headless: $ED opcode = clean power-off (exit + battery save)

The unused SM83 opcode $ED now sets gb->poweroff, which breaks the headless
loop so the normal cart_free()->cart_save() path runs. Lets a guest OS shut the
emulator down cleanly (and flush its .sav) instead of relying on an external
timeout/SIGTERM, which could SIGKILL before the save. run_frame() also stops on
poweroff so exit is immediate.

1 files changed, 1 insertions, 0 deletions

diff --git a/src/gb.h b/src/gb.h
index 7218648..7959e60 100644
--- a/src/gb.h
+++ b/src/gb.h
@@ -116,6 +116,7 @@ struct GB {
     bool serial_log;   // print serial output to stderr (blargg tests)
     int  serial_out_fd; // if >=0, transmitted serial bytes written here (stdout)
     int  serial_in_fd;  // if >=0, received serial bytes read here (stdin), else 0xFF
+    bool poweroff;      // set by the $ED opcode: request a clean emulator exit
 };
 
 void gb_init(GB *gb);