From b1e7fde1a31c26495820226da7a8ad0083f7ff37 Mon Sep 17 00:00:00 2001
From: Paul Mathieu <paul@ponteilla.net>
Date: Wed, 1 Oct 2025 23:33:18 +0200
Subject: [PATCH] polmon: now with ctrl+break!

---
 polmon.cc | 42 +++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 41 insertions(+), 1 deletion(-)

diff --git a/polmon.cc b/polmon.cc
index 2f18441..3bc55bf 100644
--- a/polmon.cc
+++ b/polmon.cc
@@ -1,5 +1,6 @@
 #include <cstdint>
 #include <cstdio>
+#include <cstring>
 
 #ifndef WOZMON
 #define WOZMON 0
@@ -13,6 +14,7 @@
 #define SHOWTITLE 0
 #define BOOTSTRAP 0
 #define LAUNCH 0
+#define CTRLBREAK 0
 #endif  // WOZMON
 
 #ifndef BACKSPACE
@@ -43,6 +45,10 @@
 #define LAUNCH 1
 #endif
 
+#ifndef CTRLBREAK
+#define CTRLBREAK 1
+#endif
+
 namespace {
 
 #if WOZMON
@@ -234,6 +240,35 @@ void LaunchFile(const char* name) {
                  : "ax", "memory");
 }
 
+#if CTRLBREAK
+
+constexpr uint16_t kCtrlBreakVector = (0x1b * 4);
+
+extern "C" void cbreak();
+asm("   .section .text.cbreak   \n"
+    "cbreak:                \n"
+    "   xor %ax, %ax        \n"
+    "   mov %ds, %ax        \n"
+    "   cli                 \n"
+    "   mov %ss, %ax        \n"
+    "   mov $0x2000, %sp    \n"
+    "   sti                 \n"
+    "   pushf               \n"
+    "   push %ax            \n"
+    "   mov $0x1000, %ax    \n"
+    "   push %ax            \n"
+    "   mov $0x20, %al      \n"
+    "   out %al, $0x20      \n"
+    "   iret                \n");
+
+void InstallCtrlBreak() {
+    auto vec = reinterpret_cast<void (**)()>(kCtrlBreakVector);
+    vec[0] = cbreak;
+    vec[1] = 0;
+}
+
+#endif  // CTRLBREAK
+
 bool ParseCommand(const char* buf, uint16_t& cur_addr, uint16_t& cur_seg) {
     bool dump = true;
     for (const char* ptr = buf; *ptr;) {
@@ -372,7 +407,12 @@ void polmon() {
 
 }  // namespace
 
-int main() { polmon(); }
+int main() {
+#if CTRLBREAK
+    InstallCtrlBreak();
+#endif  // CTRLBREAK
+    polmon();
+}
 
 #if BOOTSTRAP
 __attribute__((section(".init"), noreturn, used)) void _start() {