For slower display controllers used on fast processors, the use of port-lines may be
the only solution. This method of accessing the display has the disadvantage of being
somewhat slower than direct bus-interface but, particularly with a cache that minimizes
the accesses to the display, the display update is not slowed down significantly.
All that needs to be done is to define routines or macros which set or read the hardware
ports/buffers that the display is connected to. This type of interface is also supported
by different drivers for the different display controllers.