19.6.2.1 Initialization

The EIC must be initialized in the following order:
  1. Enable CLK_EIC_APB
  2. If edge detection or filtering is required, GCLK_EIC must be enabled
  3. Write the EIC configuration registers (EVCTRL, WAKEUP, CONFIGy)
  4. Enable the EIC

To use NMI, GCLK_EIC must be enabled after EIC configuration (NMICTRL).