feat: new test rom and initial speed support

The double speed mode is still not available.

src/gb.rs

@@ -82,6 +82,13 @@ impl Display for GameBoyMode {
     }
 }
 
+#[cfg_attr(feature = "wasm", wasm_bindgen)]
+#[derive(Clone, Copy, PartialEq, Eq)]
+pub enum GameBoySpeed {
+    Normal = 0,
+    Double = 1,
+}
+
 #[cfg_attr(feature = "wasm", wasm_bindgen)]
 #[derive(Clone, Copy, PartialEq, Eq)]
 pub struct GameBoyConfig {

src/mmu.rs

 use crate::{
     apu::Apu,
     debugln,
-    gb::{GameBoyConfig, GameBoyMode},
+    gb::{GameBoyConfig, GameBoyMode, GameBoySpeed},
     pad::Pad,
     ppu::Ppu,
     rom::Cartridge,
@@ -29,6 +29,8 @@ pub struct Mmu {
     /// (CGB only).
     pub key0: u8,
 
+    pub speed: GameBoySpeed,
+
     /// Reference to the PPU (Pixel Processing Unit) that is going
     /// to be used both for VRAM reading/writing and to forward
     /// some of the access operations.
@@ -110,6 +112,7 @@ impl Mmu {
             ram_offset: 0x1000,
             ie: 0x0,
             key0: 0x0,
+            speed: GameBoySpeed::Normal,
             mode,
             gbc,
         }
@@ -253,7 +256,7 @@ impl Mmu {
                     0x4c => self.key0,
 
                     // 0xFF4D - KEY1 (CGB only)
-                    0x4d => todo!("CGB speed switch"),
+                    0x4d => (false as u8) | ((self.speed as u8) << 7),
 
                     // 0xFF50 - Boot active flag
                     0x50 => u8::from(self.boot_active),