srctime (text_src, int_cal);
Enable the RTCC’s clocking source and specifies calibration value for the crystal drift. Two choices for the first parameter are possible:
“LPRC” selects the PIC32’s internal low power clock.
“SOSC” selects an external secondary 32.768 kHz clock connected to port 48.
The calibration value is typically 0, but can be changed in the range -512 … +511 adjusted clocks per minute.
On very first initialisation, Rittle tries to enable the external oscillator first, and falls back to the internal LPRC in case there is no clock coming on port 48.