Add nop instruction

src/cpu/instructions/misc.rs

@@ -7,4 +7,5 @@ pub enum MiscInstruction {
     ComplementCarryFlag,
     ComplementARegister,
     DecimalAdjustAccumulator,
+    Nop,
 }

src/cpu/parse/misc.rs

@@ -14,6 +14,7 @@ impl OpcodeParser for Parser {
             0x3F => Ok(build_complement_carry_flag_data()),
             0x27 => Ok(build_daa_data()),
             0x2F => Ok(build_complement_a_register_data()),
+            0x00 => Ok(build_nop_data()),
             _ => Err(super::Error::UnknownOpcode(opcode)),
         }
     }
@@ -37,3 +38,10 @@ fn build_daa_data() -> ParseOutput {
         1,
     )
 }
+
+fn build_nop_data() -> ParseOutput {
+    (
+        Instruction::Misc(MiscInstruction::Nop),
+        1,
+    )
+}

src/cpu/run/misc.rs

@@ -8,11 +8,16 @@ 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::SetCarryFlag => {
                 set_flags_in_carry_bit_instruction(processor, 1);
 
                 Ok(Cycles(4))
             }
+
             MiscInstruction::ComplementCarryFlag => {
                 let current_carry_flag = processor.registers.get_flag_bit(register::Flag::Carry);
                 let flipped = (current_carry_flag == 0).into();
@@ -21,6 +26,7 @@ impl Run for MiscInstruction {
 
                 Ok(Cycles(4))
             }
+
             MiscInstruction::ComplementARegister => {
                 let current_value = processor
                     .registers
@@ -38,6 +44,7 @@ impl Run for MiscInstruction {
 
                 Ok(Cycles(4))
             }
+
             MiscInstruction::DecimalAdjustAccumulator => {
                 let (adjusted_a_value, carry) = get_daa_value(&processor.registers);
 

tests/cpu/misc.rs

@@ -157,3 +157,17 @@ fn test_daa(
         (register::Flag::Zero, u8::from(expected_flags.zero))
     );
 }
+
+#[test]
+fn test_nop_executes_successfully() {
+    let mut processor = Processor::default();
+    let data = [0x00, 0x06];
+
+    let (ins, extra_data) = Instruction::from_data(&data).expect("could not parse instruction");
+
+    assert_eq!(extra_data, &[0x06]);
+    processor.run_instruction(ins);
+
+    // uhhh it does nothing
+    assert_eq!(processor.num_cycles, 4);
+}