From 09917053798839a251acbd91a4fb097d74aa2a30 Mon Sep 17 00:00:00 2001
From: Lior Halphon <LIJI32@gmail.com>
Date: Thu, 22 Sep 2016 01:51:09 +0300
Subject: [PATCH] Refined HALT bug behavior, fixed Robocop

---
 Core/gb.h      |  1 +
 Core/z80_cpu.c | 15 +++++++++------
 2 files changed, 10 insertions(+), 6 deletions(-)

diff --git a/Core/gb.h b/Core/gb.h
index b1326f8..e8d929f 100644
--- a/Core/gb.h
+++ b/Core/gb.h
@@ -226,6 +226,7 @@ typedef struct GB_gameboy_s {
         bool stopped;
         bool boot_rom_finished;
         bool ime_toggle; /* ei (and di in CGB) have delayed effects.*/
+        bool halt_bug;
 
         /* Misc state*/
         /* IR */
diff --git a/Core/z80_cpu.c b/Core/z80_cpu.c
index b664ace..c5a3528 100644
--- a/Core/z80_cpu.c
+++ b/Core/z80_cpu.c
@@ -684,6 +684,11 @@ static void halt(GB_gameboy_t *gb, uint8_t opcode)
 {
     GB_advance_cycles(gb, 4);
     gb->halted = true;
+    /* Despite what some online documentations say, the HALT bug also happens on a CGB, in both CGB and DMG modes. */
+    if (!gb->ime && (gb->interrupt_enable & gb->io_registers[GB_IO_IF] & 0x1F) != 0) {
+        gb->halted = false;
+        gb->halt_bug = true;
+    }
 }
 
 static void ret_cc(GB_gameboy_t *gb, uint8_t opcode)
@@ -1332,12 +1337,9 @@ static GB_opcode_t *opcodes[256] = {
 void GB_cpu_run(GB_gameboy_t *gb)
 {
     gb->vblank_just_occured = false;
-    bool interrupt = gb->interrupt_enable & gb->io_registers[GB_IO_IF];
-    bool halt_bug = false;
+    bool interrupt = gb->interrupt_enable & gb->io_registers[GB_IO_IF] & 0x1F;
 
     if (interrupt) {
-        /* Despite what some online documentations say, the HALT bug also happens on a CGB, in both CGB and DMG modes. */
-        halt_bug = gb->halted;
         gb->halted = false;
     }
 
@@ -1354,7 +1356,7 @@ void GB_cpu_run(GB_gameboy_t *gb)
 
     if (effecitve_ime && interrupt) {
         uint8_t interrupt_bit = 0;
-        uint8_t interrupt_queue = gb->interrupt_enable & gb->io_registers[GB_IO_IF];
+        uint8_t interrupt_queue = gb->interrupt_enable & gb->io_registers[GB_IO_IF] & 0x1F;
         while (!(interrupt_queue & 1)) {
             interrupt_queue >>= 1;
             interrupt_bit++;
@@ -1367,8 +1369,9 @@ void GB_cpu_run(GB_gameboy_t *gb)
     }
     else if(!gb->halted && !gb->stopped) {
         uint8_t opcode = GB_read_memory(gb, gb->pc++);
-        if (halt_bug) {
+        if (gb->halt_bug) {
             gb->pc--;
+            gb->halt_bug = false;
         }
         opcodes[opcode](gb, opcode);
     }