From cada868428f2eb74a973f2188bf31cd5dc3ebfad Mon Sep 17 00:00:00 2001
From: SarahW <pcem@pcem-emulator.co.uk>
Date: Sat, 21 Nov 2020 20:45:56 +0000
Subject: [PATCH] Tweak accesses to S3 system control and extension registers.
 Fixes banking on some versions of UNIVBE (eg as used by Pro Pinball : The
 Web).

---
 src/vid_s3.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/src/vid_s3.c b/src/vid_s3.c
index f4064a9..f56ae34 100644
--- a/src/vid_s3.c
+++ b/src/vid_s3.c
@@ -999,7 +999,11 @@ void s3_out(uint16_t addr, uint8_t val, void *p)
                         return;
                 if ((svga->crtcreg == 7) && (svga->crtc[0x11] & 0x80))
                         val = (svga->crtc[7] & ~0x10) | (val & 0x10);
-                if (svga->crtcreg >= 0x20 && svga->crtcreg != 0x38 && (svga->crtc[0x38] & 0xcc) != 0x48) return;
+                if (svga->crtcreg >= 0x20 && svga->crtcreg != 0x38 && svga->crtcreg != 0x39 && (svga->crtc[0x38] & 0xcc) != 0x48)
+                {
+                        if (!((svga->crtc[0x39] & 0xe0) == 0xa0 && svga->crtcreg >= 0x40 && svga->crtcreg <= 0x6d))
+                                return;
+                }
                 old = svga->crtc[svga->crtcreg];
                 svga->crtc[svga->crtcreg] = val;
                 switch (svga->crtcreg)