bit 14 unset (w/ 15 set) = illegal ins

2 files changed, 8 insertions, 0 deletions

diff --git a/nandgame/assembler/disas.cpp b/nandgame/assembler/disas.cpp
index 8f6ff3b..ac7ca0c 100644
--- a/nandgame/assembler/disas.cpp
+++ b/nandgame/assembler/disas.cpp
@@ -171,6 +171,10 @@ static Decoded fixup_ins(uint16_t ins) {
 }
 
 std::string print_decoded(uint16_t ins, bool simplify) {
+    // illegal instruction
+    if ((ins & 0xC000) == 0x8000)
+        return "halt";
+
     Decoded d = simplify ? fixup_ins(ins) : decode_instruction(ins);
 
     std::string jumpdest_str = d.jumpdest.empty() ? "" : "." + d.jumpdest;
diff --git a/nandgame/assembler/disas.py b/nandgame/assembler/disas.py
index 56b44c4..5d8ccf5 100755
--- a/nandgame/assembler/disas.py
+++ b/nandgame/assembler/disas.py
@@ -183,6 +183,10 @@ def fixup_ins(ins: int) -> list[str]:
 
 
 def print_decoded(ins: int, simplify: bool) -> str:
+    # illegal instruction
+    if ins & 0xC000 == 0x8000:
+        return "halt"
+
     if simplify:
         (mnemonic, dest, op1, op2, jumpdest) = fixup_ins(ins)
     else: