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INTERRUPTS
Checking Pending Interrupts — The interrupt controller compares each pending interrupt's priority
with the current process priority. If process priority changes, posted interrupts of higher priority are
then serviced. Comparing the process priority to posted interrupt priority is handled differently for
hardware and software interrupts. Each hardware interrupt is assigned a specific priority when the
processor is configured. The priority of all posted hardware interrupts is continually compared to
the current process priority. Software interrupts are posted in the interrupt table in external
memory. The highest priority posted in this table is also saved in an on-chip software priority
register; this register is continually compared to the current process priority.
Servicing Interrupts — If the process priority falls below that of any posted interrupt, the interrupt
is serviced. The comparator signals the core to begin a microcode sequence to perform the
interrupt context switch and branch to the first instruction of the interrupt routine.
Figure 11-12
illustrates interrupt controller function. For best performance, the interrupt flow for
hardware interrupt sources is implemented entirely in hardware.
The comparator signals the core only when a posted interrupt is a higher priority than the process
priority. Because the comparator function is implemented in hardware, microcode cycles are never
consumed unless an interrupt is serviced.
11
11-29
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