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mbc3.go
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mbc3.go
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package memory
type mbc3 struct {
// ROM and RAM data and mask read from the cart
rom [][0x4000]byte
ram [][0x2000]byte
// Internal state
ramEnabled bool
romBank uint8
ramBank uint8
rtc *rtc
}
func newMBC3(rom [][0x4000]byte, ram [][0x2000]byte, rtc *rtc) mbc {
mbc := &mbc3{
rom: rom,
ram: ram,
romBank: 1,
rtc: rtc,
}
return mbc
}
func (m *mbc3) Read(addr uint16) uint8 {
switch {
case addr < 0x4000:
return m.rom[0][addr]
case addr < 0x8000:
offset := addr - 0x4000
return m.rom[m.romBank][offset]
case addr < 0xa000:
return 0xff
case addr < 0xc000:
if m.ramEnabled {
if m.ramBank >= 0x08 {
return m.rtc.read(m.ramBank)
}
offset := addr - 0xa000
return m.ram[m.ramBank][offset]
}
return 0xff
default:
return 0xff
}
}
func (m *mbc3) Write(addr uint16, value uint8) {
switch {
case addr < 0x2000:
m.ramEnabled = value&0x0f == 0x0a
case addr < 0x4000:
m.romBank = value & 0x7f
case addr < 0x6000:
m.ramBank = value & 0x0f
case addr < 0x8000:
if value&0x01 == 0 {
m.rtc.latchLow()
} else {
m.rtc.latchHigh()
}
case addr < 0xa000:
// Ignore
case addr < 0xc000:
offset := addr - 0xa000
if m.ramEnabled {
if m.ramBank >= 0x08 {
m.rtc.write(m.ramBank, value)
return
}
m.ram[m.ramBank][offset] = value
}
default:
// Ignore
}
}
func (m *mbc3) DumpRAM() []byte {
var dump []byte
for _, r := range m.ram {
dump = append(dump, r[:]...)
}
return dump
}