• If you could measure the difference in time between the 1pps output of the GPS receiver and the 1Hz output of the RTC then you could discipline the RTC using the ageing offset register. A 1-bit change in the register should change the oscillator frequency by one ppm.

    I don't know if espruino could measure time that accurately but you might be able to measure using a sample and hold ADC against a capacitor, or some analogue/PWM capture using the Waveform class? Initiated by an Interupt caused by the 1pps you should have time to work out the error.


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