Hi, I am developing a coin cell powered NRF51-based device that needs to keep track of reasonably accurate real time (no calendar, just number of seconds) in a long term - we're talking months or even years.
To save power the NRF51 should be most of the time in off/sleep mode, waked up only for short periods of time via GPIO (tactile switch). The only thing that needs to keep running continuously is actually the clock itself (all peripheral including radio will be most of the time off).
The question therefore is - is it possible to use internal RTC mechanism for this task (and overcome somehow all obstacles such as sd_power_system_off(), softdevice or application crashes, watchdog resets, etc), or is it more reasonable to use external IC (such as DS1302)?
