Motorola MVME2300 Series - Manual (Page 131)

Raven Interrupt Controller
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The RavenMPIC receives interrupt inputs from:
❏ 16 external sources
❏ Four interprocessor sources
❏ Four timer sources
❏ One Raven internal error detection source
Externally sourced interrupts 1 through 15 have two modes of activation:
low level or active high positive edge. External interrupt 0 can be either
level- or edge-activated with either polarity. The Interprocessor and timer
interrupts are event-activated.
Readability of CSR
Unless explicitly specified, all registers are readable and return the last
value written. The exceptions are the IPI dispatch registers and the EOI
registers which return 0s on reads, the interrupt source ACT bit which
returns current interrupt source status, the interrupt acknowledge register
which returns the vector of the highest-priority currently pending interrupt,
and reserved bits which return 0s. The interrupt acknowledge register is
also the only register which exhibits any read side-effects.
Interrupt Source Priority
Each interrupt source is assigned a priority value in the range from 0 to 15,
where 15 is the highest priority level. For delivery of an interrupt to take
place, the priority of the source must be greater than that of the destination
processor. Therefore, setting a source priority to zero inhibits that
interrupt.
Processor’s Current Task Priority
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.