Re: Thunder Clock

[dempson@atlantis.actrix.gen.nz (David Empson)]

In article <4a4bv5$g9e@nntp5.u.washington.edu>,
Derek Peschel <dpeschel@u.washington.edu> wrote:
> In article <DJ5789.D11.0.queen@torfree.net>,
> Hans Ruschka <bw199@torfree.net> wrote:
> 
> >I use a enhanced 2e with a Thunderclock in slot#5.  The clock works fine 
> >as long as I use a Prodos Version 1.9..  As soon as I switch to a version 
> >2.0.., the clock shows the year 1987 and can not be reset to 1995!!  Back 
> >to Prodos 1.9. and everything is ok.  
> 
> In a way, ProDOS doesn't know if the year is 1987, or 1995, or whatever.
> The Thunderclock only keeps track of an eight-year range, which ProDOS
> converts to a useful form.  Since you can't change the number of years in
> the clock's "calendar," you need to patch ProDOS instead.

It is even simpler than that.  The method used by ProDOS to get the
time from the ThunderClock doesn't even indicate which year it is.  (I
don't know if the ThunderClock stores the year.)

ProDOS's ThunderClock driver has a seven-entry table for calculating
which year it is.  The calculation is based on the month, day of month
and day of week.  Due to leap years, at least one entry in the table
is repeated, so the range of years that can be supported is only five
or six.

In other words, if you have a ThunderClock, then you will need to patch
all your boot copies of ProDOS every five or six years to update the
year table.  The patch program was included on recent Apple II system
disks.  I think it supports ProDOS-8 1.9 and later versions.

> It sounds like you have a patched version of ProDOS 1.9, and an unpatched
> version of ProDOS 2.0.

Correct.

-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand