memory/mbc - Partial implementation of MBC1

Makeconf

@@ -4,6 +4,7 @@ modules := memory/device \
            memory/bootrom_overlay \
            memory/register \
 		   memory/bank \
+           memory/mbc/mbc1 \
            cpu/cpu \
            cpu/decoder \
            cartridge/cartridge

memory/mbc/mbc1.cpp

@@ -0,0 +1,39 @@
+#include <memory/mbc/mbc1.h>
+#include <misc/panic.h>
+
+MBC1::MBC1(Cartridge& cart)
+  : cart(cart),
+    main_bankreg(0),
+    external_ram(0x8000)
+{}
+
+u8 MBC1::read8(u16 addr)
+{
+  if((addr & 0xC000) == 0x0000)
+    return cart[addr];
+  else if((addr & 0xC000) == 0x4000)
+    {
+      u8 bank = main_bankreg ? main_bankreg : 1;
+      u8 numbanks = cart.size() >> 14;
+      return cart[(bank % numbanks) << 14 | (addr - 0x4000)];
+    }
+  else if((addr & 0xE000) == 0xA000)
+    {
+      if(!ram_enabled) return 0xFF;
+      return external_ram.read8(ram_bankreg << 13 | (addr - 0xA000));
+    }
+  else
+    return 0xFF;
+}
+
+void MBC1::write8(u16 addr, u8 data)
+{
+  if((addr & 0xE000) == 0x0000)
+    ram_enabled = ((data & 0x0F) == 0x0A);
+  else if((addr & 0xE000) == 0x2000)
+    main_bankreg = data & 0x1F;
+  else if((addr & 0xE000) == 0x4000)
+    ram_bankreg = data & 0x03;
+  else if((addr & 0xE000) == 0x6000)
+    panic("Banking mode not implemented");
+}

memory/mbc/mbc1.h

@@ -0,0 +1,22 @@
+#pragma once
+
+#include <memory/device.h>
+#include <memory/ram.h>
+#include <cartridge/cartridge.h>
+
+class MBC1 : public Mem_device {
+private:
+  Cartridge& cart;
+  u8 main_bankreg;
+  u8 ram_bankreg;
+
+  bool ram_enabled;
+
+  RAM external_ram;
+
+public:
+  MBC1(Cartridge& cart);
+
+  virtual void write8(u16 addr, u8 data);
+  virtual u8 read8(u16 addr);
+};