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Calculate and verify ROM checksum

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This commit is contained in:
Michael Smith 2025-08-13 13:48:38 +02:00
parent ba4e098ba5
commit c3d17459c6
4 changed files with 32 additions and 326 deletions
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301
cartridge.go
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@ -1,301 +0,0 @@
package main
import (
"bytes"
"encoding/binary"
"io"
"log"
"os"
)
// See https://gbdev.io/pandocs/The_Cartridge_Header.html#0104-0133--nintendo-logo
var expectedLogo = [48]byte{
0xCE, 0xED, 0x66, 0x66, 0xCC, 0x0D, 0x00, 0x0B,
0x03, 0x73, 0x00, 0x83, 0x00, 0x0C, 0x00, 0x0D,
0x00, 0x08, 0x11, 0x1F, 0x88, 0x89, 0x00, 0x0E,
0xDC, 0xCC, 0x6E, 0xE6, 0xDD, 0xDD, 0xD9, 0x99,
0xBB, 0xBB, 0x67, 0x63, 0x6E, 0x0E, 0xEC, 0xCC,
0xDD, 0xDC, 0x99, 0x9F, 0xBB, 0xB9, 0x33, 0x3E,
}
// Cartridge types
// See https://gbdev.io/pandocs/The_Cartridge_Header.html#0147--cartridge-type
var cartridgeTypes = map[byte]string{
0x00: "ROM ONLY",
0x01: "MBC1",
0x02: "MBC1+RAM",
0x03: "MBC1+RAM+BATTERY",
0x05: "MBC2",
0x06: "MBC2+BATTERY",
0x08: "ROM+RAM 9",
0x09: "ROM+RAM+BATTERY 9",
0x0B: "MMM01",
0x0C: "MMM01+RAM",
0x0D: "MMM01+RAM+BATTERY",
0x0F: "MBC3+TIMER+BATTERY",
0x10: "MBC3+TIMER+RAM+BATTERY 10",
0x11: "MBC3",
0x12: "MBC3+RAM 10",
0x13: "MBC3+RAM+BATTERY 10",
0x19: "MBC5",
0x1A: "MBC5+RAM",
0x1B: "MBC5+RAM+BATTERY",
0x1C: "MBC5+RUMBLE",
0x1D: "MBC5+RUMBLE+RAM",
0x1E: "MBC5+RUMBLE+RAM+BATTERY",
0x20: "MBC6",
0x22: "MBC7+SENSOR+RUMBLE+RAM+BATTERY",
0xFC: "POCKET CAMERA",
0xFD: "BANDAI TAMA5",
0xFE: "HuC3",
0xFF: "HuC1+RAM+BATTERY",
}
// RAM sizes
// https://gbdev.io/pandocs/The_Cartridge_Header.html#0149--ram-size
var ramSizes = map[byte]string{
0x00: "0 - No RAM",
0x01: "UNUSED VALUE",
0x02: "8 KiB - 1 bank",
0x03: "32 KiB - 4 banks of 8 KiB each",
0x04: "128 KiB 16 banks of 8 KiB each",
0x05: "64 KiB 8 banks of 8 KiB each",
}
// Old licensees
// https://gbdev.io/pandocs/The_Cartridge_Header.html#014b--old-licensee-code
var oldLicensees = map[byte]string{
0x00: "None",
0x01: "Nintendo",
0x08: "Capcom",
0x09: "HOT-B",
0x0A: "Jaleco",
0x0B: "Coconuts Japan",
0x0C: "Elite Systems",
0x13: "EA (Electronic Arts)",
0x18: "Hudson Soft",
0x19: "ITC Entertainment",
0x1A: "Yanoman",
0x1D: "Japan Clary",
0x1F: "Virgin Games Ltd.3",
0x24: "PCM Complete",
0x25: "San-X",
0x28: "Kemco",
0x29: "SETA Corporation",
0x30: "Infogrames5",
0x31: "Nintendo",
0x32: "Bandai",
0x33: "Indicates that the New licensee code should be used instead.",
0x34: "Konami",
0x35: "HectorSoft",
0x38: "Capcom",
0x39: "Banpresto",
0x3C: "Entertainment Interactive (stub)",
0x3E: "Gremlin",
0x41: "Ubi Soft1",
0x42: "Atlus",
0x44: "Malibu Interactive",
0x46: "Angel",
0x47: "Spectrum HoloByte",
0x49: "Irem",
0x4A: "Virgin Games Ltd.3",
0x4D: "Malibu Interactive",
0x4F: "U.S. Gold",
0x50: "Absolute",
0x51: "Acclaim Entertainment",
0x52: "Activision",
0x53: "Sammy USA Corporation",
0x54: "GameTek",
0x55: "Park Place13",
0x56: "LJN",
0x57: "Matchbox",
0x59: "Milton Bradley Company",
0x5A: "Mindscape",
0x5B: "Romstar",
0x5C: "Naxat Soft14",
0x5D: "Tradewest",
0x60: "Titus Interactive",
0x61: "Virgin Games Ltd.3",
0x67: "Ocean Software",
0x69: "EA (Electronic Arts)",
0x6E: "Elite Systems",
0x6F: "Electro Brain",
0x70: "Infogrames5",
0x71: "Interplay Entertainment",
0x72: "Broderbund",
0x73: "Sculptured Software6",
0x75: "The Sales Curve Limited7",
0x78: "THQ",
0x79: "Accolade15",
0x7A: "Triffix Entertainment",
0x7C: "MicroProse",
0x7F: "Kemco",
0x80: "Misawa Entertainment",
0x83: "LOZC G.",
0x86: "Tokuma Shoten",
0x8B: "Bullet-Proof Software2",
0x8C: "Vic Tokai Corp.16",
0x8E: "Ape Inc.17",
0x8F: "I'Max18",
0x91: "Chunsoft Co.8",
0x92: "Video System",
0x93: "Tsubaraya Productions",
0x95: "Varie",
0x96: "Yonezawa19/S'Pal",
0x97: "Kemco",
0x99: "Arc",
0x9A: "Nihon Bussan",
0x9B: "Tecmo",
0x9C: "Imagineer",
0x9D: "Banpresto",
0x9F: "Nova",
0xA1: "Hori Electric",
0xA2: "Bandai",
0xA4: "Konami",
0xA6: "Kawada",
0xA7: "Takara",
0xA9: "Technos Japan",
0xAA: "Broderbund",
0xAC: "Toei Animation",
0xAD: "Toho",
0xAF: "Namco",
0xB0: "Acclaim Entertainment",
0xB1: "ASCII Corporation or Nexsoft",
0xB2: "Bandai",
0xB4: "Square Enix",
0xB6: "HAL Laboratory",
0xB7: "SNK",
0xB9: "Pony Canyon",
0xBA: "Culture Brain",
0xBB: "Sunsoft",
0xBD: "Sony Imagesoft",
0xBF: "Sammy Corporation",
0xC0: "Taito",
0xC2: "Kemco",
0xC3: "Square",
0xC4: "Tokuma Shoten",
0xC5: "Data East",
0xC6: "Tonkin House",
0xC8: "Koei",
0xC9: "UFL",
0xCA: "Ultra Games",
0xCB: "VAP, Inc.",
0xCC: "Use Corporation",
0xCD: "Meldac",
0xCE: "Pony Canyon",
0xCF: "Angel",
0xD0: "Taito",
0xD1: "SOFEL (Software Engineering Lab)",
0xD2: "Quest",
0xD3: "Sigma Enterprises",
0xD4: "ASK Kodansha Co.",
0xD6: "Naxat Soft14",
0xD7: "Copya System",
0xD9: "Banpresto",
0xDA: "Tomy",
0xDB: "LJN",
0xDD: "Nippon Computer Systems",
0xDE: "Human Ent.",
0xDF: "Altron",
0xE0: "Jaleco",
0xE1: "Towa Chiki",
0xE2: "Yutaka # Needs more info",
0xE3: "Varie",
0xE5: "Epoch",
0xE7: "Athena",
0xE8: "Asmik Ace Entertainment",
0xE9: "Natsume",
0xEA: "King Records",
0xEB: "Atlus",
0xEC: "Epic/Sony Records",
0xEE: "IGS",
0xF0: "A Wave",
0xF3: "Extreme Entertainment",
0xFF: "LJN",
}
type ROMHeader struct {
EntryPoint [4]byte
Logo [48]byte
// NOTE(m): Assuming "old" cartridges here. This may cause problems with newer cartridges.
// See https://gbdev.io/pandocs/The_Cartridge_Header.html#0134-0143--title
Title [16]byte
NewLicenseeCode [2]byte
SGBFlag byte
CartridgeType byte
ROMSize byte
RAMSize byte
DestinationCode byte
OldLicenseeCode byte
MaskROMVersionNumber byte
HeaderChecksum byte
GlobalChecksum [2]byte
}
type Cartridge struct {
Filename string
Mapper string
Title string
Licensee string
SGBSupport bool
ROMSize int
RAMSize string
Destination string
Version int
}
func Insert(filename string) Cartridge {
file, err := os.Open(filename)
if err != nil {
log.Fatal(err)
}
defer file.Close()
cartridge := Cartridge{Filename: file.Name()}
// Jump to start of header
_, err = file.Seek(0x0100, io.SeekStart)
if err != nil {
log.Fatal(err)
}
// Read header
var header ROMHeader
err = binary.Read(file, binary.LittleEndian, &header)
if err != nil {
log.Fatal(err)
}
// Validate the ROM by checking presence of the Nintendo logo
if header.Logo != expectedLogo {
log.Fatal("Invalid ROM file: No valid logo found!")
}
// Convert some header values
cartridge.Title = string(bytes.Trim(header.Title[:], "\x00"))
cartridge.Mapper = cartridgeTypes[header.CartridgeType]
if header.OldLicenseeCode == 0x33 {
// FIXME(m): Support new licensee codes
cartridge.Licensee = "Indicates that the New licensee code should be used instead."
} else {
cartridge.Licensee = oldLicensees[header.OldLicenseeCode]
}
cartridge.SGBSupport = (header.SGBFlag == 0x03)
cartridge.ROMSize = 32 * (1 << header.ROMSize)
cartridge.RAMSize = ramSizes[header.RAMSize]
switch header.DestinationCode {
case 0x00:
cartridge.Destination = "Japan (and possibly overseas)"
case 0x01:
cartridge.Destination = "Overseas only"
default:
cartridge.Destination = "UNKNOWN"
}
cartridge.Version = int(header.MaskROMVersionNumber)
// TODO(m): Verify header checksum
// NOTE(m): Ignoring global checksum which is not used, except by one emulator.
// See https://gbdev.io/pandocs/The_Cartridge_Header.html#014e-014f--global-checksum
return cartridge
}

41
gb/cartridge.go
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@ -3,8 +3,7 @@ package gb
import (
"bytes"
"encoding/binary"
"io"
"log"
"fmt"
"os"
)
@ -215,6 +214,7 @@ var oldLicensees = map[byte]string{
}
type ROMHeader struct {
_ [256]byte
EntryPoint [4]byte
Logo [48]byte
// NOTE(m): Assuming "old" cartridges here. This may cause problems with newer cartridges.
@ -228,7 +228,7 @@ type ROMHeader struct {
DestinationCode byte
OldLicenseeCode byte
MaskROMVersionNumber byte
HeaderChecksum byte
Checksum byte
GlobalChecksum [2]byte
}
@ -242,32 +242,23 @@ type Cartridge struct {
RAMSize string
Destination string
Version int
Checksum byte
}
func InsertCartridge(path string) *Cartridge {
file, err := os.Open(path)
if err != nil {
log.Fatal(err)
}
defer file.Close()
cartridge := Cartridge{Filename: file.Name()}
func InsertCartridge(filename string) (*Cartridge, error) {
cartridge := Cartridge{Filename: filename}
// Jump to start of header
_, err = file.Seek(0x0100, io.SeekStart)
rom, err := os.ReadFile(filename)
if err != nil {
log.Fatal(err)
return &cartridge, err
}
// Read header
var header ROMHeader
err = binary.Read(file, binary.LittleEndian, &header)
buffer := bytes.NewReader(rom)
err = binary.Read(buffer, binary.LittleEndian, &header)
if err != nil {
log.Fatal(err)
}
// Validate the ROM by checking presence of the Nintendo logo
if header.Logo != expectedLogo {
log.Fatal("Invalid ROM file: No valid logo found!")
return &cartridge, nil
}
// Convert some header values
@ -292,10 +283,16 @@ func InsertCartridge(path string) *Cartridge {
}
cartridge.Version = int(header.MaskROMVersionNumber)
// TODO(m): Verify header checksum
// Calculate and verify checksum
for address := uint16(0x0134); address <= uint16(0x014C); address++ {
cartridge.Checksum = cartridge.Checksum - rom[address] - 1
}
if cartridge.Checksum != header.Checksum {
return &cartridge, fmt.Errorf("ROM checksum failed: %X does not equal %X", cartridge.Checksum, header.Checksum)
}
// NOTE(m): Ignoring global checksum which is not used, except by one emulator.
// See https://gbdev.io/pandocs/The_Cartridge_Header.html#014e-014f--global-checksum
return &cartridge
return &cartridge, nil
}

16
cartridge_test.go → gb/cartridge_test.go
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@ -1,4 +1,4 @@
package main
package gb
import (
"testing"
@ -6,10 +6,13 @@ import (
"github.com/stretchr/testify/assert"
)
func TestInsertCartridge(t *testing.T) {
cartridge := Insert("./roms/dmg-acid2.gb")
func TestInsert(t *testing.T) {
cartridge, err := InsertCartridge("../roms/dmg-acid2.gb")
assert := assert.New(t)
assert.Nil(err)
assert.Equal(cartridge.Filename, "../roms/dmg-acid2.gb")
assert.Equal(cartridge.Title, "DMG-ACID2")
assert.Equal(cartridge.Mapper, "ROM ONLY")
assert.Equal(cartridge.Licensee, "None")
@ -18,4 +21,11 @@ func TestInsertCartridge(t *testing.T) {
assert.Equal(cartridge.RAMSize, "0 - No RAM")
assert.Equal(cartridge.Destination, "Japan (and possibly overseas)")
assert.Equal(cartridge.Version, 0)
assert.Equal(cartridge.Checksum, byte(0x9F))
}
func TestFailedChecksum(t *testing.T) {
_, err := InsertCartridge("../roms/failed-checksum.gb")
assert.EqualError(t, err, "ROM checksum failed: 9F does not equal 41")
}

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roms/failed-checksum.gb Normal file
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