Tom,
Thanks for the comments ! In my design I am using NMEA as an option to
set initial time on the clock. Its just faster and more convenient than
doing it manually. And in the other (rare) occasions when clock logic
could decide to sync. RTC module time with time received from GPS
module. Basically I decide not to relay on GPS NMEA too much. My clock
using 1PPS signal coming from internal GPS module or from external
source connected to the device. That 1PPS and 32kHz signal from RTC
module, connected to the MCU timers. So, I know for sure if RTC module
generate its 32k signal slower/faster than it should be. If the
difference between of those two signals become too big, clock will do
"autocorrection" for the RTC oscillator to trim the value for Aging
Register. RTC module has accuracy 2ppm. I think it suppose to keep the
time well.
Initially I was thinking that GPS will receive "hh:59:60" NMEA message
and I could use it as it is. But now I think
I'll add some more code to handle such wonderful thing as a "leap second
event". I am going to create subroutines which will allow me to enter
and keep "leaps second" event in battery backed SRAM and apply it as
that even occurred. Unfortunately it will need the human interaction to
set up leap second events. But if I'll leave the clock logic as it is
now, I'll need to correct time on the clock any way. Since 1PPS just
keep RTC oscillator in tact. But time on the clock will be 1 second
ahead.
--
WBW,
V.P.
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