Make sure unsupported/illegal instructions are caught

src/core.rs

@@ -47,6 +47,8 @@ impl Core {
                 }
             };
 
+            assert_eq!(instr & 3, 3, "Compressed instructions not supported");
+
             let instr = Instruction(instr);
 
             let runner = find_runner(instr);
@@ -65,6 +67,9 @@ impl Core {
                         break;
                     }
                 }
+            } else {
+                eprintln!("Invalid Instruction");
+                break;
             }
         }
     }

src/decode.rs

@@ -12,7 +12,7 @@ impl Instruction {
 
     /// Returns the opcode of the instruction, with the last 2 bits stripped away, as they are always 0b11 in a non-compressed instruction
     pub fn opcode_noncompressed(&self) -> u8 {
-        debug_assert_eq!(self.0 & 0b11, 0b11);
+        debug_assert_eq!(self.0 & 0b11, 0b11, "Compressed (or invalid) opcode");
         (self.0 >> 2 & 0x1f) as u8
     }