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	Notes on DTCERT for the Installer
	
	
	
	Note  on  PI  assignment.  DTCERT must run on a channel high
	enough so it does not get the  error  message  DATA  MISSED.
	Anything  higher  is  nice  but  not  necessary.  PI1 is the
	highest priority level and PI7 is the lowest.   The  easiest
	way  to  find  out what channel to run DTCERT on is by trial
	(unless you know how your system PI channels are  used.   If
	so,  DTCERT  will need to be higher than the clock).  At the
	University of Arizona, due  to  our  configuration,  we  run
	DTCERT  on  PI  channel 1.  Other sites may wish to start by
	setting the symbol PIA to 4.  Assemble  DTCERT  as  per  the
	instructions  below.   Run  DTCERT  and  try to certify some
	tapes.  If you get the message DATA MISSED, reassemble for a
	higher  PI  channel.   If  you  get  the  message RATTRP UUO
	FAILED, you either are not priviliged or the PI  channel  is
	occupied  by  a  BLKI/O  and cannot be used by this program.
	Try all  the  PI  channels  until  you  have  tried  PI1  if
	necessary.
	
	DTCERT  must  interupt  the  processer  once ever 400uS when
	writing the timing marks and spends about 50uS  to  90uS  at
	interrupt  level when doing so.  If you get DATA MISSED even
	on the highest PI channel, it  may  be  necessary  that  you
	certify  DECtapes  on  a lightly loaded system (not on prime
	shift).  DTCERT will use about 12% to 20% of  the  processer
	when certifying tapes depending on the processer used.
	
	The  author  has certified DECTAPEs in the middle of the day
	when the system was heavily loaded on KI-10s and  on  KL-10s
	and  found  that DATA MISSED errors occur every 3 to 4 tapes
	certified.  We know of nothing that can be done.  Some other
	program  is  probably  spending  too  much  time with the PI
	system disabled or at a  higher  channel  every  once  in  a
	while.   The  only  known  solution is to try to certify the
	tape again.  We have never had any  trouble  with  any  tape
	certified or recertified using this DTCERT program.

	Assembly instructions:
	
	.R MACRO
	*DTCERT,DTCERT/CREF=DTCERT
	*^C
	.LOAD DTCERT.REL
	.SAVE DTCERT
	.R CREF
	*DTCERT.LST=DTCERT.CRF
	*^C
	
	
	
	
	
	
	If you have any problems with DTCERT, please report them to the
	University of Arizona Computer Center so that they may be repaired.
	Suggested code and enhancements are welcome.
	
		Chris Janton
		System Programmer
		University of Arizona Computer Center
		Tucson, Arizona  85721
	
		Phone: (602) 884-1233