Drain keyboard buffer after running program

Sometimes when a program exits stray keystrokes are left in the keyboard
buffer, and the menu then responds to them (e.g. by launching the first
menu item). For example, one of the games crashes (due to unrelated
reasons) and then the first game on the menu automatically launches, and
Blake gets upset. This won't stop the crash but will hopefully stop the
first game from launching when it does.

Author: skissane

dosmenu.c

@@ -295,6 +295,25 @@ int countSections(struct section *sections) {
         return i;
 }
 
+// Check if a key is pending.
+// Key is pending if head and tail pointers of keyboard buffer in
+// BIOS data area (BDA) are different.
+int keyPending() {
+	int head, tail;
+	disable();
+	head = peek(0x40,0x1A); // 40:1A = keybuf head pointer
+	tail = peek(0x40,0x1C); // 40:1C = keybuf tail pointer
+	enable();
+	return head != tail;
+}
+
+// Ignore all pending keys
+// This helps consume any stray keys after exiting
+void drainInput() {
+	while (keyPending())
+		readScanCode();
+}
+
 int main(int argc, char**argv) {
         struct section *sections;
         char *title, *saveCWD, *borderColorName;
@@ -366,6 +385,7 @@ int main(int argc, char**argv) {
                         chdir(saveCWD);
                         resetVideo();
                         _setcursortype(_NOCURSOR);
+			drainInput();
                 }
         }
 }