Add echo RAM and umapped RAM region handlers

maxfierke · Jan 7, 2024 · 3477c07 · 3477c07
1 parent 0c05705
commit 3477c07
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Showing 2 changed files with 37 additions and 3 deletions.
diff --git a/hardware/dmg.go b/hardware/dmg.go
@@ -45,17 +45,22 @@ func NewDMGDebug(debugger debug.Debugger) (*DMG, error) {
 
 	ram := make([]byte, DMG_RAM_SIZE)
 	mmu := mem.NewMMU(ram)
+	echo := mem.NewEchoRegion()
+	unmapped := mem.NewUnmappedRegion()
 
 	mmu.AddHandler(mem.MemRegion{Start: 0x0000, End: 0xFFFF}, debugger)
 
 	mmu.AddHandler(mem.MemRegion{Start: 0x0000, End: 0x7FFF}, cartridge) // MBCs ROM Banks
 	mmu.AddHandler(mem.MemRegion{Start: 0xA000, End: 0xBFFF}, cartridge) // MBCs RAM Banks
 
-	mmu.AddHandler(mem.MemRegion{Start: 0xFF40, End: 0xFF4B}, lcd) // LCD control registers
+	mmu.AddHandler(mem.MemRegion{Start: 0xE000, End: 0xFDFF}, echo)     // Echo RAM (mirrors WRAM)
+	mmu.AddHandler(mem.MemRegion{Start: 0xFEA0, End: 0xFEFF}, unmapped) // Nop writes, zero reads
+
+	mmu.AddHandler(mem.MemRegion{Start: 0xFF01, End: 0xFF02}, serial) // Serial Port (Control & Data)
+	mmu.AddHandler(mem.MemRegion{Start: 0xFF40, End: 0xFF4B}, lcd)    // LCD control registers
 
-	mmu.AddHandler(mem.MemRegion{Start: 0xFFFF, End: 0xFFFF}, ic)
 	mmu.AddHandler(mem.MemRegion{Start: 0xFF0F, End: 0xFF0F}, ic)
-	mmu.AddHandler(mem.MemRegion{Start: 0xFF01, End: 0xFF02}, serial)
+	mmu.AddHandler(mem.MemRegion{Start: 0xFFFF, End: 0xFFFF}, ic)
 
 	return &DMG{
 		cpu:       cpu,

diff --git a/mem/mmu.go b/mem/mmu.go
@@ -78,6 +78,35 @@ type MemBus interface {
 	Write16(addr uint16, value uint16)
 }
 
+type EchoRegion struct{}
+
+func NewEchoRegion() *EchoRegion {
+	return &EchoRegion{}
+}
+
+func (umr *EchoRegion) OnRead(mmu *MMU, addr uint16) MemRead {
+	// Echo mirrors 0xC000
+	return ReadReplace(mmu.ram[addr-0x2000])
+}
+
+func (umr *EchoRegion) OnWrite(mmu *MMU, addr uint16, value byte) MemWrite {
+	return WriteBlock()
+}
+
+type UnmappedRegion struct{}
+
+func NewUnmappedRegion() *UnmappedRegion {
+	return &UnmappedRegion{}
+}
+
+func (umr *UnmappedRegion) OnRead(mmu *MMU, addr uint16) MemRead {
+	return ReadReplace(0x00)
+}
+
+func (umr *UnmappedRegion) OnWrite(mmu *MMU, addr uint16, value byte) MemWrite {
+	return WriteBlock()
+}
+
 func NewMMU(ram []byte) *MMU {
 	return &MMU{
 		ram:           ram,