void VGA_text(int x, int y, char * text_ptr) {
	int offset;
	volatile char * character_buffer =
			(char *) VGA_CHAR_BUFFER_AVALON_CHAR_BUFFER_SLAVE_BASE;	// VGA character buffer

	/* assume that the text string fits on one line */
	offset = (y << 7) + x;
	while (*(text_ptr)) {
		*(character_buffer + offset) = *(text_ptr);	// write to the character buffer
		++text_ptr;
		++offset;
	}
}

/****************************************************************************************
 * Draw a filled rectangle on the VGA monitor
 ****************************************************************************************/
void VGA_box(int x1, int y1, int x2, int y2, short pixel_color) {
	int pixel_ptr, row, col;

	/* assume that the box coordinates are valid */
	for (row = y1; row <= y2; row++)
		for (col = x1; col <= x2; ++col) {
			pixel_ptr = VGA_PIXEL_DMA_BASE	+ (row << 10) + (col << 1);
			*(short *) pixel_ptr = pixel_color;		// set pixel color