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 1. Interrupt Priority Levels
Priority Level Source
Highest Non-Maskable Interrupt Device-dependent and statically assigned
... Level 1 (high priority) One vector is optionally user selectable as level 1
Lowest Level 0 (normal priority) The remaining interrupt vectors