nesemu/rom/ines.c

//
// Created by william on 12/2/23.
//

#include <stdbool.h>
#include <stdio.h>
#include "log.h"
#include "../include/rom.h"
#include "../include/system.h"

// Flag 6
#define NES_HEADER_FLAG_MIRRORING 0x01
#define NES_HEADER_FLAG_BATTERY 0x02
#define NES_HEADER_FLAG_TRAINER 0x04
#define NES_HEADER_FLAG_IGNORE_MIRRORING 0x08
// Lower nybble of mapper number
#define NES_HEADER_FLAG_LOWER_MAPPER_NUMBER 0xf0

// Flag 7
#define NES_HEADER_FLAG_VS_UNISYSTEM 0x01
#define NES_HEADER_FLAG_PLAYCHOICE_10 0x02
// Upper nybble of mapper number, not used in iNes 1.0 format
#define NES_HEADER_FLAG_UPPER_MAPPER_NUMBER 0xf0

// Flag 9
#define NES_HEADER_FLAG_TV_SYSTEM 0x01

// Flag 10
#define NES_HEADER_FLAG_PRG_RAM 0x10
#define NES_HEADER_FLAG_BUS_CONFLICT 0x20

struct INesHeaderFlags {
/* Mirroring: 0: horizontal (vertical arrangement) (CIRAM A10 = PPU A11)
              1: vertical (horizontal arrangement) (CIRAM A10 = PPU A10) */
    bool nametable_mirrored;
// 1: Ignore mirroring control or above mirroring bit; instead provide four-screen VRAM
    bool ignore_mirroring;
// 1: Cartridge contains battery-backed PRG RAM ($6000-7FFF) or other persistent memory
    bool has_battery;
// 1: 512-byte trainer at $7000-$71FF (stored before PRG data)
    bool has_trainer;
    bool vs_unisystem;
// PlayChoice-10 (8 KB of Hint Screen data stored after CHR data)
    bool playchoice_10;
    bool tv_system;
    bool has_prg_ram;
    bool has_bus_conflict;
};

typedef struct {
    // PRG ROM size in 16KB units
    unsigned char prg_rom_size;
    unsigned char prg_ram_size;
    // CHR ROM size in 8KB units
    unsigned char chr_rom_size;
    unsigned char mapper_number;
    struct INesHeaderFlags flags;
} INesHeader;

bool rom_is_ines(const char header[16]) {
    return header[0] == 'N' && header[1] == 'E' && header[2] == 'S';
}

INesHeader read_header(const char header_buf[16]) {
    INesHeader header;

    unsigned char flag6 = header_buf[6];
    unsigned char flag7 = header_buf[7];
    unsigned char flag9 = header_buf[9];
    unsigned char flag10 = header_buf[10];

    header.flags.nametable_mirrored = flag6 & NES_HEADER_FLAG_MIRRORING;
    header.flags.ignore_mirroring = flag6 & NES_HEADER_FLAG_IGNORE_MIRRORING;
    header.flags.has_battery = flag6 & NES_HEADER_FLAG_BATTERY;
    header.flags.has_trainer = flag6 & NES_HEADER_FLAG_TRAINER;
    header.flags.vs_unisystem = flag7 & NES_HEADER_FLAG_VS_UNISYSTEM;
    header.flags.playchoice_10 = flag7 & NES_HEADER_FLAG_PLAYCHOICE_10;
    header.flags.tv_system = flag9 & NES_HEADER_FLAG_TV_SYSTEM;
    header.flags.has_prg_ram = flag10 & NES_HEADER_FLAG_PRG_RAM | 0x01;
    header.flags.has_bus_conflict = flag10 & NES_HEADER_FLAG_BUS_CONFLICT;

    header.prg_rom_size = header_buf[4];
    header.prg_ram_size = header_buf[8];
    header.chr_rom_size = header_buf[5];
    header.mapper_number = (flag6 & NES_HEADER_FLAG_LOWER_MAPPER_NUMBER) >> 4;

    if (!header.prg_ram_size) {
        // For compatibility, a value of 0 unit of PRG RAM infers 8KB, or 1 unit.
        header.prg_ram_size = 1;
    }

    log_debug("=== iNes ROM Header ===");
    log_debug("PRG: %dx16KB (ROM), %dx8KB (RAM)",
              header.prg_rom_size,
              header.prg_ram_size);
    log_debug("CHR: %dx8KB (ROM)",
              header.chr_rom_size);
    log_debug("Mapper number: %d",
              header.mapper_number);
    log_debug("Nametable mirrored: %d", header.flags.nametable_mirrored);
    log_debug("Ignore mirroring: %d", header.flags.ignore_mirroring);
    log_debug("Has PRG RAM: %d", header.flags.has_prg_ram);
    log_debug("Has bus conflict: %d", header.flags.has_bus_conflict);
    log_debug("Has battery: %d", header.flags.has_battery);
    log_debug("Has trainer: %d", header.flags.has_trainer);
    log_debug("VS Unisystem: %d", header.flags.vs_unisystem);
    log_debug("Playchoice 10: %d", header.flags.playchoice_10);
    log_debug("TV System: %d", header.flags.tv_system);

    return header;
}

bool rom_ines_read_trainer(FILE *file, INesHeader *header) {
    if (!header->flags.has_trainer) {
        log_debug("ROM does not contains trainer");
        return true;
    }

    // We don't support the trainer, so we skip ahead instead.
    if (fseek(file, ROM_TRAINER_SIZE, SEEK_CUR)) {
        log_debug("ROM has trainer, skipping %d bytes", ROM_TRAINER_SIZE);
        return true;
    }

    log_error("Failed to skip trainer");
    return false;
}

bool rom_ines_read_prg_rom(FILE *file, INesHeader *header, System *system) {
    unsigned int prg_rom_size = header->prg_rom_size * 16384;
    log_debug("Reading %d bytes PRG ROM", prg_rom_size);

    if (fread(&system->ram[system->mapper.prg_rom_start_addr], sizeof(byte), prg_rom_size, file) < prg_rom_size) {
        log_error("Failed to read PRG ROM");
        return false;
    }

    system->mapper.post_prg_load(&system->ram[0], header->prg_rom_size);

    return true;
}

bool rom_ines_read_chr_rom(FILE *file, INesHeader *header, System *system) {
    if (header->chr_rom_size <= 0) {
        log_debug("No CHR ROM to read");
        return true;
    }

    unsigned int chr_rom_size = header->chr_rom_size * 8192;
    log_debug("Reading %d bytes CHR ROM", chr_rom_size);

    if (fread(system->ppu.vram, sizeof(byte), chr_rom_size, file) < chr_rom_size) {
        log_error("Failed to read CHR ROM");
        return false;
    }

    return true;
}

bool rom_ines_read(const char header_buf[ROM_HEADER_SIZE], FILE *file, System *system) {
    INesHeader header = read_header(header_buf);
    system->rom_header = &header;

    return rom_ines_read_trainer(file, &header) &&
           rom_ines_read_prg_rom(file, &header, system) &&
           rom_ines_read_chr_rom(file, &header, system);
}