From 2efda3598b1521c5899f0a20d0b94fd97b2b4c6e Mon Sep 17 00:00:00 2001
From: SarahW <pcem@pcem-emulator.co.uk>
Date: Fri, 2 Oct 2020 17:21:41 +0100
Subject: [PATCH] Trident TVGA8900D appears to implement port 0x3db as an
 alternative clock select. Fixes pixel clocks & refresh rates on this card.

---
 src/vid_tvga.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/src/vid_tvga.c b/src/vid_tvga.c
index d9213ea..59e11e3 100644
--- a/src/vid_tvga.c
+++ b/src/vid_tvga.c
@@ -161,6 +161,16 @@ void tvga_out(uint16_t addr, uint8_t val, void *p)
                         tvga_recalcbanking(tvga);
                 }
                 return;
+                case 0x3DB:
+                if (tvga->id == TVGA_8900D)
+                {
+                        /*3db appears to be a 4 bit clock select register on 8900D*/
+                        svga->miscout = (svga->miscout & ~0x0c) | ((val & 3) << 2);
+                        tvga->newctrl2 = (tvga->newctrl2 & ~0x01) | ((val & 4) >> 2);
+                        tvga->oldctrl1 = (tvga->oldctrl1 & ~0x10) | ((val & 8) << 1);
+                        svga_recalctimings(svga);
+                }
+                break;
         }
         svga_out(addr, val, svga);
 }