33 lines
1.2 KiB
C
Executable File
33 lines
1.2 KiB
C
Executable File
#include "../drivers/ports.h"
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void _start() {
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/* Screen cursor position: ask VGA control register (0x3d4) for bytes
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* 14 = high byte of cursor and 15 = low byte of cursor. */
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port_byte_out(0x3d4, 14); /* Requesting byte 14: high byte of cursor pos */
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/* Data is returned in VGA data register (0x3d5) */
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int position = port_byte_in(0x3d5);
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position = position << 8; /* high byte */
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port_byte_out(0x3d4, 15); /* requesting low byte */
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position += port_byte_in(0x3d5) + 250;
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/* VGA 'cells' consist of the character and its control data
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* e.g. 'white on black background', 'red text on white bg', etc */
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int offset_from_vga = position * 2;
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/* Now you can examine both variables using gdb, since we still
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* don't know how to print strings on screen. Run 'make debug' and
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* on the gdb console:
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* breakpoint kernel.c:21
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* continue
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* print position
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* print offset_from_vga
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*/
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/* Let's write on the current cursor position, we already know how
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* to do that */
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char *vga = (char *) 0xb8000;
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vga[offset_from_vga] = 'X';
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vga[offset_from_vga+1] = 0x0f; /* White text on black background */
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}
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