Teensy 3.6 RTC Performance Below Freezing

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RFModulator

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Does anybody have any data or experience with how accurate the Teensy 3.6 RTC is when it's in an environment ranging from 0 to 32 degrees Fahrenheit? Do any existing functions allow for RTC compensation via temperature readings? I took a look at the datasheet (Page 1340, Section 49.4.3: Compensation) and it seems that the K66 has the ability to use temperature for RTC compensation. However, while looking around here, it doesn't seem like anybody has implemented that functionality yet.

Some additional information:

I'm working on a project with a Teensy 3.6 that has been sitting outside since the beginning of January. Temperatures here (Pennsylvania) tend to go between 0 and 30 degrees Fahrenheit in Winter (and occasionally below 0, but not very often). Because the Teensy was in a remote location, I couldn't check on it regularly. It seemed to work just fine for the first few weeks, then during a cold spell where the battery died due to excessive snow on the solar panels, the RTC somehow lost a couple of weeks' worth of time when it came back up. It's certainly possible that my code caused a buffer overrun or something that held things up; it seems implausible that sub-0 temperatures would cause the RTC to loose several weeks. Regardless, that got me thinking about how much accuracy I should expect from the RTC when it's particularly cold out.
 
Teensy3Clock.compensate(num)
The compensate() function lets to adjust the speed of the clock slightly. If it’s running too fast, call compensate() with a negative number to slow it down a bit. The adjustment is approximately the ppm/8. If you use compensate(-40), the clock is slowed by 5 ppm (parts per million).
 
Oh, awesome! I didn't realize that function existed. Thanks, CHris! It seems like there's a decent bit out there about how it works, so I feel embarrassed that I missed it. I'll have to sit down and do some thinking about how to implement it. I may be back with questions.

If anybody has general experience/data about how their Teensy has performed in sub-freezing temperatures, I'm still interested to hear about it.
 
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