Agnus/
                  Read/   Denise/
Register Address  Write   Paula         Function
-------- -------  -----   -------       --------
DSKLEN     024      W       P     Disk length

                 This register contains the length (number of words)
                 of disk DMA data. It also contains two control
                 bits, a DMA enable bit, and a DMA direction
                 (read/write) bit.

                 BIT#  FUNCTION      DESCRIPTION
                 ----  -----------   --------------------------------
                 15    DMAEN         Disk DMA enable
                 14    WRITE         Disk write (RAM to disk) if 1
                 13-0  LENGTH        Length (# of words) of DMA data.