Memory access delays

[Clownacy]

The CPU interpreters currently do not support delays of any form. However, I know of many that occur on real Mega Drives:

• Work RAM delays
• 68k being delayed when accessing its memory bus during a VDP Transfer.
  • Z80 accessing the 68k bus during this.
• 68k writing to the VDP while its FIFO is full.
  • 68k reading from the VDP while its FIFO is empty?
• The mysterious so-called "DRAM refreshes" (I think the Overdrive II document explains this one).
• Z80 cycle-stealing.