Model the keypad

Former-commit-id: 4f38fa754e3ee809a7386351297decb2d7f1451f

src/core/keypad.rs

@@ -0,0 +1,33 @@
+#[derive(Debug, Primitive, PartialEq)]
+#[repr(u8)]
+pub enum Keys {
+    ButtonA = 0,
+    ButtonB = 1,
+    Select = 2,
+    Start = 3,
+    Right = 4,
+    Left = 5,
+    Up = 6,
+    Down = 7,
+    ButtonR = 8,
+    ButtonL = 9,
+}
+
+pub const NUM_KEYS: usize = 10;
+pub const KEYINPUT_ALL_RELEASED: u16 = 0b1111111111;
+
+#[derive(Debug, Primitive, PartialEq)]
+#[repr(u8)]
+pub enum KeyState {
+    Pressed = 0,
+    Released = 1,
+}
+
+impl Into<bool> for KeyState {
+    fn into(self) -> bool {
+        match self {
+            KeyState::Pressed => false,
+            KeyState::Released => true,
+        }
+    }
+}