implement TRAP

trap routines not yet implemented

src/vm/instruction.rs

@@ -84,7 +84,7 @@ pub fn execute_instruction(vm: &mut VM, instr: u16) {
         OpCode::JMP => no_op(vm, instr),
         OpCode::RES => no_op(vm, instr),
         OpCode::LEA => op_lea(vm, instr),
-        OpCode::TRAP => no_op(vm, instr),
+        OpCode::TRAP => op_trap(vm, instr),
         OpCode::NOOP => no_op(vm, instr),
     }
 }
@@ -105,3 +105,20 @@ fn op_lea(vm: &mut VM, instr: u16) {
     let offset = sign_extend(instr & 0xff, 9);
     vm.registers.set_reg(dr, vm.registers.pc + offset);
 }
+
+fn op_trap(vm: &mut VM, instr: u16) {
+    // conform to spec
+    // (we don't actually need it in this implementation)
+    vm.registers.r7 = vm.registers.pc;
+
+    let trap_vector = instr & 0xff;
+    match trap_vector {
+        0x20 => todo!("GETC"),
+        0x21 => todo!("OUT"),
+        0x22 => todo!("PUTS"),
+        0x23 => todo!("IN"),
+        0x24 => todo!("PUTSP"),
+        0x25 => todo!("HALT"),
+        _ => unimplemented!(),
+    }
+}

src/vm/mod.rs

@@ -192,6 +192,9 @@ impl VM {
         while running {
             let instr = self.mem.get_mem(self.registers.pc);
 
+            // NOTE
+            // remember PC points to the *next* instruction at all times
+
             // disallow reading past memory bounds
             if self.registers.pc as usize == MEM_SIZE - 1 {
                 running = false