21.3.3.1.4 Input Capture Frequency Measurement Mode

In this mode, the TCB captures the counter value and restarts on either a positive or negative edge of the event input signal.

The interrupt flag is automatically cleared after the high byte of the Compare/Capture register (TCBn.CCMP) has been read, and an interrupt request is generated.

The figure below illustrates this mode when configured to act on rising edge.