From 9b0d260d5decdfd43d050e55f21c38d284a7e4ac Mon Sep 17 00:00:00 2001
From: John Bintz <hello@theindustriousrabbit.com>
Date: Tue, 19 Mar 2024 22:08:42 -0400
Subject: [PATCH] assembler latch copying

---
 .gitignore |  1 +
 main.c     | 30 +++++++++++++++++-
 vga.asm    | 90 +++++++++++++++++++++++++++++++++++++++++++++++++++++-
 3 files changed, 119 insertions(+), 2 deletions(-)

diff --git a/.gitignore b/.gitignore
index 4b6b859..d16db97 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,3 +1,4 @@
 *.o
 *.err
 *.exe
+.ccls-cache/
diff --git a/main.c b/main.c
index f8e5b8f..58702b4 100644
--- a/main.c
+++ b/main.c
@@ -3,9 +3,26 @@
 
 extern void __cdecl enableUnchainedVGAMode();
 extern void __cdecl enableTextMode();
+extern void __cdecl fillScreen(int);
+extern void __cdecl latchCopyCube();
 
 char far *VGA = (char*)0xA0000;
 
+#define PLANE_WIDTH (320 / 4)
+
+void populateExampleCube(void) {
+  int y, x;
+
+  outp(0x3c4, 0x02);
+
+  for (y = 0; y < 15; ++y) {
+    for (x = 0; x < 15; ++x) {
+      outp(0x3c5, 1 << (x % 4));
+      VGA[y * PLANE_WIDTH + x / 4] = y * 16 + x;
+    }
+  }
+}
+
 int main(void) {
   // activate unchained vga mode
   // set up 8 very clear colors
@@ -19,6 +36,15 @@ int main(void) {
 
   enableUnchainedVGAMode();
 
+  fillScreen(0);
+
+  populateExampleCube();
+  latchCopyCube();
+
+  delay(2000);
+
+  /*
+
   outp(0x3c4, 0x02);
 
   for (i = 0; i < 200; ++i) {
@@ -28,7 +54,9 @@ int main(void) {
     }
   }
 
-  delay(5000);
+  */
+
+  //delay(3000);
 
   enableTextMode();
 }
diff --git a/vga.asm b/vga.asm
index 88c8ae7..cee73f5 100644
--- a/vga.asm
+++ b/vga.asm
@@ -1,13 +1,20 @@
 PUBLIC _enableUnchainedVGAMode
 PUBLIC _enableTextMode
+PUBLIC _fillScreen
+PUBLIC _latchCopyCube
 
 DISPLAY_MODE_VGA equ 13h
 DISPLAY_MODE_TEXT equ 03h
 
 VGA_SEQUENCE_CONTROLLER_INDEX equ 0x3c4
-VGA_SEQUENCE_CONTROLLER_DATA equ 0x3c5h
+VGA_SEQUENCE_CONTROLLER_DATA equ 0x3c5
 VGA_SEQUENCE_CONTROLLER_MEMORY_MODE equ 0x04
 
+VGA_SEQUENCE_CONTROLLER_MAP_MASK_MODE equ 0x02
+
+VGA_GRAPHICS_MODE_INDEX equ 0x3CE
+VGA_GRAPHICS_MODE equ 0x05
+
 VGA_CRT_CONTROLLER_INDEX equ 0x03d4
 VGA_CRT_CONTROLLER_DATA equ 0x03d5
 VGA_CRT_CONTROLLER_UNDERLINE_LOC equ 0x14
@@ -45,4 +52,85 @@ _enableTextMode:
   int 10h
   ret
 
+_fillScreen:
+  push ebp
+  mov ebp, esp
+
+  ; set all bitplanes
+  mov dx, VGA_SEQUENCE_CONTROLLER_INDEX
+  mov al, 0x02
+  mov ah, 0fh
+  out dx, ax
+
+  mov al, [ebp+8] ; requested color
+
+  mov cx, 16000 ; loop index
+  mov ebx, 0xa0000
+_fillScreen_loop:
+  mov BYTE PTR [ebx], al
+  inc ebx
+  loop _fillScreen_loop
+
+  mov esp,ebp
+  pop ebp
+
+  ret
+
+_latchCopyCube:
+  push ebp
+  mov ebp,esp
+  ; we need an x and y variable
+  sub esp,4 ; y
+
+  ; enable latch reads
+  mov dx, VGA_SEQUENCE_CONTROLLER_INDEX
+  mov al, VGA_SEQUENCE_CONTROLLER_MAP_MASK_MODE
+  mov ah, 0xf
+  out dx, ax
+
+  mov dx, VGA_GRAPHICS_MODE_INDEX
+  mov al, 0x08
+  mov ah, 0x00
+  out dx, ax
+
+  mov DWORD PTR [ebp-4],16
+  ; read across the cube, should take 4 * 16 reads
+  mov cx,[ebp-4]
+_latchCopyCube_yLoop:
+  mov [ebp-4],cx ; put y back in loop
+
+  mov eax,[ebp-4] ; put y in ax
+  dec eax ; offset by 1 for loop
+  ; can only multiply in ax
+  mov bl,80
+  mul bl ; number of lines
+  add eax,0xa0000 ; vga base address
+
+  ; start x loop
+  mov cx,4
+_latchCopyCube_xLoop:
+
+  ; fill latches
+  mov bl, BYTE PTR [eax]
+
+  ; write blank
+  mov [eax+12],0
+
+  ; increment vga pointer
+  inc eax
+
+  ; loop until x is 0
+  loop _latchCopyCube_xLoop
+
+  ; restore y for looping
+  mov cx,[ebp-4]
+
+  ; loop until y is 0
+  loop _latchCopyCube_yLoop
+
+  ; put things back
+  mov esp,ebp
+  pop ebp
+  ret
+
 end