Decode ld r8, [hl] opcode

This opcode is treated differently from ld r8, n8
because it requires an extra machine cycle to pull
data from memory.

src/cpu.rs

@@ -88,6 +88,7 @@ impl SharpSM83 {
  Opcode::NOP => self.no_op(),
  Opcode::LDRI8(dest) => self.ld_r_n8(dest, bus),
  Opcode::Unimplemented(_) => {}
+ _ => {}
  }
  }
 

src/opcode.rs

@@ -22,6 +22,7 @@
 pub enum Opcode {
  NOP,
  LDRI8(Dest8Bit),
+ LdR8HLAddr,
  Unimplemented(u8),
 }
 
@@ -39,7 +40,11 @@ impl Opcode {
  (0b00000000, 0b00000110) => {
  let reg_num = (data & 0b00111000) >> 3;
  let register = Dest8Bit::from_u8(reg_num);
- Opcode::LDRI8(register)
+ if register == Dest8Bit::HLAddr {
+ Opcode::LdR8HLAddr
+ } else {
+ Opcode::LDRI8(register)
+ }
  }
  _ => Opcode::Unimplemented(data),
  }
@@ -125,6 +130,12 @@ mod tests {
  assert_eq!(opcode, Opcode::LDRI8(destination));
  }
 
+ #[test]
+ fn should_return_ld_r8_addr_hl_given_00110110() {
+ let opcode = Opcode::decode(0b00110110);
+ assert_eq!(opcode, Opcode::LdR8HLAddr);
+ }
+
  #[test]
  fn should_return_b_when_given_0() {
  let register = Dest8Bit::from_u8(0);