Notes for implementors of drivers
           ---------------------------------
 
 Before  recompiling  source  files, new EXT files should be generated.
 This reduces the chances of cross-module confusion.
 
 When  recompiling all the source files, one should be careful that the
 include files are all in the correct state.  Especially,  MACHINE.CST,
 which  contains  machine  dependent  timing  loop variables, which are
 mainly used in the screen drivers.
 
 In  order  to  set  these variables, a version of the SOFT terminal is
 compiled.  There are two loop constants.
 1.   NLOOPS.  When in setup mode, and Ctrl G is keyed, there should be
      a delay of 10 seconds, then a bell.
 2.   NWAIT.   When  in  normal terminal mode, ESC ?, should attempt to
      restart an SSMP session, giving a 20  second  delay  between  the
      messages on the screen.
 
 Files  MDRV: APRICOT.LIB, NIMBUS.LIB, IBM.LIB, NIMDCC.LIB, AMSTRAD.LIB
 contain details of how to produce the object libraries using PROLIB.
 e.g.  PROLIB @APRICOT.LIB      will produce APRICOT.OBJ.
 
 
 Nimbus  line-drivers  are now implemented for AUX RS422, Piconet COM1,
 and DCC card, (Data  Comms  Controller).   Hence  there  are  now  two
 different  versions  of  the  Nimbus object libraries.  NIMAUX.OBJ and
 NIMDCC.OBJ.  These are  now  linked  using  ZLAUX.OBJ,  ZLASM.OBJ  and
 COMMS.OBJ,  for  NIMAUX,  and  ZLDCC.OBJ ZLASMD.OBJ and DCOMMS.OBJ for
 NIMDCC.  NIMBUS.OBJ is retained as a direct copy of NIMAUX, so as  not
 to  confuse naive users.  Likewise, ZLASM.ASM is retained as a copy of
 ZL422.OBJ.