Add support for enabling/disabling interrupts

src/cpu.rs

@@ -15,6 +15,7 @@ pub struct Processor {
     pub registers: Registers,
     pub memory: Memory,
     pub num_cycles: u128,
+    interrupt_enable_pending: bool,
 }
 
 impl Processor {
@@ -32,9 +33,17 @@ impl Processor {
         let (instruction, bytes_read) =
             parse::next_instruction(&memory_view).expect("invalid instruction");
 
+        let interrupt_enable_pending_already = self.interrupt_enable_pending;
         self.run_instruction(instruction);
 
-        let (next_pc, _carry) = pc.overflowing_add(bytes_read);
+        // EI does not work until after the following instruction, so we check after running an instruction if
+        // this is true
+        if interrupt_enable_pending_already && self.interrupt_enable_pending {
+            self.interrupt_enable_pending = false;
+            self.registers.enable_interrupts();
+        }
+
+        let next_pc = pc.wrapping_add(bytes_read);
         self.registers.program_counter = next_pc;
     }
 
@@ -51,6 +60,20 @@ impl Processor {
         self.num_cycles += u128::from(run_res.unwrap().0);
     }
 
+    pub fn enable_interrupts(&mut self) {
+        self.interrupt_enable_pending = true;
+    }
+
+    pub fn disable_interrupts(&mut self) {
+        self.interrupt_enable_pending = false;
+        self.registers.disable_interrupts();
+    }
+
+    #[must_use]
+    pub fn interrupts_enabled(&mut self) -> bool {
+        self.registers.interrupts_enabled()
+    }
+
     fn load_from_register_to_register_address(
         &mut self,
         register_with_dst_address: register::Combined,

src/cpu/instructions/misc.rs

@@ -8,4 +8,6 @@ pub enum MiscInstruction {
     ComplementARegister,
     DecimalAdjustAccumulator,
     Nop,
+    EnableInterrupts,
+    DisableInterrupts,
 }

src/cpu/parse/misc.rs

@@ -15,6 +15,8 @@ impl OpcodeParser for Parser {
             0x27 => Ok(build_daa_data()),
             0x2F => Ok(build_complement_a_register_data()),
             0x00 => Ok(build_nop_data()),
+            0xFB => Ok(build_enable_interrupts_data()),
+            0xF3 => Ok(build_disable_interrupts_data()),
             _ => Err(super::Error::UnknownOpcode(opcode)),
         }
     }
@@ -40,8 +42,13 @@ fn build_daa_data() -> ParseOutput {
 }
 
 fn build_nop_data() -> ParseOutput {
-    (
-        Instruction::Misc(MiscInstruction::Nop),
-        1,
-    )
+    (Instruction::Misc(MiscInstruction::Nop), 1)
+}
+
+fn build_enable_interrupts_data() -> ParseOutput {
+    (Instruction::Misc(MiscInstruction::EnableInterrupts), 1)
+}
+
+fn build_disable_interrupts_data() -> ParseOutput {
+    (Instruction::Misc(MiscInstruction::DisableInterrupts), 1)
 }

src/cpu/run/misc.rs

@@ -8,9 +8,7 @@ use super::{Cycles, Run};
 impl Run for MiscInstruction {
     fn run_on(&self, processor: &mut Processor) -> Result<Cycles, Error> {
         match *self {
-            MiscInstruction::Nop => {
-                Ok(Cycles(4))
-            }
+            MiscInstruction::Nop => Ok(Cycles(4)),
 
             MiscInstruction::SetCarryFlag => {
                 set_flags_in_carry_bit_instruction(processor, 1);
@@ -66,6 +64,18 @@ impl Run for MiscInstruction {
 
                 Ok(Cycles(4))
             }
+
+            MiscInstruction::EnableInterrupts => {
+                processor.enable_interrupts();
+
+                Ok(Cycles(4))
+            },
+
+            MiscInstruction::DisableInterrupts => {
+                processor.disable_interrupts();
+
+                Ok(Cycles(4))
+            }
         }
     }
 }

src/register.rs

@@ -66,6 +66,7 @@ pub struct Registers {
     pub program_counter: u16,
     // the "F" register and the "flags" register are the same register
     flags: u8,
+    interrupts_enabled: bool,
 }
 
 impl Flag {
@@ -99,6 +100,7 @@ impl Default for Registers {
             e: 0,
             h: 0,
             l: 0,
+            interrupts_enabled: false,
             stack_pointer: 0,
             program_counter: INITIAL_PROGRAM_COUNTER_VALUE,
             flags: 0,
@@ -264,6 +266,19 @@ impl Registers {
             Combined::HL => (&mut self.h, &mut self.l),
         }
     }
+
+    pub(super) fn enable_interrupts(&mut self) {
+        self.interrupts_enabled = true;
+    }
+
+    pub(super) fn disable_interrupts(&mut self) {
+        self.interrupts_enabled = false;
+    }
+
+    #[must_use]
+    pub fn interrupts_enabled(&self) -> bool {
+        self.interrupts_enabled
+    }
 }
 
 #[cfg(test)]

tests/cpu/misc.rs

@@ -171,3 +171,69 @@ fn test_nop_executes_successfully() {
     // uhhh it does nothing
     assert_eq!(processor.num_cycles, 4);
 }
+
+#[test]
+fn test_enable_interrupts_enables_interrupts_on_the_following_instruction() {
+    let mut processor = Processor::default();
+
+    [
+        // Enable interrupts
+        0xFB, // Nop
+        0x00,
+    ]
+    .iter()
+    .copied()
+    .enumerate()
+    .for_each(|(idx, opcode)| {
+        processor
+            .memory
+            .set(
+                usize::from(processor.registers.program_counter) + idx,
+                opcode,
+            )
+            .expect("could not program data");
+    });
+
+    assert!(!processor.interrupts_enabled());
+
+    processor.run_next_instruction();
+    assert!(!processor.interrupts_enabled());
+
+    processor.run_next_instruction();
+    assert!(processor.interrupts_enabled());
+}
+
+#[test]
+fn test_disable_interrupts_disables_interrupts_once_enabled() {
+    let mut processor = Processor::default();
+
+    [
+        // Enable interrupts
+        0xFB, // Nop
+        0x00,
+        0xF3,
+    ]
+    .iter()
+    .copied()
+    .enumerate()
+    .for_each(|(idx, opcode)| {
+        processor
+            .memory
+            .set(
+                usize::from(processor.registers.program_counter) + idx,
+                opcode,
+            )
+            .expect("could not program data");
+    });
+
+    assert!(!processor.interrupts_enabled());
+
+    processor.run_next_instruction();
+    assert!(!processor.interrupts_enabled());
+
+    processor.run_next_instruction();
+    assert!(processor.interrupts_enabled());
+
+    processor.run_next_instruction();
+    assert!(!processor.interrupts_enabled());
+}