14.3.2.1 Enabling, Disabling, and Resetting
Global enabling of interrupts is done by writing a '1' to the Global Interrupt Enable bit (I) in the CPU Status register (CPU.SREG). To disable interrupts globally, write a '0' to the I bit in CPU.SREG.
The desired interrupt lines must also be enabled in the respective peripheral, by writing to the peripheral's Interrupt Control register (peripheral.INTCTRL).
Interrupt flags are not automatically cleared after the interrupt is executed. The respective INTFLAGS register descriptions provide information on how to clear specific flags.