from netbsd:

Update a kludge from 4.4bsd/pmax: DECstation PROMs force the clock to
be in 1972 or 1973. If the clock is set to the actual time, the PROM
appears to reset the chip date to 1972 at each reboot.
Change the "year offset" from 22 years to 24 years (good till 1997)
until this code is replaced with something that uses the chip as a
seconds-since-beginning-of-year clock (encoded as a date, relative to
1972-01-01 00:00:00).

diff --git a/sys/arch/pmax/pmax/clock.c b/sys/arch/pmax/pmax/clock.c
index 98c3b5e..c4e8d9b 100644 (file)
--- a/sys/arch/pmax/pmax/clock.c
+++ b/sys/arch/pmax/pmax/clock.c
@@ -1,4 +1,4 @@
-/*     $NetBSD: clock.c,v 1.8 1995/08/10 10:50:58 jonathan Exp $       */
+/*     $NetBSD: clock.c,v 1.9 1996/01/07 15:38:44 jonathan Exp $       */
 
 /*
  * Copyright (c) 1988 University of Utah.
@@ -253,8 +253,22 @@ setstatclockrate(newhz)
 /*
  * This is the amount to add to the value stored in the clock chip
  * to get the current year.
+ *
+ * Experimentation (and passing years) show that Decstation PROMS
+ * assume the kernel uses the clock chip as a time-of-year clock.
+ * The PROM assumes the clock is always set to 1972 or 1973, and contains
+ * time-of-year in seconds.   The PROM checks the clock at boot time,
+ * and if it's outside that range, sets it to 1972-01-01.
  */
+#if 1          /* testing, until we write time-of-year code as aboce */
+#define YR_OFFSET      24      /* good til dec 31, 1997 */
+#define DAY_OFFSET     /*1*/ 0
+#else
 #define YR_OFFSET      22
+#define DAY_OFFSET     1
+#endif
+
+#define        BASE_YEAR       1972
 
 /*
  * This code is defunct after 2099.
@@ -288,18 +302,35 @@ inittodr(base)
                badbase = 0;
 
        c = Mach_clock_addr;
-       /* don't read clock registers while they are being updated */
+
+       /*
+        * Don't read clock registers while they are being updated,
+        * and make sure we don't re-read the clock's registers
+        * too often while waiting.
+        */
        s = splclock();
-       while ((c->rega & REGA_UIP) == 1)
-               ;
+       while ((c->rega & REGA_UIP) == 1) {
+               splx(s);
+               DELAY(10);
+               s = splx();
+       }
+
        sec = c->sec;
        min = c->min;
        hour = c->hour;
-       day = c->day + 1;
+       day = c->day;
        mon = c->mon;
-       year = c->year + YR_OFFSET;
+       year = c->year;
+
        splx(s);
 
+#ifdef DEBUG_CLOCK
+       printf("inittodr(): todr hw yy/mm/dd= %d/%d/%d\n", year, mon, day);
+#endif
+       /* convert from PROM time-of-year convention to actual time */
+       day  += DAY_OFFSET;
+       year += YR_OFFSET;
+
        /* simple sanity checks */
        if (year < 70 || mon < 1 || mon > 12 || day < 1 || day > 31 ||
            hour > 23 || min > 59 || sec > 59) {
@@ -352,11 +383,14 @@ resettodr()
 {
        register volatile struct chiptime *c;
        register int t, t2;
-       int sec, min, hour, day, mon, year;
+       int sec, min, hour, day, dow, mon, year;
        int s;
 
-       /* compute the year */
+       /* compute the day of week. */
        t2 = time.tv_sec / SECDAY;
+       dow = (t2 + 4) % 7;     /* 1/1/1970 was thursday */
+
+       /* compute the year */
        year = 69;
        while (t2 >= 0) {       /* whittle off years */
                t = t2;
@@ -382,19 +416,37 @@ resettodr()
        sec = t % 60;
 
        c = Mach_clock_addr;
+
+       /* convert to the  format the PROM uses */
+       day  -= DAY_OFFSET;
+       year -= YR_OFFSET;
+
        s = splclock();
-       t = c->regb;
-       c->regb = t | REGB_SET_TIME;
+       t = c->regd;                            /* reset VRT */
+       c->regb = REGB_SET_TIME | REGB_DATA_MODE | REGB_HOURS_FORMAT;
        MachEmptyWriteBuffer();
+       c->rega = 0x70;                         /* reset time base */
+       MachEmptyWriteBuffer();
+
        c->sec = sec;
        c->min = min;
        c->hour = hour;
-       c->day = day - 1;
+       /*c->dayw = dow;*/
+       c->day = day;
        c->mon = mon;
-       c->year = year - YR_OFFSET;
-       c->regb = t;
+       c->year = year;
+       MachEmptyWriteBuffer();
+
+       c->rega = REGA_TIME_BASE | SELECTED_RATE;
+       c->regb = REGB_PER_INT_ENA | REGB_DATA_MODE | REGB_HOURS_FORMAT;
        MachEmptyWriteBuffer();
        splx(s);
+#ifdef DEBUG_CLOCK
+       printf("resettodr(): todr hw yy/mm/dd= %d/%d/%d\n", year, mon, day);
+#endif
+
+       c->nvram[48*4] |= 1;            /* Set PROM time-valid bit */
+       MachEmptyWriteBuffer();
 }
 
 /*XXX*/