All interrupt vectors other than NMI are assigned to priority level 0 (normal) by default. The user may override this by assigning one of these vectors as a high priority vector. The device will have many normal priority vectors, and some of these may be pending at the same time. Two different scheduling schemes are available to choose which of the pending normal priority interrupts to service first: Static and round robin.
The following sections use the ordered sequence IVEC to explain these scheduling schemes. IVEC is the Interrupt Vector Mapping as listed in the Peripherals and Architecture chapter. IVEC0 is the reset vector, IVEC1 is the NMI vector, and so on. In a vector table with n+1 elements, the vector with the highest vector number is denoted IVECn. Reset, non-maskable interrupts and high-level interrupts are included in the IVEC map, but will be disregarded by the normal priority interrupt scheduler as they are not normal priority interrupts.