Maximum frequency when using FreqCount

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ed_cetera

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In my current project, I use a Teensy 3.1 and the FreqCount library to count the number of high frequency (several MHz) events within a given timeframe. Now I want to know how fast this setup is able to count reliably. The FreqCount website as well as the source code say

"up to 65 MHz with Teensy 3.0 & 3.1" and "LPTMR on Teensy 3.1 can do 65 MHz!".

However, the manual of the processor (p. 918) says

"NOTE The clock source or pulse input source selected for the LPTMR should not exceed the frequency f_LPTMR defined in the device datasheet."

which according to the technical datasheet (p. 19) is

"f_LPTMR | Max. 25 MHz".

What is the highest frequency for reliable counting with the FreqCount library and why? (In particular, where does the 65 MHz value originate from?)
 
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