From cdc7b2ae532fd3a93e13784812f7501f2fd5c07a Mon Sep 17 00:00:00 2001
From: Benji Dial <benji3.141@gmail.com>
Date: Sat, 14 Dec 2019 18:31:34 -0500
Subject: more of bootloader, tiny kernel stub

---
 src/kernel/vga.c | 71 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 71 insertions(+)
 create mode 100644 src/kernel/vga.c

(limited to 'src/kernel/vga.c')

diff --git a/src/kernel/vga.c b/src/kernel/vga.c
new file mode 100644
index 0000000..046dda7
--- /dev/null
+++ b/src/kernel/vga.c
@@ -0,0 +1,71 @@
+/*
+Copyright 2019 Benji Dial
+
+Permission to use, copy, modify, and/or distribute this
+software for any purpose with or without fee is hereby
+granted, provided that the above copyright notice and this
+permission notice appear in all copies.
+
+THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS
+ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL
+IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO
+EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER
+RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION,
+ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE
+OF THIS SOFTWARE.
+*/
+
+#include "vga.h"
+
+uint16_t cursor_pos = 0;
+uint8_t color = 0xf0;
+#define cols 80
+#define rows 25
+
+void scroll(void) {
+  cursor_pos -= cols * 2;
+  uint32_t *limit = (uint32_t *)(VGA_BUFFER + cols * (rows - 1));
+  for (uint32_t *i = (uint32_t *)VGA_BUFFER; i < limit; ++i)
+    *i = *(i + cols / 2);
+  limit += cols / 2;
+  uint32_t fill = (color * 0x0100 + (uint8_t)' ') * 0x00010001;
+  for (uint32_t *i = limit - cols / 2; i < limit; ++i)
+    *i = fill;
+}
+
+void put_char(uint8_t ch) {
+  switch (ch) {
+  case '\b':
+    if (cursor_pos)
+      VGA_BUFFER[cursor_pos -= 2] = (uint8_t)' ';
+    break;
+  case '\t':
+    while ((cursor_pos % (cols * 2)) % 20)
+      put_char(' ');
+    break;
+  case '\n':
+    if ((cursor_pos = (cursor_pos / (cols * 2) + 1) * (cols * 2)) >= cols * rows * 2)
+      scroll();
+    break;
+  default:
+    VGA_BUFFER[cursor_pos++] = ch;
+    VGA_BUFFER[cursor_pos++] = color;
+    if (cursor_pos == (cols * rows * 2))
+      scroll();
+  }
+}
+
+void put_sz(uint8_t *sz) {
+  while (*sz)
+    put_char(*(sz++));
+}
+
+void move_cursor(uint8_t col, uint8_t row) {
+  cursor_pos = (col + row * cols) * 2;
+}
+
+void set_color(uint8_t c) {
+  color = c;
+}
-- 
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