clock *gains* time on my machine!

[Keith Packard]

I have the most bizarre problem on my pdp11/73 running 2.9bsd.  The
time kept by the kernel is faster than it should be!  It seems to
be gaining little by little as if there were more than 60 interrupts
per second on the bus.

It must be a hardware problem as I recently installed the computer in
a new backplane and installed 4 new serial ports; before doing so
the clock remained sane for weeks on end, now it gains about a minute
in twenty.

The hardware in question is a 4x4 Q-bus backplane (ba11-ma).  It has
switches for dc-power, halt/enable and line-time-clock enable.
It also has dc-ok and run indicators, the dc-ok indicator is lit
but the run indicator is not.

I have heard rumor and in fact experienced systems that *lose* time
as a result of ignored clock interrupts but I have never seen
a system *gain* time.

For now I am reading my time-of-day clock board every 5 minutes from
cron so that it stays reasonably in sync.

keith packard
...!tektronix!reed!motel6!keith		<- the machine in question
...!tektronix!azure!keithp
...!tektronix!reed!keith
(503) 771-1305