Revert "Delete kernel.c"

This reverts commit 2dc94f58

minimalOS/kernel.c

+/*
+ * Desc: Minimal OS, to show how to boot an x86 machine. UFCFWK-15-2
+ */
+#if !defined(__cplusplus)
+#include <stdbool.h> /* C doesn't have booleans by default. */
+#endif
+#include <stddef.h>
+#include <stdint.h>
+ 
+/* Check if the compiler thinks we are targeting the wrong operating system. */
+#if defined(__linux__)
+#error "You are not using a cross-compiler, you will most certainly run into trouble"
+#endif
+ 
+/* This tutorial will only work for the 32-bit ix86 targets. */
+#if !defined(__i386__)
+#error "This tutorial needs to be compiled with a ix86-elf compiler"
+#endif
+ 
+/* Hardware text mode color constants. */
+enum vga_color {
+	COLOR_BLACK = 0,
+	COLOR_BLUE = 1,
+	COLOR_GREEN = 2,
+	COLOR_CYAN = 3,
+	COLOR_RED = 4,
+	COLOR_MAGENTA = 5,
+	COLOR_BROWN = 6,
+	COLOR_LIGHT_GREY = 7,
+	COLOR_DARK_GREY = 8,
+	COLOR_LIGHT_BLUE = 9,
+	COLOR_LIGHT_GREEN = 10,
+	COLOR_LIGHT_CYAN = 11,
+	COLOR_LIGHT_RED = 12,
+	COLOR_LIGHT_MAGENTA = 13,
+	COLOR_LIGHT_BROWN = 14,
+	COLOR_WHITE = 15,
+};
+ 
+uint8_t make_color(enum vga_color fg, enum vga_color bg) {
+  return fg | bg << 4;
+}
+ 
+uint16_t make_vgaentry(char c, uint8_t color) {
+  uint16_t c16 = c;
+  uint16_t color16 = color;
+  return c16 | color16 << 8;
+}
+ 
+size_t strlen(const char* str) {
+  size_t ret = 0;
+  while ( str[ret] != 0 )
+    ret++;
+  return ret;
+}
+
+static const size_t VGA_WIDTH = 80;
+static const size_t VGA_HEIGHT = 25;
+
+size_t terminal_row;
+size_t terminal_column;
+uint8_t terminal_color;
+uint16_t* terminal_buffer;
+ 
+void terminal_initialize() {
+  terminal_row = 0;
+  terminal_column = 0;
+  terminal_color = make_color(COLOR_LIGHT_GREY, COLOR_BLACK);
+  terminal_buffer = (uint16_t*) 0xB8000;
+  for (size_t y = 0; y < VGA_HEIGHT; y++) {
+    for (size_t x = 0; x < VGA_WIDTH; x++) {
+      const size_t index = y * VGA_WIDTH + x;
+      terminal_buffer[index] = make_vgaentry(' ', terminal_color);
+    }
+  }
+}
+ 
+void terminal_setcolor(uint8_t color) {
+  terminal_color = color;
+}
+ 
+void terminal_putentryat(char c, uint8_t color, size_t x, size_t y) {
+  const size_t index = y * VGA_WIDTH + x;
+  terminal_buffer[index] = make_vgaentry(c, color);
+}
+
+void terminal_putchar(char c) {
+  terminal_putentryat(c, terminal_color, terminal_column, terminal_row);
+  if (++terminal_column == VGA_WIDTH) {
+    terminal_column = 0;
+    if (++terminal_row == VGA_HEIGHT) {
+      terminal_row = 0;
+    }
+  }
+}
+ 
+void terminal_writestring(const char* data) {
+  size_t datalen = strlen(data);
+  for (size_t i = 0; i < datalen; i++)
+    terminal_putchar(data[i]);
+}
+
+#if defined(__cplusplus)
+extern "C" /* Use C linkage for kernel_main. */
+#endif
+void kernel_main() {
+  /* Initialize terminal interface */
+  terminal_initialize();
+  
+  /* Since there is no support for newlines in terminal_putchar
+   * yet, '\n' will produce some VGA specific character instead.
+   * This is normal.
+   */
+  terminal_writestring("Hello, kernel World!\n");
+}