1 files changed, 47 insertions, 0 deletions
diff --git a/cart/nrom.go b/cart/nrom.go
new file mode 100644
index 0000000..3828c16
--- /dev/null
+++ b/cart/nrom.go
@@ -0,0 +1,47 @@
+package cart
+
+type nrom struct {
+	prg       []uint8
+	chr       []uint8
+	chrIsRAM  bool
+	prgRAM    [8 * 1024]uint8
+	mirroring Mirroring
+}
+
+func newNROM(c *Cartridge) *nrom {
+	return &nrom{
+		prg:       c.PRG,
+		chr:       c.CHR,
+		chrIsRAM:  c.CHRIsRAM,
+		mirroring: c.Mirroring,
+	}
+}
+
+func (m *nrom) CPURead(addr uint16) uint8 {
+	switch {
+	case addr >= 0x8000:
+		return m.prg[int(addr-0x8000)%len(m.prg)]
+	case addr >= 0x6000:
+		return m.prgRAM[addr-0x6000]
+	default:
+		return 0
+	}
+}
+
+func (m *nrom) CPUWrite(addr uint16, v uint8) {
+	if addr >= 0x6000 && addr < 0x8000 {
+		m.prgRAM[addr-0x6000] = v
+	}
+}
+
+func (m *nrom) PPURead(addr uint16) uint8 {
+	return m.chr[int(addr)%len(m.chr)]
+}
+
+func (m *nrom) PPUWrite(addr uint16, v uint8) {
+	if m.chrIsRAM {
+		m.chr[int(addr)%len(m.chr)] = v
+	}
+}
+
+func (m *nrom) Mirroring() Mirroring { return m.mirroring }