Stub 8-bit LD Instructions

src/cpu.rs

@@ -1,7 +1,50 @@
+use super::instructions::Instruction;
+
 // Gameboy CPU
 pub struct LR35902 {
     sp: u16,
     pc: u16,
+    reg: Registers,
+}
+
+impl LR35902 {
+    pub fn cycle(&mut self) {
+        let opcode = Self::fetch();
+        self.decode(opcode);
+        Self::execute();
+    }
+
+    fn fetch() -> u8 {
+        unimplemented!()
+    }
+
+    fn decode(&mut self, opcode: u8) {
+        // Source: https://gb-archive.github.io/salvage/decoding_gbz80_opcodes/Decoding%20Gamboy%20Z80%20Opcodes.html
+        // x = the opcode's 1st octal digit (i.e. bits 7-6)
+        // y = the opcode's 2nd octal digit (i.e. bits 5-3)
+        // z = the opcode's 3rd octal digit (i.e. bits 2-0)
+        // p = y rightshifted one position (i.e. bits 5-4)
+        // q = y modulo 2 (i.e. bit 3)
+
+        let x = opcode >> 6;
+        let y = (opcode & 0b00111000) >> 3; // 0b00111000 = 0x38
+        let z = opcode & 0b00000111; // 0b00000111 = 0x07
+        let p = y >> 1;
+        let q = y & 0b00000001; // 0b001 = 0x1;
+
+        let d: i8 = 0; // Displacement Byte
+        let n: u8 = 0; // 8-bit Immediate Operand
+        let nn: u16 = 0; // 16-bit Immediate Operand
+
+        match (x, z, q, y, p) {
+            (0, 0, _, 0, _) => Instruction::nop(),
+            _ => panic!("Unexpected Opcode!"),
+        }
+    }
+
+    fn execute() {
+        unimplemented!()
+    }
 }
 
 #[derive(Debug, Copy, Clone, Default)]