From c5e314048afd1ba3f87204b0655af70f95ae7ab1 Mon Sep 17 00:00:00 2001
From: "Juan J. Martinez" <jjm@usebox.net>
Date: Thu, 8 Jun 2023 21:49:39 +0100
Subject: Set VGA 320x200 256 col at 60Hz

---
 TODO.md   |  3 +--
 src/vga.c | 28 ++++++++++++++++++++++++++++
 2 files changed, 29 insertions(+), 2 deletions(-)

diff --git a/TODO.md b/TODO.md
index 090b178..a3e7d49 100644
--- a/TODO.md
+++ b/TODO.md
@@ -1,6 +1,7 @@
 # TODO
 
 - drawing
+  - detect VGA
   - sw blitter
 - input
   - joystick?
@@ -19,6 +20,4 @@
 
 # REVIEW
 
-- review use of the timer
-    - tick frequency is 18.2 times per second
 - use dosemu instead of dosbox?
diff --git a/src/vga.c b/src/vga.c
index 6665c79..e90ebba 100644
--- a/src/vga.c
+++ b/src/vga.c
@@ -4,6 +4,7 @@
 #include <dpmi.h>
 #include <sys/nearptr.h>
 #include <pc.h>
+#include <dos.h>
 
 #include "vga.h"
 
@@ -29,6 +30,33 @@ void set_mode(uint8_t mode)
     __dpmi_regs regs = { 0 };
     regs.x.ax = mode;
     __dpmi_int(0x10, &regs);
+
+    if (mode == 0x13)
+    {
+        /* setup the VGA: 320x200 @ 60Hz */
+        /* from: https://gist.github.com/juj/34306e6da02a8a7043e393f01e013f24 */
+        disable();
+
+        /* XXX: probably not neeed */
+        wait_vsync();
+
+        outportw(0x3d4, 0x0011); /* Turn off write protect to CRTC registers */
+        outportw(0x3d4, 0x0b06); /* New vertical total=525 lines, bits 0-7 */
+        outportw(0x3d4, 0x3e07); /* New vertical total=525 lines, bits 8-9 */
+
+        outportw(0x3d4, 0xb910); /* Vsync start=scanline 185 */
+        outportw(0x3d4, 0x8f12); /* Vertical display end=scanline 399, bits 0-7 */
+        outportw(0x3d4, 0xb815); /* Vertical blanking start=scanline 440, bits 0-7 */
+        outportw(0x3d4, 0xe216); /* Adjust vblank end position */
+        outportw(0x3d4, 0x8511); /* Vsync length=2 lines + turn write protect back on */
+
+        /* XXX: probably not neeed */
+        wait_vsync();
+
+        outportw(0x3d4, 0x2813); /* 8 pixel chars */
+        outportw(0x3d4, 0x8e11); /* restore retrace */
+        enable();
+    }
 }
 
 void wait_vsync()
-- 
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