I'm playing about with a Dallas  RTC iButton DS1994.

I have a query about the Maxim suggested algorithm for converting
time to seconds. I'm obviously missing a subtlety, I just can't see
what it is.

My Algorithm to convert datetime to seconds. Using year 2000 as year
zero.

elapsed_days =365 * (year-2000) + LeapDay(1) + no_of_whole_month_days
+ number_of_current_month_days + LeapFlag - 1

elapsed_seconds= 86400 * elapsed_days + secs +  (60 * minutes) +
(3600 * hours)

Maxim/Dallas have the following method


      Sv = td->year + 32 - 2000;    I don't understand the reason for
the 32.

Xv = 365 * (Sv-2) + (Sv-1)/4 + dm[td->month] + td->day + Bv - 1;

Xv = 86400 * Xv + (ulong)(td->second) + 60*((ulong)(td->minute) +
60*(ulong)(td->hour));

I can't see why they have the Sv-2 and Sv-1/4 correction. There is an
error in there program I noticed the hours should be multiplied by
3600 and not as they have 60. They use 1970 as year zero.

At this moment I can only assume the 32 is a type of error correction
mechanism in case of transmission failure. The Leap year flag is
calculated earlier on in the program.

 After this I just hope everything will fit into my 873.

any thoughts much appreciated.

Colin
--
cdb, cdb@barnard.name on 31/03/2002

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