The EIC must be initialized in the
following order:
- Enable CLK_EIC_APB
- If edge detection or filtering is
required, GCLK_EIC must be enabled
- Write the EIC configuration
registers (EVCTRL, WAKEUP, CONFIGy)
- Enable the EIC
To use NMI, GCLK_EIC must be enabled after
EIC configuration (NMICTRL).