The disk subsystem uses two ports on the system's  8520 cia  chips, and
several registers in the Paula chip:

   ciaapra    ($bfe001)    four input bits for disk sensing
   ciabprb    ($bfd100)    eight output bits for disk selection, control
                             and stepping
   adkcon     ($dff09e)    control bits (write only register)
   adkconr    ($dff010)    control bits (read only register)
   dskpth     ($dff020)    dma pointer (32 bits)
   dsklen     ($dff024)    length of dma
   dskbytr    ($dff01a)    disk data byte and status read
   dsksync    ($dff07e)    disk sync finder; holds a match word