diff --git a/rustboyadvance-core/src/gpu/mod.rs b/rustboyadvance-core/src/gpu/mod.rs
index 65fa079..fbd4b1c 100644
--- a/rustboyadvance-core/src/gpu/mod.rs
+++ b/rustboyadvance-core/src/gpu/mod.rs
@@ -5,9 +5,10 @@ use std::rc::Rc;
 use serde::{Deserialize, Serialize};
 
 use super::interrupt::IrqBitmask;
+pub use super::sysbus::consts::*;
 use super::sysbus::{BoxedMemory, SysBus};
-use super::Bus;
 use super::VideoInterface;
+use super::{Addr, Bus};
 
 use crate::bitfield::Bit;
 use crate::num::FromPrimitive;
@@ -30,11 +31,11 @@ pub use regs::*;
 
 #[allow(unused)]
 pub mod consts {
+    pub use super::VRAM_ADDR;
     pub const VIDEO_RAM_SIZE: usize = 128 * 1024;
     pub const PALETTE_RAM_SIZE: usize = 1 * 1024;
     pub const OAM_SIZE: usize = 1 * 1024;
 
-    pub const VRAM_ADDR: u32 = 0x0600_0000;
     pub const DISPLAY_WIDTH: usize = 240;
     pub const DISPLAY_HEIGHT: usize = 160;
     pub const VBLANK_LINES: usize = 68;
@@ -203,6 +204,68 @@ pub struct Gpu {
     pub(super) frame_buffer: Vec<u32>,
 }
 
+impl Bus for Gpu {
+    fn read_8(&self, addr: Addr) -> u8 {
+        let page = (addr >> 24) as usize;
+        match page {
+            PAGE_PALRAM => self.palette_ram.read_8(addr & 0x3ff),
+            PAGE_VRAM => {
+                // complicated
+                let mut ofs = addr & ((VIDEO_RAM_SIZE as u32) - 1);
+                if ofs > 0x18000 {
+                    ofs -= 0x8000;
+                }
+                self.vram.read_8(ofs)
+            }
+            PAGE_OAM => self.oam.read_8(addr & 0x3ff),
+            _ => unreachable!(),
+        }
+    }
+
+    fn write_16(&mut self, addr: Addr, value: u16) {
+        let page = (addr >> 24) as usize;
+        match page {
+            PAGE_PALRAM => self.palette_ram.write_16(addr & 0x3fe, value),
+            PAGE_VRAM => {
+                let mut ofs = addr & ((VIDEO_RAM_SIZE as u32) - 1);
+                if ofs > 0x18000 {
+                    ofs -= 0x8000;
+                }
+                self.vram.write_16(ofs, value)
+            }
+            PAGE_OAM => self.oam.write_16(addr & 0x3fe, value),
+            _ => unreachable!(),
+        }
+    }
+
+    fn write_8(&mut self, addr: Addr, value: u8) {
+        fn expand_value(value: u8) -> u16 {
+            (value as u16) * 0x101
+        }
+
+        let page = (addr >> 24) as usize;
+        match page {
+            PAGE_PALRAM => self.oam.write_16(addr & 0x3fe, expand_value(value)),
+            PAGE_VRAM => {
+                let mut ofs = addr & ((VIDEO_RAM_SIZE as u32) - 1);
+                if ofs > 0x18000 {
+                    ofs -= 0x8000;
+                }
+                let obj_offset = if self.dispcnt.mode() >= 3 {
+                    0x14000
+                } else {
+                    0x10000
+                };
+                if ofs < obj_offset {
+                    self.vram.write_16(ofs & !1, expand_value(value));
+                }
+            }
+            PAGE_OAM => { /* OAM can't be written with 8bit store */ }
+            _ => unreachable!(),
+        };
+    }
+}
+
 impl Gpu {
     pub fn new() -> Gpu {
         Gpu {
diff --git a/rustboyadvance-core/src/sysbus.rs b/rustboyadvance-core/src/sysbus.rs
index bbeb49a..c22056e 100644
--- a/rustboyadvance-core/src/sysbus.rs
+++ b/rustboyadvance-core/src/sysbus.rs
@@ -255,15 +255,7 @@ macro_rules! memory_map {
                 };
                 $sb.io.$read_fn(addr)
             }
-            PALRAM_ADDR => $sb.io.gpu.palette_ram.$read_fn($addr & 0x3ff),
-            VRAM_ADDR => {
-                let mut ofs = $addr & ((VIDEO_RAM_SIZE as u32) - 1);
-                if ofs > 0x18000 {
-                    ofs -= 0x8000;
-                }
-                $sb.io.gpu.vram.$read_fn(ofs)
-            }
-            OAM_ADDR => $sb.io.gpu.oam.$read_fn($addr & 0x3ff),
+            PALRAM_ADDR | VRAM_ADDR | OAM_ADDR => $sb.io.gpu.$read_fn($addr),
             GAMEPAK_WS0_LO | GAMEPAK_WS0_HI | GAMEPAK_WS1_LO | GAMEPAK_WS1_HI | GAMEPAK_WS2_LO => {
                 $sb.cartridge.$read_fn($addr)
             }
@@ -289,15 +281,7 @@ macro_rules! memory_map {
                 };
                 $sb.io.$write_fn(addr, $value)
             }
-            PALRAM_ADDR => $sb.io.gpu.palette_ram.$write_fn($addr & 0x3ff, $value),
-            VRAM_ADDR => {
-                let mut ofs = $addr & ((VIDEO_RAM_SIZE as u32) - 1);
-                if ofs > 0x18000 {
-                    ofs -= 0x8000;
-                }
-                $sb.io.gpu.vram.$write_fn(ofs, $value)
-            }
-            OAM_ADDR => $sb.io.gpu.oam.$write_fn($addr & 0x3ff, $value),
+            PALRAM_ADDR | VRAM_ADDR | OAM_ADDR => $sb.io.gpu.$write_fn($addr, $value),
             GAMEPAK_WS0_LO | GAMEPAK_WS0_HI => {}
             GAMEPAK_WS2_HI => $sb.cartridge.$write_fn($addr, $value),
             SRAM_LO | SRAM_HI => $sb.cartridge.$write_fn($addr, $value),