AVR32AP datasheet(33/181 Pages) ATMEL

33 / 181 page

32001A–AVR32–06/06

AVR32

privileged memory protection region. In a segmented AVR32B system, some segments of the

virtual memory space may be better suited than others for holding event handlers. This is due to

differences in translateability and cacheability between segments. A cacheable, non-translated

segment may offer the best performance for event handlers, as this will eliminate any TLB

misses and speed up instruction fetch. The user may also consider to lock the event handlers in

the instruction cache.

If several events occur on the same instruction, they are handled in a prioritized way. The priority

ordering is presented in Table 3-2. If events occur on several instructions at different locations in

the pipeline, the events on the oldest instruction are always handled before any events on any

younger instruction, even if the younger instruction has events of higher priority than the oldest

instruction. An instruction B is younger than an instruction A if it was sent down the pipeline later

than A.

The addresses and priority of simultaneous events are shown in Table 3-2 on page 34

The interrupt system requires that an interrupt controller is present outside the core in order to

prioritize requests and generate a correct offset if more than one interrupt source exists for each

priority level. An interrupt controller generating different offsets depending on interrupt request

source is referred to as autovectoring. Note that the interrupt controller should generate

autovector addresses that do not conflict with addresses in use by other events or regular pro-

gram code.

The addresses of the interrupt routines are calculated by adding the address on the autovector

offset bus to the value of the Exception Vector Base Address (EVBA). In AVR32 AP, the actual

autovector address is formed by bitwise OR-ing the autovector offset to EVBA. Using bitwise-OR

instead of an adder saves hardware. The programmer must consider this when setting up

EVBA.

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