From c36bdc22f66fbc58c82d4e3812e0110e50ece208 Mon Sep 17 00:00:00 2001
From: Lior Halphon <LIJI32@gmail.com>
Date: Sat, 14 Nov 2020 13:55:39 +0200
Subject: [PATCH] More accurate interrupt emulation

---
 Core/sm83_cpu.c | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/Core/sm83_cpu.c b/Core/sm83_cpu.c
index 3b3eceb..ffc5997 100644
--- a/Core/sm83_cpu.c
+++ b/Core/sm83_cpu.c
@@ -261,7 +261,20 @@ static void cycle_oam_bug(GB_gameboy_t *gb, uint8_t register_id)
     }
     GB_trigger_oam_bug(gb, gb->registers[register_id]); /* Todo: test T-cycle timing */
     gb->pending_cycles = 4;
+}
 
+static void cycle_oam_bug_pc(GB_gameboy_t *gb)
+{
+    if (GB_is_cgb(gb)) {
+        /* Slight optimization */
+        gb->pending_cycles += 4;
+        return;
+    }
+    if (gb->pending_cycles) {
+        GB_advance_cycles(gb, gb->pending_cycles);
+    }
+    GB_trigger_oam_bug(gb, gb->pc); /* Todo: test T-cycle timing */
+    gb->pending_cycles = 4;
 }
 
 static void flush_pending_cycles(GB_gameboy_t *gb)
@@ -1538,8 +1551,9 @@ void GB_cpu_run(GB_gameboy_t *gb)
         gb->halted = false;
         uint16_t call_addr = gb->pc;
         
-        cycle_no_access(gb);
-        cycle_no_access(gb);
+        gb->last_opcode_read = cycle_read_inc_oam_bug(gb, gb->pc++);
+        cycle_oam_bug_pc(gb);
+        gb->pc--;
         GB_trigger_oam_bug(gb, gb->registers[GB_REGISTER_SP]); /* Todo: test T-cycle timing */
         cycle_no_access(gb);