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Raven PCI Host Bridge & Multi-Processor Interrupt Controller Chip
2
interrupt vector indicates the interrupt source is the 8259, the
interrupt handler issues a second Interrupt Acknowledge request to
read the interrupt vector from the 8259. The RavenMPIC does not
interact with the vector fetch from the 8259.
5. The interrupt handler saves the processor state and other interrupt-
specific information in system memory and re-enables for external
interrupts (the MSRee bit is set to 1). RavenMPIC blocks interrupts
from sources with equal or lower priority until an End-of-Interrupt
is received for that interrupt source. Interrupts from higher priority
interrupt sources continue to be enabled. If the interrupt source was
the 8259, the interrupt handler issues an EOI request to the
RavenMPIC. This resets the In-Service bit for the 8259 within the
RavenMPIC and allows it to recognize higher priority interrupt
requests, if any, from the 8259. If none of the nested interrupt modes
of the 8259 are enabled, the interrupt handler issues an EOI request
to the 8259.
a. The device driver interrupt service routine associated with this
interrupt vector is invoked.
b. If the interrupt source was not the 8259, the interrupt handler
issues an EOI request for this interrupt vector to the
RavenMPIC. If the interrupt source was the 8259 and any of the
nested interrupt modes of the 8259 are enabled, the interrupt
handler issues an EOI request to the 8259.
Normally, interrupts from ISA devices are connected to the 8259
interrupt controller. ISA devices typically rely on the 8259 Interrupt
Acknowledge to flush buffers between the ISA device and system
memory. If interrupts from ISA devices are directly connected to the
RavenMPIC (bypassing the 8259), the device driver interrupt
service routine must read status from the ISA device to ensure
buffers between the device and system memory are flushed.
Reset State
After a power-on reset the RavenMPIC state is:
❏
Current task priority for all CPUs set to 15.