14.3.2.4 Interrupt Priority

All interrupt vectors are assigned to one of three possible priority levels, as shown in the table below. An interrupt request from a high-priority source will interrupt any ongoing interrupt handler from a normal-priority source. When returning from the high-priority interrupt handler, the execution of the normal-priority interrupt handler will resume.
Table 14-2. Interrupt Priority Levels
PriorityLevelSource
HighestNon-Maskable InterruptDevice-dependent and statically assigned
...Level 1 (high priority)One vector is optionally user selectable as level 1
LowestLevel 0 (normal priority)The remaining interrupt vectors