Why does IntervalTimer restrict cycles to >= 36?

[shawn]

I was wondering why IntervalTimer restricts cycles to be >= 36 for all Teensys? I know that Teensy 3 can have F_BUS at 24, 36 ,or 48 cycles/microsecond, but the Teensy 4 uses 24 cycles/microsecond in its IntervalTimer implementation and cycles is still restricted to >= 36.

Links:

1. https://github.com/PaulStoffregen/c...d4862212a8965e3ff/teensy4/IntervalTimer.h#L53
2. https://github.com/PaulStoffregen/c...d4862212a8965e3ff/teensy3/IntervalTimer.h#L54