/
mapper002.go
105 lines (87 loc) · 2.04 KB
/
mapper002.go
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package ines
import (
"errors"
"log"
"github.com/maxpoletaev/dendy/internal/binario"
)
type Mapper2 struct {
rom *ROM
prgBank0 int
prgBank1 int
}
func NewMapper2(rom *ROM) *Mapper2 {
return &Mapper2{
rom: rom,
}
}
func (m *Mapper2) Reset() {
m.prgBank0 = 0
m.prgBank1 = m.rom.PRGBanks - 1
}
func (m *Mapper2) ScanlineTick() {
}
func (m *Mapper2) PendingIRQ() bool {
return false
}
func (m *Mapper2) MirrorMode() MirrorMode {
return m.rom.MirrorMode
}
func (m *Mapper2) ReadPRG(addr uint16) byte {
switch {
case addr >= 0x8000 && addr <= 0xBFFF:
// Read from the first 16KB PRG-ROM bank (fixed).
idx := m.prgBank0*0x4000 + int(addr-0x8000)
idx %= len(m.rom.PRG)
return m.rom.PRG[idx]
case addr >= 0xC000 && addr <= 0xFFFF:
// Read from the last 16KB PRG-ROM bank (switchable).
idx := m.prgBank1*0x4000 + int(addr-0xC000)
idx %= len(m.rom.PRG)
return m.rom.PRG[idx]
default:
log.Printf("[WARN] mapper2: unhandled prg read at 0x%04X", addr)
return 0
}
}
func (m *Mapper2) WritePRG(addr uint16, data byte) {
// The lower 4 bits of the data written to 0x8000-0xFFFF select the
// 16KB PRG-ROM bank at 0xC000-0xFFFF. The upper 4 bits are ignored.
m.prgBank0 = int(data & 0x0F)
}
func (m *Mapper2) ReadCHR(addr uint16) byte {
switch {
case addr >= 0x0000 && addr <= 0x1FFF:
return m.rom.CHR[addr]
default:
log.Printf("[WARN] mapper2: unhandled chr read at 0x%04X", addr)
return 0
}
}
func (m *Mapper2) WriteCHR(addr uint16, data byte) {
if !m.rom.chrRAM {
log.Printf("[WARN] mapper2: write to read-only chr at %04X", addr)
return
}
m.rom.CHR[addr] = data
}
func (m *Mapper2) SaveState(w *binario.Writer) error {
return errors.Join(
m.rom.SaveState(w),
w.WriteUint64(uint64(m.prgBank0)),
w.WriteUint64(uint64(m.prgBank1)),
)
}
func (m *Mapper2) LoadState(w *binario.Reader) error {
var (
prgBank0 uint64
prgBank1 uint64
)
err := errors.Join(
m.rom.LoadState(w),
w.ReadUint64To(&prgBank0),
w.ReadUint64To(&prgBank1),
)
m.prgBank0 = int(prgBank0)
m.prgBank1 = int(prgBank1)
return err
}