Processor's Current Task Priority; Nesting Of Interrupt Events; Spurious Vector Generation - Motorola MVME5100 Programmer's Reference Manual

Hawk PCI Host Bridge & Multi-Processor Interrupt Controller

Processor's Current Task Priority

2

Nesting of Interrupt Events

Spurious Vector Generation

2-54
Each processor has a task priority register which is set by system software
to indicate the relative importance of the task running on that processor.
The processor will not receive interrupts with a priority level equal to or
lower than its current task priority. Therefore, setting the current task
priority to 15 prohibits the delivery of all interrupts to the associated
processor.
A processor is guaranteed never to have an in service interrupt preempted
by an equal or lower priority source. An interrupt is considered to be in
service from the time its vector is returned during an interrupt
acknowledge cycle until an EOI (End of Interrupt) is received for that
interrupt. The EOI cycle indicates the end of processing for the highest
priority in service interrupt.
Under certain circumstances the MPIC will not have a valid vector to
return to the processor during an interrupt acknowledge cycle. In these
cases the spurious vector from the spurious vector register will be returned.
The following cases would cause a spurious vector fetch:
INT is asserted in response to an externally sourced interrupt, which
is activated with level sensitive logic, and the asserted level is
negated before the interrupt is acknowledged.
INT is asserted for an interrupt source, which is masked using the
mask bit, in the Vector-Priority register before the interrupt is
acknowledged.
Computer Group Literature Center Web Site