Teensy 3.0 FreqCounter

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recri

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Hi all --

I was looking at implementing a frequency counter on the Teensy 3.0 using the general scheme of the Arduino FreqCounter library. So we look for a timer that can count incoming pulses, gate it on for a period, and see how many counts we get during the period.

So, the Flex Timer modules can count an external clock, referred to as EXTCLK in Section 35.2, page 692 of the tome. That signal name appears nowhere else in the documentation that Acrobat can find. In Section 3.8.2.2, page 105 the external clock pins are referred to as FTM_CLKINx, and there are two signals in the pinout chapter of the lesser tome, FTM_CLKIN0 and FTM_CLKIN1.

Those two signals are on pins 32 and 33, which correspond to A18 and A19, which are not even mentioned in hardware/teensy/cores/teensy3/core_pins.h. There are a few A pins which are called out as not available to the user: A0, A1, A2, and A3. But A18 and A19 appear to have been forgotten entirely. Oh, they're the pins where the external crystal connects.

Is this correct? Is there some other way to get hardware to count pulses from an external source on the Teensy 3.0? I guess I'll see how far I get with pin change interrupts.

-- rec --
 
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