Writing (debug output) to screen

src/kernel/boot/debug.c

@@ -2,6 +2,7 @@
 #include <stdarg.h>
 #include <stdint.h>
 #include <serial.h>
+#include <vga.h>
 
 // TODO: Temporary declarations
 void vga_write(char c);

src/kernel/boot/kmain.c

@@ -1,36 +1,13 @@
 #include <memory.h>
 #include <serial.h>
+#include <vga.h>
 #include <debug.h>
 
-void clear_screen()
-{
-  unsigned char *vidmem = P2V(0xB8000);
-  for(int i=0; i < 80*24*2; i++)
-    *vidmem++ = 0;
-}
-
-void print_string(char *str)
-{
-  unsigned char *vidmem = P2V(0xB8000);
-  while(*str)
-  {
-    *vidmem++ = *str++;
-    *vidmem++ = 0x7;
-  }
-}
-
-void vga_write(char c)
-{
-// TODO: DUMMY
-  (void)c;
-}
-
 void kmain()
 {
-  clear_screen();
-  print_string("Hello from c, world!");
-
   serial_init(PORT_COM1);
+  vga_init();
+
   debug_printf("Hello from debug printing function!\n");
   debug_printf("A number:%d\n", 12345);
   for(;;);

src/kernel/drivers/vga.c

@@ -0,0 +1,37 @@
+#include <vga.h>
+#include <memory.h>
+
+void *vidmem;
+struct {
+  uint8_t character;
+  uint8_t format;
+}__attribute__((packed)) buffer[VGA_SIZE];
+
+uint64_t cursor;
+
+void vga_init()
+{
+  vidmem = VGA_MEMORY;
+  memset(vidmem, 0, VGA_SIZE*2);
+}
+
+void flush()
+{
+  memcpy(vidmem, buffer, sizeof(buffer));
+}
+
+void vga_write(char c)
+{
+  switch(c)
+  {
+    case '\n':
+      cursor += VGA_COLS;
+      cursor -= VGA_COL(cursor);
+      break;
+    default:
+      buffer[cursor].character = c;
+      buffer[cursor].format = 0x7;
+      cursor++;
+  }
+  flush();
+}

src/kernel/drivers/vga.tt

@@ -0,0 +1,79 @@
+// vim: ft=c
+#include <ttest.h>
+
+#include <vga.h>
+#undef VGA_MEMORY
+#define VGA_MEMORY calloc(80*24,3)
+#include "vga.c"
+
+#include <stdint.h>
+
+struct cell
+{
+  uint8_t c;
+  uint8_t f;
+}__attribute__((packed));
+
+struct cell *cells;
+
+BEFORE()
+{
+  vga_init();
+  cells = vidmem;
+  cells[VGA_COLS*VGA_ROWS].c = '$';
+}
+
+#define VGA_ASSERT_EQ(pos, ch) ASSERT_EQ_CHR(cells[(pos)].c, (ch))
+
+
+TEST(vga_starts_with_a_clear_screen)
+{
+  VGA_ASSERT_EQ(VGA_COLS*VGA_ROWS-1, '\0');
+}
+
+TEST(vga_write_adds_character_to_vidmem)
+{
+  vga_write('a');
+  VGA_ASSERT_EQ(0, 'a');
+}
+
+TEST(vga_output_is_visible)
+{
+  vga_write('a');
+  ASSERT_NEQ_INT(cells[0].f, 0);
+}
+
+TEST(vga_write_adds_multiple_characters_to_vidmem)
+{
+  vga_write('a');
+  vga_write('b');
+  VGA_ASSERT_EQ(1, 'b');
+}
+
+TEST(vga_writes_entire_screen_full)
+{
+  for(int i = 0; i < VGA_COLS*VGA_ROWS; i++)
+    vga_write('x');
+
+  VGA_ASSERT_EQ(VGA_POS(VGA_ROWS-1, VGA_COLS-1), 'x');
+}
+TEST(vga_does_not_overflow_memory_area)
+{
+  for(int i = 0; i < (VGA_COLS*VGA_ROWS+1); i++)
+    vga_write('x');
+  VGA_ASSERT_EQ(VGA_COLS*VGA_ROWS, '$');
+}
+
+TEST(newline_moves_down_one_line_when_at_beginning)
+{
+  vga_write('\n');
+  vga_write('a');
+  VGA_ASSERT_EQ(VGA_POS(1,0), 'a');
+}
+TEST(newline_moves_to_beginning_of_line)
+{
+  vga_write('a');
+  vga_write('\n');
+  vga_write('b');
+  VGA_ASSERT_EQ(VGA_POS(1,0), 'b');
+}

src/kernel/include/vga.h

@@ -0,0 +1,14 @@
+#pragma once
+
+#define VGA_COLS 80
+#define VGA_ROWS 24
+#define VGA_SIZE (VGA_COLS*VGA_ROWS)
+
+#define VGA_ROW(pos) ((pos)/VGA_COLS)
+#define VGA_COL(pos) ((pos)%VGA_COLS)
+#define VGA_POS(row, col) ((row)*VGA_COLS + (col))
+
+#define VGA_MEMORY P2V(0xB8000)
+
+void vga_init();
+void vga_write(char c);