feat: stub 0xff40 and 0xff47

src/ppu.rs

@@ -1,20 +1,27 @@
 #[derive(Debug, Clone)]
 pub struct PPU {
-    lcdc: LCDControl,
+    pub lcd_control: LCDControl,
+    pub monochrome: Monochrome,
     pub vram: Box<[u8]>,
 }
 
 impl Default for PPU {
     fn default() -> Self {
         Self {
-            lcdc: Default::default(),
+            lcd_control: Default::default(),
+            monochrome: Default::default(),
             vram: vec![0; 8192].into_boxed_slice(),
         }
     }
 }
 
+#[derive(Debug, Clone, Copy, Default)]
+pub struct Monochrome {
+    pub bg_palette: BackgroundPalette,
+}
+
 #[derive(Debug, Default, Clone, Copy)]
-struct LCDControl {
+pub struct LCDControl {
     lcd_enable: bool, // Bit 7
     window_tile_map_select: bool,
     window_enable: bool,
@@ -52,3 +59,70 @@ impl From<LCDControl> for u8 {
             | lcdc.display_priority as u8
     }
 }
+
+#[derive(Debug, Clone, Copy)]
+enum GrayShade {
+    White,
+    LightGray,
+    DarkGray,
+    Black,
+}
+
+impl Default for GrayShade {
+    fn default() -> Self {
+        Self::White
+    }
+}
+
+impl From<u8> for GrayShade {
+    fn from(byte: u8) -> Self {
+        match byte {
+            0b00 => GrayShade::White,
+            0b01 => GrayShade::LightGray,
+            0b10 => GrayShade::DarkGray,
+            0b11 => GrayShade::Black,
+            _ => unreachable!("{:#04X} is not a valid Shade of Gray", byte),
+        }
+    }
+}
+
+impl From<GrayShade> for u8 {
+    fn from(shade: GrayShade) -> Self {
+        match shade {
+            GrayShade::White => 0b00,
+            GrayShade::LightGray => 0b01,
+            GrayShade::DarkGray => 0b10,
+            GrayShade::Black => 0b11,
+        }
+    }
+}
+
+#[derive(Debug, Clone, Copy, Default)]
+pub struct BackgroundPalette {
+    color3: GrayShade,
+    color2: GrayShade,
+    color1: GrayShade,
+    color0: GrayShade,
+}
+
+impl From<u8> for BackgroundPalette {
+    fn from(byte: u8) -> Self {
+        Self {
+            color3: (byte >> 6).into(),
+            color2: ((byte >> 4) & 0x03).into(),
+            color1: ((byte >> 2) & 0x03).into(),
+            color0: (byte & 0x03).into(),
+        }
+    }
+}
+
+impl From<BackgroundPalette> for u8 {
+    fn from(palette: BackgroundPalette) -> Self {
+        let color0: u8 = palette.color0.into();
+        let color1: u8 = palette.color1.into();
+        let color2: u8 = palette.color2.into();
+        let color3: u8 = palette.color0.into();
+
+        color3 << 6 | color2 << 4 | color1 << 2 | color0
+    }
+}