nesemu/mappers/simple_mapper.c

#include "../include/mapper.h"
#include "../include/rom.h"
#include "../cpu/memory.h"
#include <string.h>

#define SIMPLE_MAPPER_PRG_START_ADDR 0x8000
#define PRG_PART_SIZE 0x4000    // 16Kb

void post_prg_load(unsigned int prg_size) {
    if (prg_size == 2) {
        // The whole space is occupied, nothing to do
        return;
    }

    // We need to mirror the data in the upper ram
    byte *source = mem_get_ptr(SIMPLE_MAPPER_PRG_START_ADDR);
    byte *destination = mem_get_ptr(SIMPLE_MAPPER_PRG_START_ADDR + PRG_PART_SIZE);
    memcpy(destination, source, PRG_PART_SIZE);
}

Mapper get_simple_mapper() {
    Mapper mapper;
    mapper.prg_rom_start_addr = SIMPLE_MAPPER_PRG_START_ADDR;
    mapper.post_prg_load = &post_prg_load;
    return mapper;
}