diff --git a/src/bin/main.rs b/src/bin/main.rs
index c85a1f0..a1c193c 100644
--- a/src/bin/main.rs
+++ b/src/bin/main.rs
@@ -5,11 +5,11 @@ use clap::{App, ArgMatches};
 
 extern crate rustboyadvance_ng;
 
-use rustboyadvance_ng::arm7tdmi::Core;
-use rustboyadvance_ng::cartridge::Cartridge;
-use rustboyadvance_ng::debugger::Debugger;
+use rustboyadvance_ng::core::arm7tdmi::Core;
+use rustboyadvance_ng::core::cartridge::Cartridge;
+use rustboyadvance_ng::core::{GBAResult, GameBoyAdvance};
 use rustboyadvance_ng::util::read_bin_file;
-use rustboyadvance_ng::{GBAResult, GameBoyAdvance};
+use rustboyadvance_ng::debugger::Debugger;
 
 fn run_debug(matches: &ArgMatches) -> GBAResult<()> {
     let skip_bios = match matches.occurrences_of("skip_bios") {
diff --git a/src/arm7tdmi/alu.rs b/src/core/arm7tdmi/alu.rs
similarity index 100%
rename from src/arm7tdmi/alu.rs
rename to src/core/arm7tdmi/alu.rs
diff --git a/src/arm7tdmi/arm/display.rs b/src/core/arm7tdmi/arm/display.rs
similarity index 99%
rename from src/arm7tdmi/arm/display.rs
rename to src/core/arm7tdmi/arm/display.rs
index 371bb90..eb843f3 100644
--- a/src/arm7tdmi/arm/display.rs
+++ b/src/core/arm7tdmi/arm/display.rs
@@ -3,7 +3,7 @@ use std::fmt;
 use crate::bit::BitIndex;
 
 use super::{AluOpCode, ArmCond, ArmFormat, ArmHalfwordTransferType, ArmInstruction};
-use crate::arm7tdmi::{
+use crate::core::arm7tdmi::{
     psr::RegPSR, reg_string, Addr, BarrelShiftOpCode, BarrelShifterValue, ShiftedRegister, REG_PC,
 };
 
diff --git a/src/arm7tdmi/arm/exec.rs b/src/core/arm7tdmi/arm/exec.rs
similarity index 97%
rename from src/arm7tdmi/arm/exec.rs
rename to src/core/arm7tdmi/arm/exec.rs
index 58eaddb..a5267a1 100644
--- a/src/arm7tdmi/arm/exec.rs
+++ b/src/core/arm7tdmi/arm/exec.rs
@@ -1,11 +1,13 @@
 use crate::bit::BitIndex;
 
-use crate::arm7tdmi::alu::*;
-use crate::arm7tdmi::bus::Bus;
-use crate::arm7tdmi::cpu::{Core, CpuExecResult};
-use crate::arm7tdmi::exception::Exception;
-use crate::arm7tdmi::psr::RegPSR;
-use crate::arm7tdmi::{Addr, CpuError, CpuMode, CpuResult, CpuState, DecodedInstruction, REG_PC};
+use crate::core::arm7tdmi::alu::*;
+use crate::core::arm7tdmi::bus::Bus;
+use crate::core::arm7tdmi::cpu::{Core, CpuExecResult};
+use crate::core::arm7tdmi::exception::Exception;
+use crate::core::arm7tdmi::psr::RegPSR;
+use crate::core::arm7tdmi::{
+    Addr, CpuError, CpuMode, CpuResult, CpuState, DecodedInstruction, REG_PC,
+};
 
 use super::*;
 
diff --git a/src/arm7tdmi/arm/mod.rs b/src/core/arm7tdmi/arm/mod.rs
similarity index 99%
rename from src/arm7tdmi/arm/mod.rs
rename to src/core/arm7tdmi/arm/mod.rs
index 9eafb4e..09652fd 100644
--- a/src/arm7tdmi/arm/mod.rs
+++ b/src/core/arm7tdmi/arm/mod.rs
@@ -2,7 +2,7 @@ pub mod display;
 pub mod exec;
 
 use super::alu::*;
-use crate::arm7tdmi::{Addr, InstructionDecoder, InstructionDecoderError};
+use crate::core::arm7tdmi::{Addr, InstructionDecoder, InstructionDecoderError};
 
 use crate::bit::BitIndex;
 use crate::byteorder::{LittleEndian, ReadBytesExt};
@@ -351,7 +351,7 @@ impl ArmInstruction {
 /// All instructions constants were generated using an ARM assembler.
 mod tests {
     use super::*;
-    use crate::arm7tdmi::*;
+    use crate::core::arm7tdmi::*;
     use crate::sysbus::BoxedMemory;
 
     #[test]
diff --git a/src/arm7tdmi/bus.rs b/src/core/arm7tdmi/bus.rs
similarity index 100%
rename from src/arm7tdmi/bus.rs
rename to src/core/arm7tdmi/bus.rs
diff --git a/src/arm7tdmi/cpu.rs b/src/core/arm7tdmi/cpu.rs
similarity index 100%
rename from src/arm7tdmi/cpu.rs
rename to src/core/arm7tdmi/cpu.rs
diff --git a/src/arm7tdmi/exception.rs b/src/core/arm7tdmi/exception.rs
similarity index 100%
rename from src/arm7tdmi/exception.rs
rename to src/core/arm7tdmi/exception.rs
diff --git a/src/arm7tdmi/mod.rs b/src/core/arm7tdmi/mod.rs
similarity index 100%
rename from src/arm7tdmi/mod.rs
rename to src/core/arm7tdmi/mod.rs
diff --git a/src/arm7tdmi/psr.rs b/src/core/arm7tdmi/psr.rs
similarity index 100%
rename from src/arm7tdmi/psr.rs
rename to src/core/arm7tdmi/psr.rs
diff --git a/src/arm7tdmi/thumb/display.rs b/src/core/arm7tdmi/thumb/display.rs
similarity index 99%
rename from src/arm7tdmi/thumb/display.rs
rename to src/core/arm7tdmi/thumb/display.rs
index ba59cc9..79c6134 100644
--- a/src/arm7tdmi/thumb/display.rs
+++ b/src/core/arm7tdmi/thumb/display.rs
@@ -3,7 +3,7 @@ use std::fmt;
 use crate::bit::BitIndex;
 
 use super::*;
-use crate::arm7tdmi::*;
+use crate::core::arm7tdmi::*;
 
 impl ThumbInstruction {
     fn fmt_thumb_move_shifted_reg(&self, f: &mut fmt::Formatter) -> fmt::Result {
diff --git a/src/arm7tdmi/thumb/exec.rs b/src/core/arm7tdmi/thumb/exec.rs
similarity index 99%
rename from src/arm7tdmi/thumb/exec.rs
rename to src/core/arm7tdmi/thumb/exec.rs
index dcbf722..6937ce3 100644
--- a/src/arm7tdmi/thumb/exec.rs
+++ b/src/core/arm7tdmi/thumb/exec.rs
@@ -1,6 +1,6 @@
-use crate::arm7tdmi::bus::Bus;
-use crate::arm7tdmi::cpu::{Core, CpuExecResult};
-use crate::arm7tdmi::*;
+use crate::core::arm7tdmi::bus::Bus;
+use crate::core::arm7tdmi::cpu::{Core, CpuExecResult};
+use crate::core::arm7tdmi::*;
 
 use super::*;
 fn push(cpu: &mut Core, bus: &mut Bus, r: usize) {
diff --git a/src/arm7tdmi/thumb/mod.rs b/src/core/arm7tdmi/thumb/mod.rs
similarity index 99%
rename from src/arm7tdmi/thumb/mod.rs
rename to src/core/arm7tdmi/thumb/mod.rs
index ed5a167..a7c94c1 100644
--- a/src/arm7tdmi/thumb/mod.rs
+++ b/src/core/arm7tdmi/thumb/mod.rs
@@ -348,7 +348,7 @@ impl ThumbInstruction {
 /// All instructions constants were generated using an ARM assembler.
 mod tests {
     use super::*;
-    use crate::arm7tdmi::{Core, Bus};
+    use crate::core::arm7tdmi::{Bus, Core};
     use crate::sysbus::BoxedMemory;
 
     #[test]
diff --git a/src/cartridge.rs b/src/core/cartridge.rs
similarity index 97%
rename from src/cartridge.rs
rename to src/core/cartridge.rs
index 7ec350f..b3a5fd9 100644
--- a/src/cartridge.rs
+++ b/src/core/cartridge.rs
@@ -2,13 +2,12 @@ use std::str::from_utf8;
 
 use byteorder::{LittleEndian, ReadBytesExt, WriteBytesExt};
 
-use crate::arm7tdmi::{
+use super::arm7tdmi::{
     bus::{Bus, MemoryAccess, MemoryAccessWidth},
     Addr,
 };
-use crate::sysbus::WaitState;
+use super::sysbus::WaitState;
 use crate::util::read_bin_file;
-use crate::GBAError;
 
 /// From GBATEK
 ///
@@ -79,7 +78,7 @@ pub struct Cartridge {
 impl Cartridge {
     const MIN_SIZE: usize = 4 * 1024 * 1024;
 
-    pub fn load(path: &str) -> Result<Cartridge, GBAError> {
+    pub fn load(path: &str) -> Result<Cartridge, ::std::io::Error> {
         let mut rom_bin = read_bin_file(path)?;
         if rom_bin.len() < Cartridge::MIN_SIZE {
             rom_bin.resize_with(Cartridge::MIN_SIZE, Default::default);
diff --git a/src/dma.rs b/src/core/dma.rs
similarity index 100%
rename from src/dma.rs
rename to src/core/dma.rs
diff --git a/src/gba.rs b/src/core/gba.rs
similarity index 98%
rename from src/gba.rs
rename to src/core/gba.rs
index e5fcbaf..57175cb 100644
--- a/src/gba.rs
+++ b/src/core/gba.rs
@@ -7,8 +7,8 @@ use super::gpu::*;
 use super::interrupt::*;
 use super::ioregs::consts::*;
 use super::sysbus::SysBus;
-
-use super::{EmuIoDev, GBAError, GBAResult};
+use super::EmuIoDev;
+use super::{GBAError, GBAResult};
 
 pub struct GameBoyAdvance {
     pub cpu: Core,
diff --git a/src/gpu.rs b/src/core/gpu.rs
similarity index 98%
rename from src/gpu.rs
rename to src/core/gpu.rs
index 2be5edb..0c115d1 100644
--- a/src/gpu.rs
+++ b/src/core/gpu.rs
@@ -145,7 +145,7 @@ use GpuState::*;
 
 pub struct Gpu {
     cycles: usize,
-    pub pixeldata: [Rgb15; 256 * 256],
+    pub pixeldata: [Rgb15; 512 * 512],
     pub state: GpuState,
     pub current_scanline: usize, // VCOUNT
 }
@@ -168,7 +168,7 @@ impl Gpu {
             state: HDraw,
             current_scanline: 0,
             cycles: 0,
-            pixeldata: [Rgb15::from(0); 256 * 256],
+            pixeldata: [Rgb15::from(0); 512 * 512],
         }
     }
 
@@ -300,7 +300,7 @@ impl Gpu {
                         self.get_palette_color(sysbus, index as u32, 0)
                     }
                 };
-                self.pixeldata[((px + tile_x) as usize) + py * 256] = color;
+                self.pixeldata[((px + tile_x) as usize) + py * 512] = color;
             }
             px += 8;
             if px == bgcnt.screen_width as u32 {
@@ -313,7 +313,7 @@ impl Gpu {
         let page: u32 = match dispcnt.display_frame {
             0 => 0x0600_0000,
             1 => 0x0600_a000,
-            _ => unreachable!()
+            _ => unreachable!(),
         };
 
         let y = self.current_scanline;
@@ -322,7 +322,7 @@ impl Gpu {
             let bitmap_index = x + y * Self::DISPLAY_WIDTH;
             let bitmap_addr = page + (bitmap_index as u32);
             let index = sysbus.read_8(bitmap_addr as Addr) as u32;
-            self.pixeldata[x + y * 256] = self.get_palette_color(sysbus, index, 0);
+            self.pixeldata[x + y * 512] = self.get_palette_color(sysbus, index, 0);
         }
     }
 
diff --git a/src/interrupt.rs b/src/core/interrupt.rs
similarity index 100%
rename from src/interrupt.rs
rename to src/core/interrupt.rs
diff --git a/src/ioregs.rs b/src/core/ioregs.rs
similarity index 99%
rename from src/ioregs.rs
rename to src/core/ioregs.rs
index a2e8cfd..3a4faa0 100644
--- a/src/ioregs.rs
+++ b/src/core/ioregs.rs
@@ -2,7 +2,7 @@ use std::io;
 
 use byteorder::{LittleEndian, ReadBytesExt, WriteBytesExt};
 
-use crate::arm7tdmi::{Addr, Bus, MemoryAccess};
+use crate::core::arm7tdmi::{Addr, Bus, MemoryAccess};
 
 pub mod consts {
     use super::*;
diff --git a/src/core/mod.rs b/src/core/mod.rs
new file mode 100644
index 0000000..b117412
--- /dev/null
+++ b/src/core/mod.rs
@@ -0,0 +1,45 @@
+pub mod arm7tdmi;
+pub mod cartridge;
+pub mod gpu;
+pub mod sysbus;
+pub use sysbus::SysBus;
+pub mod interrupt;
+pub mod ioregs;
+pub use interrupt::Interrupt;
+pub mod gba;
+pub use gba::GameBoyAdvance;
+pub mod dma;
+pub mod palette;
+
+use crate::debugger;
+
+pub trait EmuIoDev {
+    fn step(&mut self, cycles: usize, sysbus: &mut SysBus) -> (usize, Option<Interrupt>);
+}
+
+#[derive(Debug)]
+pub enum GBAError {
+    IO(::std::io::Error),
+    CpuError(arm7tdmi::CpuError),
+    DebuggerError(debugger::DebuggerError),
+}
+
+pub type GBAResult<T> = Result<T, GBAError>;
+
+impl From<::std::io::Error> for GBAError {
+    fn from(err: ::std::io::Error) -> GBAError {
+        GBAError::IO(err)
+    }
+}
+
+impl From<arm7tdmi::CpuError> for GBAError {
+    fn from(err: arm7tdmi::CpuError) -> GBAError {
+        GBAError::CpuError(err)
+    }
+}
+
+impl From<debugger::DebuggerError> for GBAError {
+    fn from(err: debugger::DebuggerError) -> GBAError {
+        GBAError::DebuggerError(err)
+    }
+}
diff --git a/src/palette.rs b/src/core/palette.rs
similarity index 100%
rename from src/palette.rs
rename to src/core/palette.rs
diff --git a/src/sysbus.rs b/src/core/sysbus.rs
similarity index 100%
rename from src/sysbus.rs
rename to src/core/sysbus.rs
diff --git a/src/debugger/command.rs b/src/debugger/command.rs
index 7facecb..49c4e98 100644
--- a/src/debugger/command.rs
+++ b/src/debugger/command.rs
@@ -1,9 +1,11 @@
-use crate::arm7tdmi::bus::Bus;
-use crate::arm7tdmi::{Addr, CpuState};
+use crate::core::arm7tdmi::arm::ArmInstruction;
+use crate::core::arm7tdmi::bus::Bus;
+use crate::core::arm7tdmi::thumb::ThumbInstruction;
+use crate::core::arm7tdmi::{Addr, CpuState};
+use crate::core::gpu::*;
+use crate::core::ioregs::consts::*;
+use crate::core::GBAError;
 use crate::disass::Disassembler;
-use crate::ioregs::consts::*;
-use crate::gpu::*;
-use crate::GBAError;
 
 use super::palette_view::create_palette_view;
 use super::render_view::create_render_view;
@@ -137,9 +139,6 @@ impl Command {
                 hexdump::hexdump(&bytes[0..nbytes]);
             }
             Disass(mode, addr, n) => {
-                use crate::arm7tdmi::arm::ArmInstruction;
-                use crate::arm7tdmi::thumb::ThumbInstruction;
-
                 let bytes = debugger.gba.sysbus.get_bytes(addr);
                 match mode {
                     DisassMode::ModeArm => {
diff --git a/src/debugger/mod.rs b/src/debugger/mod.rs
index 3f81feb..5068e7d 100644
--- a/src/debugger/mod.rs
+++ b/src/debugger/mod.rs
@@ -3,8 +3,8 @@ use rustyline::Editor;
 
 use colored::*;
 
-use super::arm7tdmi::{Addr, Bus, CpuError};
-use super::GameBoyAdvance;
+use super::core::arm7tdmi::{Addr, Bus, CpuError};
+use super::core::GameBoyAdvance;
 
 mod parser;
 use parser::{parse_expr, DerefType, Expr, Value};
diff --git a/src/debugger/palette_view.rs b/src/debugger/palette_view.rs
index c037573..f1deb62 100644
--- a/src/debugger/palette_view.rs
+++ b/src/debugger/palette_view.rs
@@ -3,7 +3,7 @@ use sdl2::pixels::Color;
 use sdl2::rect::{Point, Rect};
 use sdl2::render::Canvas;
 
-use super::super::palette::{Palette, Rgb15};
+use crate::core::palette::{Palette, Rgb15};
 
 const PALETTE_RECT_WIDTH: u32 = 20;
 
diff --git a/src/debugger/render_view.rs b/src/debugger/render_view.rs
index 854cdc4..2bc0e5e 100644
--- a/src/debugger/render_view.rs
+++ b/src/debugger/render_view.rs
@@ -4,8 +4,8 @@ use sdl2::event::Event;
 use sdl2::pixels::Color;
 use sdl2::rect::Point;
 
-use crate::gba::GameBoyAdvance;
-use crate::gpu::Gpu;
+use crate::core::gba::GameBoyAdvance;
+use crate::core::gpu::Gpu;
 
 const SCREEN_WIDTH: u32 = Gpu::DISPLAY_WIDTH as u32;
 const SCREEN_HEIGHT: u32 = Gpu::DISPLAY_HEIGHT as u32;
@@ -39,7 +39,7 @@ pub fn create_render_view(gba: &GameBoyAdvance) {
 
         for y in 0..Gpu::DISPLAY_HEIGHT {
             for x in 0..Gpu::DISPLAY_WIDTH {
-                let index = (x as usize) + (y as usize) * (256 as usize);
+                let index = (x as usize) + (y as usize) * (512 as usize);
                 let color = gba.gpu.pixeldata[index];
                 let rgb24: Color = color.into();
                 canvas.set_draw_color(rgb24);
diff --git a/src/debugger/tile_view.rs b/src/debugger/tile_view.rs
index 2b09bde..56277fb 100644
--- a/src/debugger/tile_view.rs
+++ b/src/debugger/tile_view.rs
@@ -5,12 +5,12 @@ use sdl2::pixels::Color;
 use sdl2::rect::{Point, Rect};
 use sdl2::render::Canvas;
 
-use crate::arm7tdmi::bus::Bus;
-use crate::gba::GameBoyAdvance;
-use crate::ioregs::consts::*;
-use crate::gpu::*;
-use crate::palette::*;
-use crate::sysbus::SysBus;
+use crate::core::arm7tdmi::bus::Bus;
+use crate::core::gba::GameBoyAdvance;
+use crate::core::gpu::*;
+use crate::core::ioregs::consts::*;
+use crate::core::palette::*;
+use crate::core::sysbus::SysBus;
 
 impl Into<Color> for Rgb15 {
     fn into(self) -> Color {
@@ -100,7 +100,6 @@ pub fn create_tile_view(bg: u32, gba: &GameBoyAdvance) {
             }
         }
 
-
         canvas.set_draw_color(Color::RGB(00, 00, 00));
         canvas.clear();
 
diff --git a/src/disass.rs b/src/disass.rs
index eef3477..11b8c8c 100644
--- a/src/disass.rs
+++ b/src/disass.rs
@@ -1,6 +1,6 @@
 use std::marker::PhantomData;
 
-use super::arm7tdmi::{Addr, InstructionDecoder, InstructionDecoderError};
+use super::core::arm7tdmi::{Addr, InstructionDecoder, InstructionDecoderError};
 use std::io::ErrorKind;
 
 pub struct Disassembler<'a, D>
diff --git a/src/lib.rs b/src/lib.rs
index ab58e7d..22eade4 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -14,49 +14,7 @@ extern crate nom;
 extern crate ansi_term;
 extern crate colored; // not needed in Rust 2018
 
-pub mod arm7tdmi;
-pub mod cartridge;
+pub mod core;
 pub mod debugger;
 pub mod disass;
-pub mod gpu;
-pub mod sysbus;
-pub use sysbus::SysBus;
-pub mod interrupt;
-pub mod ioregs;
-pub use interrupt::Interrupt;
-pub mod gba;
-pub use gba::GameBoyAdvance;
-pub mod dma;
-pub mod palette;
 pub mod util;
-
-pub trait EmuIoDev {
-    fn step(&mut self, cycles: usize, sysbus: &mut SysBus) -> (usize, Option<Interrupt>);
-}
-
-#[derive(Debug)]
-pub enum GBAError {
-    IO(::std::io::Error),
-    CpuError(arm7tdmi::CpuError),
-    DebuggerError(debugger::DebuggerError),
-}
-
-pub type GBAResult<T> = Result<T, GBAError>;
-
-impl From<::std::io::Error> for GBAError {
-    fn from(err: ::std::io::Error) -> GBAError {
-        GBAError::IO(err)
-    }
-}
-
-impl From<arm7tdmi::CpuError> for GBAError {
-    fn from(err: arm7tdmi::CpuError) -> GBAError {
-        GBAError::CpuError(err)
-    }
-}
-
-impl From<debugger::DebuggerError> for GBAError {
-    fn from(err: debugger::DebuggerError) -> GBAError {
-        GBAError::DebuggerError(err)
-    }
-}