- update(): skip screen update if the vertical retrace is in progress   (using 72 Hz vertical frequency). The vertial retrace phase is often used for   vga register or memory manipulations to reduce screen flickering. - update(): check variable vga_mem_updated before everything else
- update(): skip screen update if the vertical retrace is in progress
  (using 72 Hz vertical frequency). The vertial retrace phase is often used for
  vga register or memory manipulations to reduce screen flickering.
- update(): check variable vga_mem_updated before everything else

marmolejo/bochs-zet,marmolejo/bochs-zet,marmolejo/bochs-zet,marmolejo/bochs-zet,marmolejo/bochs-zet