diff --git a/gameboy/cartridge/cartridge.cpp b/gameboy/cartridge/cartridge.cpp
index f7e47556..aaf2c30d 100755
--- a/gameboy/cartridge/cartridge.cpp
+++ b/gameboy/cartridge/cartridge.cpp
@@ -6,6 +6,7 @@ namespace GameBoy {
 #include "mbc0/mbc0.cpp"
 #include "mbc1/mbc1.cpp"
 #include "mbc2/mbc2.cpp"
+#include "mbc3/mbc3.cpp"
 #include "mbc5/mbc5.cpp"
 Cartridge cartridge;
 
@@ -34,6 +35,13 @@ void Cartridge::load(uint8_t *data, unsigned size) {
     case 0x03: info.mapper = Mapper::MBC1; info.ram = true; info.battery = true; break;
     case 0x05: info.mapper = Mapper::MBC2; info.ram = true; break;
     case 0x06: info.mapper = Mapper::MBC2; info.ram = true; info.battery = true; break;
+    case 0x08: info.mapper = Mapper::MBC0; info.ram = true; break;
+    case 0x09: info.mapper = Mapper::MBC0; info.ram = true; info.battery = true; break;
+    case 0x0f: info.mapper = Mapper::MBC3; info.rtc = true; info.battery = true; break;
+    case 0x10: info.mapper = Mapper::MBC3; info.rtc = true; info.ram = true; info.battery = true; break;
+    case 0x11: info.mapper = Mapper::MBC3; break;
+    case 0x12: info.mapper = Mapper::MBC3; info.ram = true; break;
+    case 0x13: info.mapper = Mapper::MBC3; info.ram = true; info.battery = true; break;
     case 0x19: info.mapper = Mapper::MBC5; break;
     case 0x1a: info.mapper = Mapper::MBC5; info.ram = true; break;
     case 0x1b: info.mapper = Mapper::MBC5; info.ram = true; info.battery = true; break;
@@ -64,7 +72,7 @@ void Cartridge::load(uint8_t *data, unsigned size) {
     case 0x03: info.ramsize = 32 * 1024; break;
   }
 
-  if(info.mapper == Mapper::MBC2) info.ramsize = 256;  //512 x 4-bit
+  if(info.mapper == Mapper::MBC2) info.ramsize = 512;  //512 x 4-bit
 
   ramdata = new uint8_t[ramsize = info.ramsize]();
 
@@ -105,6 +113,7 @@ void Cartridge::power() {
   mbc0.power();
   mbc1.power();
   mbc2.power();
+  mbc3.power();
   mbc5.power();
 
   MMIO *mapper = 0;
@@ -112,6 +121,7 @@ void Cartridge::power() {
     case Mapper::MBC0: mapper = &mbc0; break;
     case Mapper::MBC1: mapper = &mbc1; break;
     case Mapper::MBC2: mapper = &mbc2; break;
+    case Mapper::MBC3: mapper = &mbc3; break;
     case Mapper::MBC5: mapper = &mbc5; break;
   }
 
diff --git a/gameboy/cartridge/cartridge.hpp b/gameboy/cartridge/cartridge.hpp
index 05eb052b..b04d16a0 100755
--- a/gameboy/cartridge/cartridge.hpp
+++ b/gameboy/cartridge/cartridge.hpp
@@ -2,12 +2,14 @@ struct Cartridge : property<Cartridge> {
   #include "mbc0/mbc0.hpp"
   #include "mbc1/mbc1.hpp"
   #include "mbc2/mbc2.hpp"
+  #include "mbc3/mbc3.hpp"
   #include "mbc5/mbc5.hpp"
 
   enum Mapper : unsigned {
     MBC0,
     MBC1,
     MBC2,
+    MBC3,
     MBC5,
     Unknown,
   };
diff --git a/gameboy/cartridge/mbc0/mbc0.cpp b/gameboy/cartridge/mbc0/mbc0.cpp
index fa9d616d..46461b77 100755
--- a/gameboy/cartridge/mbc0/mbc0.cpp
+++ b/gameboy/cartridge/mbc0/mbc0.cpp
@@ -1,11 +1,22 @@
 #ifdef CARTRIDGE_CPP
 
 uint8 Cartridge::MBC0::mmio_read(uint16 addr) {
-  if(addr >= 0x0000 && addr <= 0x7fff) return cartridge.rom_read(addr);
+  if((addr & 0x8000) == 0x0000) {  //0000-7fff
+    return cartridge.rom_read(addr);
+  }
+
+  if((addr & 0xe000) == 0xa000) {  //a000-bfff
+    return cartridge.ram_read(addr & 0x1fff);
+  }
+
   return 0x00;
 }
 
 void Cartridge::MBC0::mmio_write(uint16 addr, uint8 data) {
+  if((addr & 0xe000) == 0xa000) {  //a000-bfff
+    cartridge.ram_write(addr & 0x1fff, data);
+    return;
+  }
 }
 
 void Cartridge::MBC0::power() {
diff --git a/gameboy/cartridge/mbc1/mbc1.cpp b/gameboy/cartridge/mbc1/mbc1.cpp
index e31997dc..50622e82 100755
--- a/gameboy/cartridge/mbc1/mbc1.cpp
+++ b/gameboy/cartridge/mbc1/mbc1.cpp
@@ -1,48 +1,62 @@
 #ifdef CARTRIDGE_CPP
 
 uint8 Cartridge::MBC1::mmio_read(uint16 addr) {
-  if(addr >= 0x0000 && addr <= 0x3fff) {
+  if((addr & 0xc000) == 0x0000) {  //0000-3fff
     return cartridge.rom_read(addr);
   }
 
-  if(addr >= 0x4000 && addr <= 0x7fff) {
-    return cartridge.rom_read(rom_bank | (addr & 0x3fff));
+  if((addr & 0xc000) == 0x4000) {  //4000-7fff
+    if(mode_select == 0) {
+      return cartridge.rom_read((ram_select << 19) | (rom_select << 14) | (addr & 0x3fff));
+    } else {
+      return cartridge.rom_read((rom_select << 14) | (addr & 0x3fff));
+    }
   }
 
-  if(addr >= 0xa000 && addr <= 0xbfff) {
-    if(ram_enable) return cartridge.ram_read(ram_bank | (addr & 0x1fff));
+  if((addr & 0xe000) == 0xa000) {  //a000-bfff
+    if(ram_enable) {
+      if(mode_select == 0) {
+        return cartridge.ram_read(addr & 0x1fff);
+      } else {
+        return cartridge.ram_read((ram_select << 13) | (addr & 0x1fff));
+      }
+    }
     return 0x00;
   }
+
+  return 0x00;
 }
 
 void Cartridge::MBC1::mmio_write(uint16 addr, uint8 data) {
-  if(addr >= 0x0000 && addr <= 0x1fff) {
+  if((addr & 0xe000) == 0x0000) {  //0000-1fff
     ram_enable = (data & 0x0f) == 0x0a;
+    return;
   }
 
-  if(addr >= 0x2000 && addr <= 0x3fff) {
-    rom_select = data & 0x1f;
-    if(rom_select == 0) rom_select = 1;
+  if((addr & 0xe000) == 0x2000) {  //2000-3fff
+    rom_select = (data & 0x1f) + ((data & 0x1f) == 0);
+    return;
   }
 
-  if(addr >= 0x4000 && addr <= 0x5fff) {
+  if((addr & 0xe000) == 0x4000) {  //4000-5fff
     ram_select = data & 0x03;
+    return;
   }
 
-  if(addr >= 0x6000 && addr <= 0x7fff) {
+  if((addr & 0xe000) == 0x6000) {  //6000-7fff
     mode_select = data & 0x01;
+    return;
   }
 
-  if(mode_select == 0) {
-    rom_bank = (ram_select << 19) | (rom_select << 14);
-    ram_bank = 0x00;
-  } else {
-    rom_bank = (rom_select << 14);
-    ram_bank = (ram_select << 13);
-  }
-
-  if(addr >= 0xa000 && addr <= 0xbfff) {
-    if(ram_enable) cartridge.ram_write(ram_bank | (addr & 0x1fff), data);
+  if((addr & 0xe000) == 0xa000) {  //a000-bfff
+    if(ram_enable) {
+      if(mode_select == 0) {
+        cartridge.ram_write(addr & 0x1fff, data);
+      } else {
+        cartridge.ram_write((ram_select << 13) | (addr & 0x1fff), data);
+      }
+    }
+    return;
   }
 }
 
@@ -51,9 +65,6 @@ void Cartridge::MBC1::power() {
   rom_select = 0x01;
   ram_select = 0x00;
   mode_select = 0;
-
-  rom_bank = 0x4000;
-  ram_bank = 0x0000;
 }
 
 #endif
diff --git a/gameboy/cartridge/mbc1/mbc1.hpp b/gameboy/cartridge/mbc1/mbc1.hpp
index ccbb1bf3..099cf43d 100755
--- a/gameboy/cartridge/mbc1/mbc1.hpp
+++ b/gameboy/cartridge/mbc1/mbc1.hpp
@@ -4,9 +4,6 @@ struct MBC1 : MMIO {
   uint8 ram_select;   //4000-5fff
   bool  mode_select;  //6000-7fff
 
-  unsigned rom_bank;
-  unsigned ram_bank;
-
   uint8 mmio_read(uint16 addr);
   void mmio_write(uint16 addr, uint8 data);
   void power();
diff --git a/gameboy/cartridge/mbc2/mbc2.cpp b/gameboy/cartridge/mbc2/mbc2.cpp
index 491b21d6..3b952c78 100755
--- a/gameboy/cartridge/mbc2/mbc2.cpp
+++ b/gameboy/cartridge/mbc2/mbc2.cpp
@@ -1,19 +1,16 @@
 #ifdef CARTRIDGE_CPP
 
 uint8 Cartridge::MBC2::mmio_read(uint16 addr) {
-  if(addr >= 0x0000 && addr <= 0x3fff) {
+  if((addr & 0xc000) == 0x0000) {  //0000-3fff
     return cartridge.rom_read(addr);
   }
 
-  if(addr >= 0x4000 && addr <= 0x7fff) {
+  if((addr & 0xc000) == 0x4000) {  //4000-7fff
     return cartridge.rom_read((rom_select << 14) | (addr & 0x3fff));
   }
 
-  if(addr >= 0xa000 && addr <= 0xa1ff) {
-    if(ram_enable) {
-      uint8 data = cartridge.ram_read(addr & 0x1ff);
-      return (addr & 1) == 0 ? ((data >> 4) & 0x0f) : ((data >> 0) & 0x0f);
-    }
+  if((addr & 0xfe00) == 0xa000) {  //a000-a1ff
+    if(ram_enable) return cartridge.ram_read(addr & 0x1ff);
     return 0x00;
   }
 
@@ -21,29 +18,19 @@ uint8 Cartridge::MBC2::mmio_read(uint16 addr) {
 }
 
 void Cartridge::MBC2::mmio_write(uint16 addr, uint8 data) {
-  if(addr >= 0x0000 && addr <= 0x1fff) {
-    if((addr & 0x100) == 0) {
-      ram_enable = (data & 0x0f) == 0x0a;
-    }
+  if((addr & 0xe100) == 0x0000) {  //0000-1fff [d8=0]
+    ram_enable = (data & 0x0f) == 0x0a;
+    return;
   }
 
-  if(addr >= 0x2000 && addr <= 0x3fff) {
-    if(addr & 0x100) {
-      rom_select = data & 0x0f;
-      if(rom_select == 0) rom_select = 1;
-    }
+  if((addr & 0xe100) == 0x2100) {  //2000-3fff [d8=1]
+    rom_select = (data & 0x0f) + ((data & 0x0f) == 0);
+    return;
   }
 
-  if(addr >= 0xa000 && addr <= 0xa1ff) {
-    if(ram_enable) {
-      addr &= 511;
-      if((addr & 1) == 0) {
-        cartridge.ram_write(addr, (cartridge.ram_read(addr) & 0x0f) | (data << 4));
-      } else {
-        cartridge.ram_write(addr, (cartridge.ram_read(addr) & 0xf0) | (data << 0));
-      }
-      return;
-    }
+  if((addr & 0xfe00) == 0xa000) {  //a000-a1ff
+    if(ram_enable) cartridge.ram_write(addr & 0x1ff, data & 0x0f);
+    return;
   }
 }
 
diff --git a/gameboy/cartridge/mbc3/mbc3.cpp b/gameboy/cartridge/mbc3/mbc3.cpp
new file mode 100755
index 00000000..709970dc
--- /dev/null
+++ b/gameboy/cartridge/mbc3/mbc3.cpp
@@ -0,0 +1,120 @@
+#ifdef CARTRIDGE_CPP
+
+void Cartridge::MBC3::second() {
+  if(rtc_halt == false) {
+    if(++rtc_second >= 60) {
+      rtc_second = 0;
+      if(++rtc_minute >= 60) {
+        rtc_minute = 0;
+        if(++rtc_hour >= 24) {
+          rtc_hour = 0;
+          if(++rtc_day >= 512) {
+            rtc_day = 0;
+            rtc_day_carry = true;
+          }
+        }
+      }
+    }
+  }
+}
+
+uint8 Cartridge::MBC3::mmio_read(uint16 addr) {
+  if((addr & 0xc000) == 0x0000) {  //0000-3fff
+    return cartridge.rom_read(addr);
+  }
+
+  if((addr & 0xc000) == 0x4000) {  //4000-7fff
+    return cartridge.rom_read((rom_select << 13) | (addr & 0x3fff));
+  }
+
+  if((addr & 0xe000) == 0xa000) {  //a000-bfff
+    if(ram_enable) {
+      if(ram_select >= 0x00 && ram_select <= 0x03) {
+        return cartridge.ram_read((ram_select << 13) | (addr & 0x1fff));
+      }
+      if(ram_select == 0x08) return rtc_latch_second;
+      if(ram_select == 0x09) return rtc_latch_minute;
+      if(ram_select == 0x0a) return rtc_latch_hour;
+      if(ram_select == 0x0b) return rtc_latch_day;
+      if(ram_select == 0x0c) return (rtc_latch_day_carry << 7) | (rtc_latch_day >> 8);
+    }
+    return 0x00;
+  }
+
+  return 0x00;
+}
+
+void Cartridge::MBC3::mmio_write(uint16 addr, uint8 data) {
+  if((addr & 0xe000) == 0x0000) {  //0000-1fff
+    ram_enable = (data & 0x0f) == 0x0a;
+    return;
+  }
+
+  if((addr & 0xe000) == 0x2000) {  //2000-3fff
+    rom_select = (data & 0x7f) + ((data & 0x7f) == 0);
+    return;
+  }
+
+  if((addr & 0xe000) == 0x4000) {  //4000-5fff
+    ram_select = data;
+    return;
+  }
+
+  if((addr & 0xe000) == 0x6000) {  //6000-7fff
+    if(rtc_latch == 0 && data == 1) {
+      rtc_latch_second = rtc_second;
+      rtc_latch_minute = rtc_minute;
+      rtc_latch_hour = rtc_hour;
+      rtc_latch_day = rtc_day;
+      rtc_latch_day_carry = rtc_day_carry;
+    }
+    rtc_latch = data;
+    return;
+  }
+
+  if((addr & 0xe000) == 0xa000) {  //a000-bfff
+    if(ram_enable) {
+      if(ram_select >= 0x00 && ram_select <= 0x03) {
+        cartridge.ram_write((ram_select << 13) | (addr & 0x1fff), data);
+      } else if(ram_select == 0x08) {
+        if(data >= 60) data = 0;
+        rtc_second = data;
+      } else if(ram_select == 0x09) {
+        if(data >= 60) data = 0;
+        rtc_minute = data;
+      } else if(ram_select == 0x0a) {
+        if(data >= 24) data = 0;
+        rtc_hour = data;
+      } else if(ram_select == 0x0b) {
+        rtc_day = (rtc_day & 0x0100) | data;
+      } else if(ram_select == 0x0c) {
+        rtc_day = ((data & 1) << 8) | (rtc_day & 0xff);
+        rtc_halt = data & 0x40;
+        rtc_day_carry = data & 0x80;
+      }
+    }
+    return;
+  }
+}
+
+void Cartridge::MBC3::power() {
+  ram_enable = false;
+  rom_select = 0x01;
+  ram_select = 0x00;
+  rtc_latch = 0;
+
+  rtc_halt = true;
+  rtc_second = 0;
+  rtc_minute = 0;
+  rtc_hour = 0;
+  rtc_day = 0;
+  rtc_day_carry = false;
+
+  rtc_latch_second = 0;
+  rtc_latch_minute = 0;
+  rtc_latch_hour = 0;
+  rtc_latch_day = 0;
+  rtc_latch_day_carry = false;
+}
+
+#endif
diff --git a/gameboy/cartridge/mbc3/mbc3.hpp b/gameboy/cartridge/mbc3/mbc3.hpp
new file mode 100755
index 00000000..d83ba182
--- /dev/null
+++ b/gameboy/cartridge/mbc3/mbc3.hpp
@@ -0,0 +1,24 @@
+struct MBC3 : MMIO {
+  bool  ram_enable;  //0000-1fff
+  uint8 rom_select;  //2000-3fff
+  uint8 ram_select;  //4000-5fff
+  bool rtc_latch;    //6000-7fff
+
+  bool rtc_halt;
+  unsigned rtc_second;
+  unsigned rtc_minute;
+  unsigned rtc_hour;
+  unsigned rtc_day;
+  bool rtc_day_carry;
+
+  unsigned rtc_latch_second;
+  unsigned rtc_latch_minute;
+  unsigned rtc_latch_hour;
+  unsigned rtc_latch_day;
+  unsigned rtc_latch_day_carry;
+
+  void second();
+  uint8 mmio_read(uint16 addr);
+  void mmio_write(uint16 addr, uint8 data);
+  void power();
+} mbc3;
diff --git a/gameboy/cartridge/mbc5/mbc5.cpp b/gameboy/cartridge/mbc5/mbc5.cpp
index 0d209edf..263e5125 100755
--- a/gameboy/cartridge/mbc5/mbc5.cpp
+++ b/gameboy/cartridge/mbc5/mbc5.cpp
@@ -1,18 +1,16 @@
 #ifdef CARTRIDGE_CPP
 
 uint8 Cartridge::MBC5::mmio_read(uint16 addr) {
-  if(addr >= 0x0000 && addr <= 0x3fff) {
+  if((addr & 0xc000) == 0x0000) {  //0000-3fff
     return cartridge.rom_read(addr);
   }
 
-  if(addr >= 0x4000 && addr <= 0x7fff) {
+  if((addr & 0xc000) == 0x4000) {  //4000-7fff
     return cartridge.rom_read((rom_select << 14) | (addr & 0x3fff));
   }
 
-  if(addr >= 0xa000 && addr <= 0xbfff) {
-    if(ram_enable) {
-      return cartridge.ram_read((ram_select << 13) | (addr & 0x1fff));
-    }
+  if((addr & 0xe000) == 0xa000) {  //a000-bfff
+    if(ram_enable) return cartridge.ram_read((ram_select << 13) | (addr & 0x1fff));
     return 0x00;
   }
 
@@ -20,26 +18,29 @@ uint8 Cartridge::MBC5::mmio_read(uint16 addr) {
 }
 
 void Cartridge::MBC5::mmio_write(uint16 addr, uint8 data) {
-  if(addr >= 0x0000 && addr <= 0x1fff) {
+  if((addr & 0xe000) == 0x0000) {  //0000-1fff
     ram_enable = (data & 0x0f) == 0x0a;
+    return;
   }
 
-  if(addr >= 0x2000 && addr <= 0x2fff) {
+  if((addr & 0xf000) == 0x2000) {  //2000-2fff
     rom_select = (rom_select & 0x0100) | data;
+    return;
   }
 
-  if(addr >= 0x3000 && addr <= 0x3fff) {
+  if((addr & 0xf000) == 0x3000) {  //3000-3fff
     rom_select = ((data & 1) << 8) | (rom_select & 0x00ff);
+    return;
   }
 
-  if(addr >= 0x4000 && addr <= 0x5fff) {
+  if((addr & 0xe000) == 0x4000) {  //4000-5fff
     ram_select = data & 0x0f;
+    return;
   }
 
-  if(addr >= 0xa000 && addr <= 0xbfff) {
-    if(ram_enable) {
-      cartridge.ram_write((ram_select << 13) | (addr & 0x1fff), data);
-    }
+  if((addr & 0xe000) == 0xa000) {  //a000-bfff
+    if(ram_enable) cartridge.ram_write((ram_select << 13) | (addr & 0x1fff), data);
+    return;
   }
 }
 
diff --git a/gameboy/cpu/cpu.cpp b/gameboy/cpu/cpu.cpp
index e6739fc8..6978f965 100755
--- a/gameboy/cpu/cpu.cpp
+++ b/gameboy/cpu/cpu.cpp
@@ -14,7 +14,7 @@ void CPU::Main() {
 
 void CPU::main() {
   while(true) {
-  //print(disassemble(r[PC]), "\n");
+    if(trace) print(disassemble(r[PC]), "\n");
     interrupt_test();
     uint8 opcode = op_read(r[PC]++);
     (this->*opcode_table[opcode])();
@@ -27,7 +27,7 @@ void CPU::interrupt_raise(CPU::Interrupt id) {
     case Interrupt::Stat  : status.interrupt_request_stat   = 1; break;
     case Interrupt::Timer : status.interrupt_request_timer  = 1; break;
     case Interrupt::Serial: status.interrupt_request_serial = 1; break;
-    case Interrupt::Joypad: status.interrupt_request_joypad = 1; break;
+    case Interrupt::Joypad: status.interrupt_request_joypad = 1; status.stop = false; break;
   }
   status.halt = false;
 }
@@ -89,6 +89,7 @@ void CPU::power() {
   r[DE] = 0x0000;
   r[HL] = 0x0000;
 
+  status.clock = 0;
   status.halt = false;
   status.stop = false;
 
@@ -124,7 +125,7 @@ void CPU::power() {
   status.interrupt_enable_vblank = 0;
 }
 
-CPU::CPU() {
+CPU::CPU() : trace(false) {
   initialize_opcode_table();
 }
 
diff --git a/gameboy/cpu/cpu.hpp b/gameboy/cpu/cpu.hpp
index dc92a37c..23b632da 100755
--- a/gameboy/cpu/cpu.hpp
+++ b/gameboy/cpu/cpu.hpp
@@ -3,6 +3,8 @@ struct CPU : Processor, MMIO {
   #include "mmio/mmio.hpp"
   #include "timing/timing.hpp"
 
+  bool trace;
+
   enum class Interrupt : unsigned {
     Vblank,
     Stat,
@@ -12,6 +14,7 @@ struct CPU : Processor, MMIO {
   };
 
   struct Status {
+    unsigned clock;
     bool halt;
     bool stop;
 
diff --git a/gameboy/cpu/timing/timing.cpp b/gameboy/cpu/timing/timing.cpp
index b62c5995..987dc9ea 100755
--- a/gameboy/cpu/timing/timing.cpp
+++ b/gameboy/cpu/timing/timing.cpp
@@ -13,6 +13,12 @@
 #include "opcode.cpp"
 
 void CPU::add_clocks(unsigned clocks) {
+  status.clock += clocks;
+  if(status.clock >= 4 * 1024 * 1024) {
+    status.clock -= 4 * 1024 * 1024;
+    cartridge.mbc3.second();
+  }
+
   status.timer0 += clocks;
   if(status.timer0 >= 16) timer_stage0();
 
diff --git a/gameboy/gameboy.hpp b/gameboy/gameboy.hpp
index 777a7980..1a51634b 100755
--- a/gameboy/gameboy.hpp
+++ b/gameboy/gameboy.hpp
@@ -5,7 +5,7 @@
 namespace GameBoy {
   namespace Info {
     static const char Name[] = "bgameboy";
-    static const char Version[] = "000.07";
+    static const char Version[] = "000.08";
   }
 }
 
diff --git a/gameboy/lcd/lcd.cpp b/gameboy/lcd/lcd.cpp
index f29efea3..f555e40e 100755
--- a/gameboy/lcd/lcd.cpp
+++ b/gameboy/lcd/lcd.cpp
@@ -82,13 +82,11 @@ uint16 LCD::read_tile(bool select, unsigned x, unsigned y) {
 void LCD::render_bg() {
   unsigned iy = (status.ly + status.scy) & 255;
   unsigned ix = status.scx, tx = ix & 7;
-  uint8 mask = 0x80 >> tx;
-  unsigned data = read_tile(status.bg_tilemap_select, ix, iy), palette;
+  unsigned data = read_tile(status.bg_tilemap_select, ix, iy);
 
   for(unsigned ox = 0; ox < 160; ox++) {
-    palette  = ((data & (mask << 0)) ? 1 : 0);
-    palette |= ((data & (mask << 8)) ? 2 : 0);
-    mask = (mask >> 1) | (mask << 7);
+    uint8 palette = ((data & (0x0080 >> tx)) ? 1 : 0)
+                  | ((data & (0x8000 >> tx)) ? 2 : 0);
     line[ox] = status.bgp[palette];
 
     ix = (ix + 1) & 255;
@@ -102,13 +100,11 @@ void LCD::render_window() {
   if(status.ly - status.wy >= 144U) return;
   unsigned iy = status.ly - status.wy;
   unsigned ix = (status.wx - 7) & 255, tx = ix & 7;
-  uint8 mask = 0x80 >> tx;
-  unsigned data = read_tile(status.window_tilemap_select, ix, iy), palette;
+  unsigned data = read_tile(status.window_tilemap_select, ix, iy);
 
   for(unsigned ox = 0; ox < 160; ox++) {
-    palette  = ((data & (mask << 0)) ? 1 : 0);
-    palette |= ((data & (mask << 8)) ? 2 : 0);
-    mask = (mask >> 1) | (mask << 7);
+    uint8 palette = ((data & (0x0080 >> tx)) ? 1 : 0)
+                  | ((data & (0x8000 >> tx)) ? 2 : 0);
     if(ox - (status.wx - 7) < 160U) line[ox] = status.bgp[palette];
 
     ix = (ix + 1) & 255;
@@ -121,25 +117,53 @@ void LCD::render_window() {
 void LCD::render_obj() {
   unsigned obj_size = (status.obj_size == 0 ? 8 : 16);
 
+  unsigned sprite[10], sprites = 0;
+
+  //find first ten sprites on this scanline
   for(unsigned s = 0; s < 40; s++) {
     unsigned sy = oam[(s << 2) + 0] - 16;
     unsigned sx = oam[(s << 2) + 1] -  8;
-    unsigned tile = oam[(s << 2) + 2];
-    unsigned attribute = oam[(s << 2) + 3];
+
+    sy = status.ly - sy;
+    if(sy >= obj_size) continue;
+
+    sprite[sprites++] = s;
+    if(sprites == 10) break;
+  }
+
+  //sort by X-coordinate, when equal, lower address comes first
+  for(unsigned x = 0; x < sprites; x++) {
+    for(unsigned y = x + 1; y < sprites; y++) {
+      signed sx = oam[(sprite[x] << 2) + 1] - 8;
+      signed sy = oam[(sprite[y] << 2) + 1] - 8;
+      if(sy < sx) {
+        sprite[x] ^= sprite[y];
+        sprite[y] ^= sprite[x];
+        sprite[x] ^= sprite[y];
+      }
+    }
+  }
+
+  //render backwards, so that first sprite has highest priority
+  for(signed s = sprites - 1; s >= 0; s--) {
+    unsigned n = sprite[s] << 2;
+    unsigned sy = oam[n + 0] - 16;
+    unsigned sx = oam[n + 1] -  8;
+    unsigned tile = oam[n + 2];
+    unsigned attribute = oam[n + 3];
 
     sy = status.ly - sy;
     if(sy >= obj_size) continue;
     if(attribute & 0x40) sy ^= (obj_size - 1);
 
-    unsigned tdaddr = tile * 16 + sy * 2;
-
+    unsigned tdaddr = (tile << 4) + (sy << 1);
     uint8 d0 = vram[tdaddr + 0];
     uint8 d1 = vram[tdaddr + 1];
     unsigned xflip = attribute & 0x20 ? 7 : 0;
 
     for(unsigned tx = 0; tx < 8; tx++) {
-      uint8 palette = ((d0 & 0x80) >> 7) + ((d1 & 0x80) >> 6);
-      d0 <<= 1, d1 <<= 1;
+      uint8 palette = ((d0 & (0x80 >> tx)) ? 1 : 0)
+                    | ((d1 & (0x80 >> tx)) ? 2 : 0);
       if(palette == 0) continue;
 
       palette = status.obp[(bool)(attribute & 0x10)][palette];
diff --git a/ui/general/main-window.cpp b/ui/general/main-window.cpp
index 0fc97cf8..d20d9d11 100755
--- a/ui/general/main-window.cpp
+++ b/ui/general/main-window.cpp
@@ -15,7 +15,7 @@ void MainWindow::create() {
   settingsVideoSync.setChecked(true);
 
   tools.create(*this, "Tools");
-//tools.setEnabled(false);
+  toolsTraceCPU.create(tools, "Trace CPU");
 
   help.create(*this, "Help");
   helpAbout.create(help, "About ...");
@@ -43,6 +43,10 @@ void MainWindow::create() {
     video.set(Video::Synchronize, mainWindow.settingsVideoSync.checked());
   };
 
+  toolsTraceCPU.onTick = []() {
+    GameBoy::cpu.trace = mainWindow.toolsTraceCPU.checked();
+  };
+
   helpAbout.onTick = []() {
     MessageWindow::information(mainWindow, {
       "bgameboy\n\n",
diff --git a/ui/general/main-window.hpp b/ui/general/main-window.hpp
index f8ca8de5..57b8084f 100755
--- a/ui/general/main-window.hpp
+++ b/ui/general/main-window.hpp
@@ -8,6 +8,7 @@ struct MainWindow : Window {
   MenuCheckItem settingsVideoSync;
 
   Menu tools;
+  MenuCheckItem toolsTraceCPU;
 
   Menu help;
   MenuItem helpAbout;