Update for publishing

.gitignore

@@ -2,3 +2,5 @@
 *.err
 *.exe
 .ccls-cache/
+ccls.log
+capture/

README.md

@@ -1,7 +1,47 @@
-# VGA logic units in 256 colors and SVGA mode usage
+# VGA and SVGA code examples
 
 Some code to exercise the four logic units of the VGA card in
 256 color mode, as well as code that gets SVGA mode
 working. Most of this is in C, but some of it's in assembler
 to help me learn assembler better, as well as get comfortable with
 C/asm interop on x86.
+
+Check out the video I wrote all this code to support:
+https://makertube.net/w/sQSZJcxh8CRuMZWVh8Q6aF
+
+Read more about my project The Industrious Rabbit at
+https://theindustriousrabbit.com/
+
+## Building
+
+You'll need [Open Watcom 2.0](https://open-watcom.github.io/). You can use
+`wmake` on the `makefile` to build some of these, and
+`wcl386 -q -bt=dos -l=dos4g <c or asm files>` for the others. All of these
+run in 32-bit protected mode within a DPMI wrapper and in a flat memory space,
+because I *really don't* want to deal with segment:offset addressing.
+
+## What's here
+
+### `main.c` and `vga.asm`
+
+C code that exercises a bunch of the VGA registers by transforming a colored
+cube of all 256 VGA colors in different ways. The display is set to unchained
+mode. Lots of latch copies and trasnforming data with stuff in the latches.
+The core of the transformation code is in `vga.asm`, which is also where the
+keyboard handler for exiting the program lives.
+
+### `svga.c`, `vesa.c`, `dpmi.c`, and `bmp.c`
+
+Display a bitmap in a 640x480x256 SVGA mode. Trying to find a fully working
+SVGA, DOS Protected Mode Interface, and VESA example was tough, so hopefully
+this will help you out if you're trying to do the same thing!
+
+### `simple.c` and `asmvga.asm`
+
+These both draw a single dot on the screen, but in different ways:
+
+* `simple.c` draws the dot directly to VGA memory
+* `asmvga.asm` allocates a block of RAM, writes the pixel there, then
+  shovels the data from the RAM into the VGA card with `rep movsb`, which
+  is the procedure a game would use to draw to a non-VGA RAM buffer and then
+  copy when done.

asmvga.asm

@@ -0,0 +1,75 @@
+.386
+.model flat,c
+.STACK 100h
+
+.data
+bufferPtr dword 0
+bufferHandleLow word 0
+bufferHandleHigh word 0
+
+.code
+
+main PROC
+  ; we need es the same as ds for movsb
+  mov ax,ds
+  mov es,ax
+
+  ; place to catch bpint
+  mov cx,0fh
+  mov dx,1
+  mov ah,86h
+  int 15h
+
+  ; reserve ram
+  mov ax,0501h
+  mov bx,0
+  mov cx,64000
+  int 31h
+  shl ebx,16
+  mov bx,cx
+  mov bufferPtr,ebx
+  mov bufferHandleLow,di
+  mov bufferHandleHigh,si
+
+  ; clear ram
+  mov ecx,64000
+  mov edi,ebx
+  mov al,0
+  rep stosb
+
+  ; write pixel 15 at (10,10)
+  mov edi,ebx
+  add edi,320*10+10
+  mov al,15
+  stosb
+
+  ; switch to 320x200 256 color chunky chained mode
+  mov ah,0h
+  mov al,13h
+  int 10h
+
+  ; copy buffer to vga card
+  mov esi,bufferPtr
+  mov edi,0a0000h
+  mov ecx,320*200
+  rep movsb
+
+  ; wait 5s
+  mov cx,0fh
+  mov dx,5000
+  mov ah,86h
+  int 15h
+
+  ; free memory
+  mov ax,0502h
+  mov si,bufferHandleHigh
+  mov di,bufferHandleLow
+  int 31h
+
+  ; terminate with return code
+  mov ah,4Ch
+  mov al,00h
+  int 21h
+main ENDP
+
+END main

main.c

@@ -47,7 +47,14 @@ void populateExampleCube(void) {
   }
 }
 
+void forceReadVGA(char far *vga);
+#pragma aux forceReadVGA = \
+"mov bl,BYTE PTR [eax]" \
+parm [ eax ] \
+modify [ bl ];
+
 int main(void) {
+  char a;
   // activate unchained vga mode
   // place some data into video memory to be latch copied
   // show off the following
@@ -93,11 +100,50 @@ int main(void) {
   writeCube(10, 0x00, 0, 3);
   writeCube(15, 0x00, 3, 0);
 
+  outpw(0x3ce, 0x0000);
+  outpw(0x3ce, 0x0001);
+  outpw(0x3ce, 0x0002);
+  outpw(0x3ce, 0x0003);
+  /*
+  outpw(0x3ce, 0x0005);
+  */
+  outpw(0x3ce, 0xff08);
+  outpw(0x3c4, 0x0f02);
+  /*
+  outp(0x3ce, 0x08);
+  outp(0x3cf, 0xff);
+  */
+
+  VGA[0] = 255;
+  // read the above. if you're reading the value and doing nothing with it, watcom will optimize it out
+  forceReadVGA(VGA);
+
+  //outp(0x3cf, 0xff);
+  // all from latches
+  outpw(0x3ce, 0x0008);
+
+  VGA[2] = 127;
+
+  // all but the first bit from incoming data
+  outpw(0x3ce, 0xfe08);
+
+  VGA[4] = 2;
+
+  a = VGA[4];
+
+  /*
+  outp(0x3cf, 0x00);
+
+  VGA[410] = 0;
+  */
+
   while (keyboardPressed == 0);
 
   _dos_setvect(9, int9Save);
 
   enableTextMode();
 
+  printf("%d\n", a);
+
   return 0;
 }

simple.c

@@ -0,0 +1,23 @@
+#include <i86.h>
+#include <dos.h>
+#include <conio.h>
+
+int main(void) {
+  union REGS regs;
+
+  regs.w.ax = 0x13;
+
+  int386(0x10, &regs, &regs);
+
+  delay(5000);
+
+  *((unsigned char far *)0xa0000 + (320 * 10) + 10) = 15;
+
+  delay(2000);
+
+  regs.w.ax = 0x03;
+
+  int386(0x10, &regs, &regs);
+
+  return 0;
+}