Skip to content

Commit

Permalink
MMC2 cart read/write support, rom refactor
Browse files Browse the repository at this point in the history
  • Loading branch information
@scottferg
scottferg committed Sep 16, 2013
1 parent e5f3773 commit c9bb8c2
Show file tree
Hide file tree
Showing 3 changed files with 113 additions and 83 deletions.
7 changes: 7 additions & 0 deletions nes/mmc1.go
View file
Original file line number Diff line number Diff line change
Expand Up @@ -3,6 +3,13 @@ package nes
const (
BankUpper = iota
BankLower

Size1k = 0x0400
Size2k = 0x0800
Size4k = 0x1000
Size8k = 0x2000
Size16k = 0x4000
Size32k = 0x8000
)

type Mmc1 struct {
Expand Down
137 changes: 102 additions & 35 deletions nes/mmc2.go
View file
Original file line number Diff line number Diff line change
@@ -1,5 +1,9 @@
package nes

import (
"fmt"
)

const (
RegisterPrgBankSelect = iota
RegisterChrBank1Select
Expand All @@ -24,6 +28,14 @@ type Mmc2 struct {
LatchFE1 int
LatchFD0 int
LatchFD1 int

PrgUpperHighBank int
PrgUpperLowBank int
PrgLowerHighBank int
PrgLowerLowBank int

ChrHighBank int
ChrLowBank int
}

func NewMmc2(r *Nrom) *Mmc2 {
Expand All @@ -43,32 +55,65 @@ func NewMmc2(r *Nrom) *Mmc2 {
m.LatchFD1 = 0
m.LatchFE1 = 0

m.LoadRom()
m.Load()

return m
}

func (m *Mmc2) LoadRom() {
func (m *Mmc2) Load() {
// 2x the banks since we're storing 8k per bank
// instead of 16k
fmt.Printf(" Emulated PRG banks: %d\n", 2*m.PrgBankCount)
m.RomBanks = make([][]Word, 2*m.PrgBankCount)
for i := 0; i < 2*m.PrgBankCount; i++ {
// Move 8kb chunk to 8kb bank
bank := make([]Word, 0x2000)
for x := 0; x < 0x2000; x++ {
bank[x] = Word(m.Data[(0x2000*i)+x])
}

m.RomBanks[i] = bank
}

// Everything after PRG-ROM
chrRom := m.Data[0x2000*len(m.RomBanks):]

// CHR is stored in 4k banks
m.VromBanks = make([][]Word, m.ChrRomCount*2)

for i := 0; i < cap(m.VromBanks); i++ {
// Move 16kb chunk to 16kb bank
m.VromBanks[i] = make([]Word, 0x1000)

// If the game doesn't have CHR banks we
// just need to allocate VRAM

for x := 0; x < 0x1000; x++ {
var val Word
if m.ChrRomCount == 0 {
val = 0
} else {
val = Word(chrRom[(0x1000*i)+x])
}
m.VromBanks[i][x] = val
}
}

// The PRG banks are 8192 bytes in size, half the size of an
// iNES PRG bank. If your emulator or copier handles PRG data
// in 16384 byte chunks, you can think of the lower bit as
// selecting the first or second half of the bank
//
// http://forums.nesdev.com/viewtopic.php?p=38182#p38182

// Write swappable PRG banks (0x8000 and 0xA000)
m.Write8kRamBank(0, 0x8000)

m.PrgLowerLowBank = 0
// Write hardwired PRG banks (0xC000 and 0xE000)
// Third to last bank
m.Write8kRamBank(((len(m.RomBanks)-2)*2)+1, 0xA000)
// Second to last bank
m.Write8kRamBank((len(m.RomBanks)-1)*2, 0xC000)
m.PrgUpperHighBank = (((len(m.RomBanks) - 1) * 2) + 1) % len(m.RomBanks)
m.PrgUpperLowBank = ((len(m.RomBanks) - 1) * 2) % len(m.RomBanks)
// Last bank
m.Write8kRamBank(((len(m.RomBanks)-1)*2)+1, 0xE000)

WriteVramBank(m.VromBanks, 4, 0x0000, Size4k)
WriteVramBank(m.VromBanks, 0, 0x1000, Size4k)
m.PrgLowerHighBank = (((len(m.RomBanks) - 2) * 2) + 1) % len(m.RomBanks)
}

func (m *Mmc2) Write(v Word, a int) {
Expand All @@ -88,20 +133,46 @@ func (m *Mmc2) Write(v Word, a int) {
}
}

func (m *Mmc2) Read(a int) Word {
return 0
}

func (m *Mmc2) WriteVram(v Word, a int) {
// Nothing to do
switch {
case a >= 0x1000:
m.VromBanks[m.ChrHighBank][a&0xFFF] = v
default:
m.VromBanks[m.ChrLowBank][a&0xFFF] = v
}
}

func (m *Mmc2) ReadVram(a int) Word {
return 0
switch {
case a >= 0x1000:
return m.VromBanks[m.ChrHighBank][a&0xFFF]
default:
return m.VromBanks[m.ChrLowBank][a&0xFFF]
}
}

func (m *Mmc2) ReadTile(a int) []Word {
return []Word{}
switch {
case a >= 0x1000:
return m.VromBanks[m.ChrHighBank][a&0xFFF : a&0xFFF+16]
default:
return m.VromBanks[m.ChrLowBank][a&0xFFF : a&0xFFF+16]
}
}

func (m *Mmc2) Read(a int) Word {
switch {
case a >= 0xE000:
return m.RomBanks[m.PrgUpperHighBank][a&0x1FFF]
case a >= 0xC000:
return m.RomBanks[m.PrgUpperLowBank][a&0x1FFF]
case a >= 0xA000:
return m.RomBanks[m.PrgLowerHighBank][a&0x1FFF]
case a >= 0x8000:
return m.RomBanks[m.PrgLowerLowBank][a&0x1FFF]
}

return 0
}

func (m *Mmc2) LatchTrigger(a int) {
Expand All @@ -110,16 +181,20 @@ func (m *Mmc2) LatchTrigger(a int) {
switch {
case a == 0x0FD0 && m.LatchLow != 0xFD:
m.LatchLow = 0xFD
WriteVramBank(m.VromBanks, m.LatchFD0%len(m.VromBanks), 0x0000, Size4k)

m.ChrLowBank = m.LatchFD0 % len(m.VromBanks)
case a == 0x0FE0 && m.LatchLow != 0xFE:
m.LatchLow = 0xFE
WriteVramBank(m.VromBanks, m.LatchFE0%len(m.VromBanks), 0x0000, Size4k)

m.ChrLowBank = m.LatchFE0 % len(m.VromBanks)
case a == 0x1FD0 && m.LatchHigh != 0xFD:
m.LatchHigh = 0xFD
WriteVramBank(m.VromBanks, m.LatchFD1%len(m.VromBanks), 0x1000, Size4k)

m.ChrHighBank = m.LatchFD1 % len(m.VromBanks)
case a == 0x1FE0 && m.LatchHigh != 0xFE:
m.LatchHigh = 0xFE
WriteVramBank(m.VromBanks, m.LatchFE1%len(m.VromBanks), 0x1000, Size4k)

m.ChrHighBank = m.LatchFE1 % len(m.VromBanks)
}
}

Expand Down Expand Up @@ -147,8 +222,7 @@ func (m *Mmc2) RegisterNumber(a int) int {
}

func (m *Mmc2) PrgBankSelect(v Word) {
bank := int(v & 0xF)
m.Write8kRamBank(bank, 0x8000)
m.PrgLowerLowBank = int(v&0xF) % len(m.RomBanks)
}

func (m *Mmc2) ChrBankSelect(v Word, b int) {
Expand All @@ -159,25 +233,25 @@ func (m *Mmc2) ChrBankSelect(v Word, b int) {
m.LatchFD0 = int(v)

if m.LatchLow == 0xFD {
WriteVramBank(m.VromBanks, m.LatchFD0%len(m.VromBanks), 0x0000, Size4k)
m.ChrLowBank = m.LatchFD0 % len(m.VromBanks)
}
case 2:
m.LatchFE0 = int(v)

if m.LatchLow == 0xFE {
WriteVramBank(m.VromBanks, m.LatchFE0%len(m.VromBanks), 0x0000, Size4k)
m.ChrLowBank = m.LatchFE0 % len(m.VromBanks)
}
case 3:
m.LatchFD1 = int(v)

if m.LatchHigh == 0xFD {
WriteVramBank(m.VromBanks, m.LatchFD1%len(m.VromBanks), 0x1000, Size4k)
m.ChrHighBank = m.LatchFD1 % len(m.VromBanks)
}
case 4:
m.LatchFE1 = int(v)

if m.LatchHigh == 0xFE {
WriteVramBank(m.VromBanks, m.LatchFE1%len(m.VromBanks), 0x1000, Size4k)
m.ChrHighBank = m.LatchFE1 % len(m.VromBanks)
}
}
}
Expand All @@ -189,10 +263,3 @@ func (m *Mmc2) MirroringSelect(v Word) {
ppu.Nametables.SetMirroring(MirroringVertical)
}
}

func (m *Mmc2) Write8kRamBank(bank, dest int) {
b := (bank >> 1) % len(m.RomBanks)
offset := (bank % 2) * 0x2000

WriteOffsetRamBank(m.RomBanks, b, dest, Size8k, offset)
}
52 changes: 4 additions & 48 deletions nes/rom.go
View file
Original file line number Diff line number Diff line change
Expand Up @@ -5,15 +5,6 @@ import (
"fmt"
)

const (
Size1k = 0x0400
Size2k = 0x0800
Size4k = 0x1000
Size8k = 0x2000
Size16k = 0x4000
Size32k = 0x8000
)

type Mapper interface {
Write(v Word, a int)
Read(a int) Word
Expand All @@ -23,39 +14,6 @@ type Mapper interface {
BatteryBacked() bool
}

func WriteRamBank(rom [][]Word, bank, dest, size int) {
bank %= len(rom)

for i := 0; i < size; i++ {
Ram[i+dest] = rom[bank][i]
}
}

// Used by MMC3 for selecting 8kb chunks of a PRG-ROM bank
func WriteOffsetRamBank(rom [][]Word, bank, dest, size, offset int) {
bank %= len(rom)

for i := 0; i < size; i++ {
Ram[i+dest] = rom[bank][i+offset]
}
}

func WriteVramBank(rom [][]Word, bank, dest, size int) {
bank %= len(rom)

for i := 0; i < size; i++ {
ppu.Vram[i+dest] = rom[bank][i]
}
}

func WriteOffsetVramBank(rom [][]Word, bank, dest, size, offset int) {
bank %= len(rom)

for i := 0; i < size; i++ {
ppu.Vram[i+dest] = rom[bank][i+offset]
}
}

func LoadRom(rom []byte) (m Mapper, e error) {
r := new(Nrom)

Expand Down Expand Up @@ -160,12 +118,10 @@ func LoadRom(rom []byte) (m Mapper, e error) {
// MMC5
fmt.Printf("MMC5\n")
m = NewMmc5(r)
/*
case 0x09:
// MMC2
fmt.Printf("MMC2\n")
m = NewMmc2(r)
*/
case 0x09:
// MMC2
fmt.Printf("MMC2\n")
m = NewMmc2(r)
default:
// Unsupported
fmt.Printf("Unsupported\n")
Expand Down

0 comments on commit c9bb8c2

Please sign in to comment.