Specifications

Interrupt Controller (V40)
Automatic Priority Rotation
Automatic priority rotation is used in applications with interrupt
devices that are of equal priority. In this mode of operation, after an
interrupt request is serviced the ICU rotates it into the lowest priority
slot. This guarantees that all interrupt requests will be serviced. The
nonspecific FI or specific FI commands can be used for automatic
priority rotation.
Rotate on Nonspecific FI
The ICU response to a rotate on nonspecific FI is the same as
previously discussed, except that the interrupt request is rotated into
the lowest priority position after the IIS bit of the Interrupt In-Service
is cleared. The other ICU inputs are also rotated into the next higher
priority position.
Rotate on Self Finish FI
The ICU handles a rotate on self finish FI in much the same manner
as the self finish FI previously discussed. The difference is that
priority rotation is done automatically after the IIS bit is reset. The
same precautions discussed under the self finish FI explanation still
apply.
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