Crystal Dream II notes:

- Flickering issues, problems with vertical retrace timing.

  If playing to GUS or Sound Blaster, the demo attempt to measure
  the VGA refresh rate, then use IRQ 0 as sort of a vertical retrace
  interrupt to synchronize demo page flipping and rendering to
  the display.

  For reasons unknown to me at this time, the demo will misdetect
  VGA timing if core=dynamic. The dynamic core seems to throw off
  the demo's VGA timing code.

  If demo effects jump, run too fast/slow, and generally flicker
  on screen, then the demo has misdetected the VGA refresh rate
  and the timer is not synchronized with vertical retrace.

  To avoid this problem, set core=normal or core=full.

