From 412ae3726b0e1882f2af5f3728e348b752582ef6 Mon Sep 17 00:00:00 2001
From: OBattler <oubattler@gmail.com>
Date: Tue, 2 Jan 2018 21:35:25 +0100
Subject: [PATCH] Implemented the OPTi 495 A20 state switch (register 0x27 bit
 7), fixes the A20 gate stuck error.

---
 src/machine/m_at_opti495.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/src/machine/m_at_opti495.c b/src/machine/m_at_opti495.c
index 2033f4153..e629ffb25 100644
--- a/src/machine/m_at_opti495.c
+++ b/src/machine/m_at_opti495.c
@@ -292,6 +292,12 @@ static void opti495_write(uint16_t addr, uint8_t val, void *p)
                                 else
                                         mem_set_mem_state(0xf0000, 0x10000, MEM_READ_EXTERNAL | MEM_WRITE_INTERNAL);
                         }
+			if (optireg == 0x27)
+			{
+				mem_a20_key = (val & 0x80) ? 0x00 : 0x02;
+				mem_a20_recalc();
+				flushmmucache();
+			}
                 }
                 break;
         }