From 7cd0eb4a4ba06e073470dc039e2553cd0d32a04f Mon Sep 17 00:00:00 2001
From: ekeeke31 <ekeeke31@fcb46045-4337-0410-a722-cd382f7ce8f6>
Date: Thu, 28 Apr 2011 00:13:23 +0000
Subject: [PATCH] improved HINT accuracy in Master System Compatibility mode.

---
 source/system.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/source/system.c b/source/system.c
index a36f406..5753c0c 100644
--- a/source/system.c
+++ b/source/system.c
@@ -757,6 +757,14 @@ static void system_frame_sms(int do_skip)
       hint_pending = 0x10;
       if (reg[0] & 0x10)
       {
+        /* IRQ line is latched between instructions, on instruction last cycle          */
+        /* This means that if Z80 cycle count is exactly a multiple of MCYCLES_PER_LINE, */
+        /* interrupt should be triggered AFTER the next instruction.                    */
+        if ((mcycles_z80 % MCYCLES_PER_LINE) == 0)
+        {
+          z80_run(mcycles_z80 + 1);
+        }
+
         Z80.irq_state = ASSERT_LINE;
       }
     }