David Johnson-Davies published a new project on his blog. This project is a simple frequency meter capable of measuring frequencies up to 100MHz with an accuracy of 0.002%. Based on an ATtiny414, it demonstrates the use of Timer/Counter TCD0 and the Event System:
I recently wanted to design a frequency meter that would measure up to 100MHz, so you can use it to test processor clocks and crystals. There are many designs for microcontroller-based frequency meters on the web; after all, it’s one of the applications that the timer/counters in most microcontrollers are designed for. However, most of them don’t go as high as 100MHz because the microcontroller’s own clock usually imposes an upper limit of half the clock frequency.
100MHz Frequency Meter using ATtiny414 – [Link]