diff --git a/src/backend/sdl2_backend.rs b/src/backend/sdl2_backend.rs
index e604e0f..234bc6e 100644
--- a/src/backend/sdl2_backend.rs
+++ b/src/backend/sdl2_backend.rs
@@ -1,5 +1,5 @@
-use std::time;
 use std::convert::TryFrom;
+use std::time;
 
 use crate::bit::BitIndex;
 
@@ -120,7 +120,6 @@ impl EmulatorBackend for Sdl2Backend {
     }
 }
 
-
 fn keycode_to_keypad(keycode: Keycode) -> Option<keypad::Keys> {
     match keycode {
         Keycode::Up => Some(keypad::Keys::Up),
@@ -129,4 +128,4 @@ fn keycode_to_keypad(keycode: Keycode) -> Option<keypad::Keys> {
         Keycode::Right => Some(keypad::Keys::Right),
         _ => None,
     }
-}
\ No newline at end of file
+}
diff --git a/src/core/gpu/mod.rs b/src/core/gpu/mod.rs
index 51d2e26..f9878a1 100644
--- a/src/core/gpu/mod.rs
+++ b/src/core/gpu/mod.rs
@@ -1,16 +1,19 @@
 use std::fmt;
 
 use super::arm7tdmi::{Addr, Bus};
-use super::palette::{PixelFormat, Rgb15};
+pub use super::palette::{PixelFormat, Rgb15};
 use super::*;
 
 use crate::bitfield::Bit;
 use crate::num::FromPrimitive;
 
-const VRAM_ADDR: Addr = 0x0600_0000;
+mod regs;
+pub use regs::*;
+
+pub const VRAM_ADDR: Addr = 0x0600_0000;
 
 #[derive(Debug, Primitive, Clone, Copy)]
-enum BGMode {
+pub enum BGMode {
     BGMode0 = 0,
     BGMode1 = 1,
     BGMode2 = 2,
@@ -25,88 +28,6 @@ impl From<u16> for BGMode {
     }
 }
 
-bitfield! {
-    pub struct DisplayControl(u16);
-    impl Debug;
-    u16;
-    into BGMode, mode, set_mode: 2, 0;
-    display_frame, set_display_frame: 4, 4;
-    hblank_interval_free, _: 5;
-    obj_character_vram_mapping, _: 6;
-    forst_vblank, _: 7;
-    disp_bg0, _ : 8;
-    disp_bg1, _ : 9;
-    disp_bg2, _ : 10;
-    disp_bg3, _ : 11;
-    disp_obj, _ : 12;
-    disp_window0, _ : 13;
-    disp_window1, _ : 14;
-    disp_obj_window, _ : 15;
-}
-
-impl DisplayControl {
-    fn disp_bg(&self, bg: usize) -> bool {
-        self.0.bit(8 + bg)
-    }
-}
-
-bitfield! {
-    pub struct DisplayStatus(u16);
-    impl Debug;
-    u16;
-    get_vblank, set_vblank: 0;
-    get_hblank, set_hblank: 1;
-    get_vcount, set_vcount: 2;
-    vblank_irq_enable, _ : 3;
-    hblank_irq_enable, _ : 4;
-    vcount_irq_enable, _ : 5;
-    vcount_setting, _ : 15, 8;
-}
-
-bitfield! {
-    #[derive(Copy, Clone)]
-    pub struct BgControl(u16);
-    impl Debug;
-    u16;
-    bg_priority, _: 1, 0;
-    character_base_block, _: 3, 2;
-    moasic, _ : 6;
-    palette256, _ : 7;
-    screen_base_block, _: 12, 8;
-    affine_wraparound, _: 13;
-    bg_size, _ : 15, 14;
-}
-
-const SCREEN_BLOCK_SIZE: u32 = 0x800;
-
-impl BgControl {
-    pub fn char_block(&self) -> Addr {
-        VRAM_ADDR + (self.character_base_block() as u32) * 0x4000
-    }
-
-    pub fn screen_block(&self) -> Addr {
-        VRAM_ADDR + (self.screen_base_block() as u32) * SCREEN_BLOCK_SIZE
-    }
-
-    fn size_regular(&self) -> (u32, u32) {
-        match self.bg_size() {
-            0b00 => (256, 256),
-            0b01 => (512, 256),
-            0b10 => (256, 512),
-            0b11 => (512, 512),
-            _ => unreachable!(),
-        }
-    }
-
-    pub fn tile_format(&self) -> (u32, PixelFormat) {
-        if self.palette256() {
-            (2 * Gpu::TILE_SIZE, PixelFormat::BPP8)
-        } else {
-            (Gpu::TILE_SIZE, PixelFormat::BPP4)
-        }
-    }
-}
-
 #[derive(Debug, PartialEq, Copy, Clone)]
 pub enum GpuState {
     HDraw = 0,
diff --git a/src/core/gpu/regs.rs b/src/core/gpu/regs.rs
new file mode 100644
index 0000000..78601ff
--- /dev/null
+++ b/src/core/gpu/regs.rs
@@ -0,0 +1,83 @@
+use super::*;
+
+bitfield! {
+    pub struct DisplayControl(u16);
+    impl Debug;
+    u16;
+    pub into BGMode, mode, set_mode: 2, 0;
+    pub display_frame, set_display_frame: 4, 4;
+    pub hblank_interval_free, _: 5;
+    pub obj_character_vram_mapping, _: 6;
+    pub forst_vblank, _: 7;
+    pub disp_bg0, _ : 8;
+    pub disp_bg1, _ : 9;
+    pub disp_bg2, _ : 10;
+    pub disp_bg3, _ : 11;
+    pub disp_obj, _ : 12;
+    pub disp_window0, _ : 13;
+    pub disp_window1, _ : 14;
+    pub disp_obj_window, _ : 15;
+}
+
+impl DisplayControl {
+    pub fn disp_bg(&self, bg: usize) -> bool {
+        self.0.bit(8 + bg)
+    }
+}
+
+bitfield! {
+    pub struct DisplayStatus(u16);
+    impl Debug;
+    u16;
+    pub get_vblank, set_vblank: 0;
+    pub get_hblank, set_hblank: 1;
+    pub get_vcount, set_vcount: 2;
+    pub vblank_irq_enable, _ : 3;
+    pub hblank_irq_enable, _ : 4;
+    pub vcount_irq_enable, _ : 5;
+    pub vcount_setting, _ : 15, 8;
+}
+
+bitfield! {
+    #[derive(Copy, Clone)]
+    pub struct BgControl(u16);
+    impl Debug;
+    u16;
+    pub bg_priority, _: 1, 0;
+    pub character_base_block, _: 3, 2;
+    pub moasic, _ : 6;
+    pub palette256, _ : 7;
+    pub screen_base_block, _: 12, 8;
+    pub affine_wraparound, _: 13;
+    pub bg_size, _ : 15, 14;
+}
+
+pub const SCREEN_BLOCK_SIZE: u32 = 0x800;
+
+impl BgControl {
+    pub fn char_block(&self) -> u32 {
+        VRAM_ADDR + (self.character_base_block() as u32) * 0x4000
+    }
+
+    pub fn screen_block(&self) -> u32 {
+        VRAM_ADDR + (self.screen_base_block() as u32) * SCREEN_BLOCK_SIZE
+    }
+
+    pub fn size_regular(&self) -> (u32, u32) {
+        match self.bg_size() {
+            0b00 => (256, 256),
+            0b01 => (512, 256),
+            0b10 => (256, 512),
+            0b11 => (512, 512),
+            _ => unreachable!(),
+        }
+    }
+
+    pub fn tile_format(&self) -> (u32, PixelFormat) {
+        if self.palette256() {
+            (2 * Gpu::TILE_SIZE, PixelFormat::BPP8)
+        } else {
+            (Gpu::TILE_SIZE, PixelFormat::BPP4)
+        }
+    }
+}