From: utzoo!decvax!ittvax!tpdcvax!bobvan
Newsgroups: net.unix-wizards
Title: Time of year for kernel changes
Article-I.D.: tpdcvax.190
Posted: Fri Oct 29 11:25:46 1982
Received: Sat Oct 30 02:37:13 1982

This is an appropriate time of year for me to confess to a rather
questionable hack that I put into our Berkeley UNIX kernel some time
ago.  We must run VMS at least once per day, sometimes twice per day.
Those of you who've done this know that the time of day has to be reset
each time we change operating systems.  It really is a pity too.  Code
in machdep.c goes to great lengths to keep the hardware clock register in
the same form as VMS.  However, UNIX uses GMT and VMS uses local time.
We had to set the clock ahead or back 6 hours every time we changed
operating systems.

This lead to operating screw ups on at least two occasions.  The clock
would accidentally be set off by an hour or a day, and it was never
possible to keep the clock set accurately.  Being much more adept at
changing UNIX than VMS, I slipped the appropriate +6 and -6 into the
code in machdep.c and all has been fine until now.

It is appropriate to tell you about this now because I have to change
the 6's to 5's this weekend when we go from CDT to CST.  The
alternative is to put all of that ugly "is this the last Sunday of
October" code from ctime.c into the kernel.  Neither solution is very
good (any better ideas?).  Even if I get hit by a beer truck and the
kernel never gets changed again, we can go back to resetting the clock
twice per day if we have to.

I've included diff's for others in the "two OS" boat with us.

				Only constructive flames, please.
	        (look!  An oxymoron! ^^^^^^^^^^^^^^^^^^^)

				Bob Van Valzah
				(...!decvax!ittvax!tpdcvax!bobvan)

*** machdep.old.c	Thu Sep  9 16:51:44 1982
--- machdep.c	Thu Sep  9 17:08:27 1982
***************
*** 187,193
  clkinit(base)
  	time_t base;
  {
! 	register unsigned todr = mfpr(TODR);
  	long deltat;
  	int year = YRREF;
  

--- 187,198 -----
  clkinit(base)
  	time_t base;
  {
! 	/*
! 	 * RAV todr is kept fudged so date doesn't have to be set
! 	 * when going to VMS.  Change "timezone-60" to "timezone"
! 	 * (both here and below) when we go off daylight savings time.
! 	 */
! 	register unsigned todr = mfpr(TODR)+(timezone-60)*60*100;
  	long deltat;
  	int year = YRREF;
  
***************
*** 268,274
  		yrtime -= secyr;
  		year++;
  	}
! 	mtpr(TODR, TODRZERO + yrtime*100);
  }
  
  #ifdef PGINPROF

--- 273,279 -----
  		yrtime -= secyr;
  		year++;
  	}
! 	mtpr(TODR, TODRZERO + yrtime*100 - (timezone-60)*60*100);
  }
  
  #ifdef PGINPROF