RTCC with multiple clock source
I'm trying to use RTCC module from PIC24FJ64GA702.
At the moment I'm using LPRC and I successfully obtained the RTCC, nevertheless, experienced user of RTCC might have known that LPRC isn't the most accurate! Indeed, while running a test for 12 hours, the RTCC is giving an error of 40 minutes.
SO I'm trying to switch to a more accurate external clock source. At the moment I'm using an accurate 10 MHz external oscilator. One of the major requirement of the system is power consumption, and I have tried my best to lower current to ~ 4 uA during sleep mode. After enabling primary oscillator in sleep mode to have accurate reading of RTCC, the current increased to about 400 uA, so it seems this is not a solution either.
My MCU has used up all the pins and therefore I can't attach an external secondary clock to the system, this solution seems excluded from the options too.
Could anyone please give me some suggestions how am I going to have an accurate RTCC, say I can accept a few seconds of error a day, while maintaining the low power operation of my systems?
thanks a lot!