &nrom_mem_read;
    mapper.ppu_read = &nrom_ppu_read;
    return mapper;
}