From 1f9f0a0d6e3703ff111395d8210e1001466debf4 Mon Sep 17 00:00:00 2001
From: OBattler <oubattler@gmail.com>
Date: Sat, 12 Apr 2025 14:54:35 +0200
Subject: [PATCH] NEAT: The chipset has its own A20 toggle, it cannot alter the
 external one as that's an input to the chipset, fixes #5332.

---
 src/chipset/neat.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/src/chipset/neat.c b/src/chipset/neat.c
index 1146ecbff..0661f89ee 100644
--- a/src/chipset/neat.c
+++ b/src/chipset/neat.c
@@ -956,8 +956,9 @@ neat_write(uint16_t port, uint8_t val, void *priv)
                                  dev->ems_size);
                     }
 
-                    mem_a20_key = !(val & RB12_GA20);
+                    mem_a20_alt = !(val & RB12_GA20);
                     mem_a20_recalc();
+                    flushmmucache();
                     break;
 
                 default:
@@ -987,7 +988,7 @@ neat_read(uint16_t port, void *priv)
             if ((dev->indx >= 0x60) && (dev->indx <= 0x6e))
                 ret = dev->regs[dev->indx];
             else if (dev->indx == 0x6f)
-                ret = (dev->regs[dev->indx] & 0xfd) | (mem_a20_key & 2);
+                ret = (dev->regs[dev->indx] & 0xfd) | ~(mem_a20_alt & 0x02);
             break;
 
         default: