fix ie behaviour

src/processor/memory/interrupts.rs

@@ -40,21 +40,32 @@ pub enum Interrupt {
     Joypad,
 }
 
-#[derive(Default)]
 pub struct Interrupts {
     // 0xFFFF
     enable_register: InterruptRegister,
+    enable_register_unused: u8,
     // 0xFF0F
     flag_register: InterruptRegister,
 }
 
+impl Default for Interrupts {
+    fn default() -> Self {
+        Self {
+            enable_register: Default::default(),
+            enable_register_unused: 0b11100000,
+            flag_register: Default::default(),
+        }
+    }
+}
+
 impl Interrupts {
     pub fn get_enable_register(&self) -> u8 {
-        0b11100000 | self.enable_register.as_register()
+        self.enable_register_unused | self.enable_register.as_register()
     }
 
     pub(super) fn set_enable_register(&mut self, data: u8) {
         self.enable_register.set_from_bits(data);
+        self.enable_register_unused = data & 0b11100000;
     }
 
     pub fn get_flag_register(&self) -> u8 {