vga_get_atr
atr = vga_get_atr(VGA_REG_BASE, VGA_AC_MODE_CONTROL);
int vga_get_atr(int, int);
val = vga_get_atr(VGA_REG_BASE, VGA_AC_MODE_CONTROL);
reg[6] = vga_get_atr(VGA_REG_BASE, VGA_AC_MODE_CONTROL);