lesson 15, video ports

15-video-ports/kernel/kernel.c

@@ -0,0 +1,32 @@
+#include "../drivers/ports.h"
+
+void main() {
+    /* Screen cursor position: ask VGA control register (0x3d4) for bytes
+     * 14 = high byte of cursor and 15 = low byte of cursor. */
+    port_byte_out(0x3d4, 14); /* Requesting byte 14: high byte of cursor pos */
+    /* Data is returned in VGA data register (0x3d5) */
+    int position = port_byte_in(0x3d5);
+    position = position << 8; /* high byte */
+
+    port_byte_out(0x3d4, 15); /* requesting low byte */
+    position += port_byte_in(0x3d5);
+
+    /* VGA 'cells' consist of the character and its control data
+     * e.g. 'white on black background', 'red text on white bg', etc */
+    int offset_from_vga = position * 2;
+
+    /* Now you can examine both variables using gdb, since we still
+     * don't know how to print strings on screen. Run 'make debug' and
+     * on the gdb console:
+     * breakpoint kernel.c:21
+     * continue
+     * print position
+     * print offset_from_vga
+     */
+
+    /* Let's write on the current cursor position, we already know how
+     * to do that */
+    char *vga = 0xb8000;
+    vga[offset_from_vga] = 'X'; 
+    vga[offset_from_vga+1] = 0x0f; /* White text on black background */
+}