manitou
Senior Member+
From this discussion, https://community.nxp.com/thread/378715, I learned you can get 1/32768 second precision from the teeny 3* RTC. Here is a simple demo of combining RTC_TPR with RTC_TSR to get RTC millis
https://github.com/manitou48/teensy3/blob/master/RTCms.ino
The actual accuracy of the RTC time and frequency is another matter.
Some anecdotal frequency accuracy data (ppm) for various MCUs:
https://github.com/manitou48/crystals/blob/master/crystals.txt
I don't yet know the specs/part for the T3.5/3.6 crystals.
Teensy Time library
https://github.com/manitou48/teensy3/blob/master/RTCms.ino
The actual accuracy of the RTC time and frequency is another matter.
Some anecdotal frequency accuracy data (ppm) for various MCUs:
https://github.com/manitou48/crystals/blob/master/crystals.txt
I don't yet know the specs/part for the T3.5/3.6 crystals.
Teensy Time library