Docs at page 7 of
https://datasheets.maximintegrated.com/en/ds/DS1921H-DS1921Z.pdf
<https://datasheets.maximintegrated.com/en/ds/DS1921H-DS1921Z.pdf> are not very
clear, but I would bet that
1 = Jan
2 = Feb
…
so that conversions at
https://github.com/owfs/owfs/blob/ba66022f115909396a4b939f37e8c3ee8d293862/module/owlib/src/c/ow_1921.c#L1014
https://github.com/owfs/owfs/blob/ba66022f115909396a4b939f37e8c3ee8d293862/module/owlib/src/c/ow_1921.c#L1072
<https://github.com/owfs/owfs/blob/ba66022f115909396a4b939f37e8c3ee8d293862/module/owlib/src/c/ow_1921.c#L1072>
are off by one.
The best way to test for this is simply set the RTC at 23:59 and observe how
the day/month registers are incremented. Actual code assumes that we have
Day31 Month00 -> Day01 Month01
Day28 Month01 -> Day01 Month02
but there is the possibility that the registers actually go
Day31 Month01 -> Day01 Month02
Day28 Month02 -> Day01 Month03
Stefano
BTW, I never really understood why in C the broken down time struct_tm has days
numbered from 1 to 31, but month numbered from 0 to 11:
struct tm {
int tm_sec; /* seconds after the minute [0-60] */
int tm_min; /* minutes after the hour [0-59] */
int tm_hour; /* hours since midnight [0-23] */
int tm_mday; /* day of the month [1-31] */
int tm_mon; /* months since January [0-11] */
int tm_year; /* years since 1900 */
int tm_wday; /* days since Sunday [0-6] */
int tm_yday; /* days since January 1 [0-365] */
int tm_isdst; /* Daylight Savings Time flag */
long tm_gmtoff; /* offset from UTC in seconds */
char *tm_zone; /* timezone abbreviation */
};
the most common explanation being that tm_mday is always used as is, but tm_mon
is mostly used as an index in an array of month names, thus starting from 0.
> On 22 Aug 2018, at 19:50, Jan Kandziora <j...@gmx.de> wrote:
>
> Am 22.08.2018 um 16:16 schrieb Ben Oliver:
>> I'm having issues with clock settings on a DS1921 going from windows to
>> owfs on linux, and vice-versa.
>>
>> I (on owfs) set the time like this:
>>
>> echo "$(date +%s)" > "clock/udate"
>>
> Which version of owfs do you use?
>
> $ owfs --version
>
>
>
> Owlib (owfs) uses gmtime_r() to turn the seconds till 1970-01-01 UTC
> into a representation the DS1921 understands.
>
> https://github.com/owfs/owfs/blob/master/module/owlib/src/c/ow_1921.c#L1065
>
> This function assumes January == 0.
>
> Unfortunately, the DS1921 datasheet does not state whether January is 0
> or 1. Others have the same problem:
>
> https://github.com/dustin/ibutton/blob/master/mlan/ds1921.c#L53
>
>
> So far, I see only one way to find it out who's correct, check whether
> the February, 29th correction the chip does works right with owlib or not.
>
> Volunteers? Maybe Paul (or others) had checked that already in the past?
>
> Kind regards
>
> Jan
>
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