memory - Add way to map register into address space

Makeconf

@@ -2,6 +2,7 @@ modules := memory/mem_device \
            memory/bus \
            memory/ram \
            memory/bootrom_overlay \
+           memory/register \
            cpu/cpu \
            cpu/decoder
 

memory/register.cpp

@@ -0,0 +1,13 @@
+#include <memory/register.h>
+
+void BoundRegister::write8(u16 addr, u8 data)
+{
+  if(addr) return;
+  reg = data;
+}
+
+u8 BoundRegister::read8(u16 addr)
+{
+  if(addr) return 0xFF;
+  return reg;
+}

memory/register.h

@@ -0,0 +1,17 @@
+#pragma once
+
+#include <misc/types.h>
+#include <memory/mem_device.h>
+
+class BoundRegister : public Mem_device {
+private:
+  u8& reg;
+public:
+  inline
+  BoundRegister(u8& reg)
+    : reg(reg)
+  {}
+
+  virtual void write8(u16 addr, u8 data);
+  virtual u8 read8(u16 addr);
+};