tom dunigan
LPC1768 RTC frequency check with WDT. Compare RTC against MCU's microsecond Timer.
Check LPC1768 RTC crystal frequency using WDT. Measure with MCU's microsecond Timer. The MCU's crystal may be off a bit as well. I measured the RTC frequency error at 22 ppm. The spec for the RTC crystal is 20 ppm. Using NTP and a GPS, I had measured the MCU's crystal frequency error at -2 ppm.
Frequency measurements for other MCU/RTC cyrstals at
https://github.com/manitou48/crystals/blob/master/crystals.txt