On the MCB2388 plugging the power will result in both the POR and EXTR
bit being set.
Not sure if this is a property of the board, but it means RTC is also
reset after programming, so it behaves just like Backup RAM.
If we woke from Deep Sleep the POR bit will be cleared, so the RTC is not
reset.
Calling localtime() adds considerable overhead.
There are easier ways to set the date to 1970.
For tests/periph_rtc this results in this ROM change:
master:
text data bss dec hex
31328 240 98064 129632 1fa60
with this patch:
text data bss dec hex
20036 140 98168 118344 1ce48
A naive implementation may set a RTC alarm in 30s by calling
struct tm now;
rtc_get_time(&now);
now.tm_sec += 30;
rtc_set_alarm(&now, _cb, NULL);
This works for RTC implementations that use a RTT internally and call
mktime() to convert the struct tm to a unix timestamp, as mktime() will
normalize the struct in the process.
Call rtc_tm_normalize() when the RTC uses separate registers for time / date
components to ensure it is normalized.
This also modifies tests/periph_rtc to exercise this case.
