Subject: Re: date and time
To: Tino Reinhardt <>
From: Miles Nordin <carton@Ivy.NET>
List: port-mac68k
Date: 02/01/2000 20:20:30
I'm surprised you got this far with a 520.  They have a 68LC040 in them,
so I though there were FPU problems.  I tried mine months ago, and it
worked enough to be intriguing but definitely not useful.

On Tue, 1 Feb 2000, Tino Reinhardt wrote:

> On startup (boot) it shows "PRAM: time does not appear to be read
> correctly" and "check an reset the date".

I believe this means that the time MacOS reported to the Booter app when
you hit Cmd-B and the time read from the clock hardware differ by more
than ten minutes.  They shouldn't, because it only takes a few seconds to
boot.  AFAIK it means no more or less--yet you could spend hours pondering
the subtle implications. :)

Dead battery is one good theory, but maybe not the only one.

> "netbsd does not trust itself to set the RTC". Hm. What does this
> mean?

My understanding is a bit sketchy and likely to be flawed on these
points.  I believe most architectures go like this:

1. At boot, set the ``software'' Unix clock based on the battery-powered
   clock hardware.
2. During operation, adjust the Unix clock as required, with xntp, with
   'date,' and advance it based on the same ``timer'' interrupts that 
   provoke preemptive multitasking context switching--interrupts which
   usually do _not_ come from the battery-powered clock.
3. At shutdown, write the Unix clock's time into the battery-powered
   clock's registers.

mac68k skips Step 3, because the Unix clock is inaccurate, usually loses
time rapidly on that architecture.  It ``does not trust itself'' to know
what time it is better than the battery clock already does.  Thus, NetBSD
will never update the battery clock on a mac68k.

The best way to verify that you do indeed have a dead battery would
probably be to install the MacOS Date & Time control panel, and see if the
date/time settings will ``stick.'' You can download full install disks of
old revisions of MacOS for free from

I've had my 520 apart far enough to replace the battery several times, and
wouldn't hesitate to reccommend the procedure if you need to do it and
can find someone to sell you a battery cheaply. The machines are worth
very little if you break them anyway.  I think you have to take the screen
off, so just be careful of the flimsy screen cable and the weak plastic
plugs on the end(s) of it.

You can make your newly purchased clock battery run down less by always
giving the Mac a charged NiMH battery or an AC adapter from which to suck
power, even while it's supposedly ``off''--Apple's TIL reccommends this
for most of their laptops.

Miles Nordin / v:+1 720 841-8308 fax:+1 530 579-8680
555 Bryant Street PMB 182 / Palo Alto, CA 94301-1700 / US