As a third step to learning the Teensy LC, I decided to tackle input capture. I discovered that there is no separate interrupt vector for input capture; it is the same vector used by the timer interrupt. This means that if we are looking for a timer overflow event as well as a pin change for input capture, we must check for that specific interrupt flag within the interrupt service routine (ISR).
As a follow-on to my PWM experiments, I wanted to create a custom interrupt service routine (ISR) in the Teensy LC. This would be similar to using the ISR() macro in an ATmega-based Arduino. Because the ARM has different vectors (and some other weird/cool things, like configurable interrupt priority levels), I knew the normal ATmega vectors would not work. Luckily, PJRC created a set of vectors to work with the Teensy, which can be found in this code.
You don’t need any additional components for this example. We are just going to flash the on-board LED using our custom ISR.