
2-50
Computer Group Literature Center Web Site
Raven PCI Host Bridge & Multi-Processor Interrupt Controller
2
registers. If subsequent IPIs are initiated before the first is acknowledged,
only one IPI will be generated. The IPI channels deliver interrupts in the
Direct Mode and can be directed to more than one processor.
8259 Compatibility
The Raven MPIC provides a mechanism to support PC-AT compatible
chip sets using the 8259 interrupt controller architecture. After power-on
reset, the Raven MPIC defaults to 8259 pass-through mode. In this mode,
interrupts from external source number 0 (the interrupt signal from the
8259 is connected to this external interrupt source on the Raven MPIC) are
passed directly to processor 0. If the pass-through mode is disabled, the
8259 interrupts are delivered using the priority and distribution
mechanisms of the Raven MPIC.
The Raven MPIC does not interact with the vector fetch from the 8259
interrupt controller.
Raven-Detected Errors
Raven-detected errors are grouped together and sent to the interrupt logic
as a singular interrupt source. The interrupt delivery mode for this interrupt
is distributed.
For system implementations where the Raven MPIC controller is not used,
the Raven-Detected Error condition will be made available by a signal
which is external to the Raven ASIC. Presumably this signal would be
connected to an externally sourced interrupt input of a MPIC controller in
a different device. Since the MPIC specification defines external I/O
interrupts to operate in the distributed mode, the delivery mode of this
error interrupt should be consistent.
Timers
There is a divide by eight pre-scaler which is synchronized to the Raven
clock (MPC processor clock). The output of the prescaler enables the
decrement of the four timers. The timers may be used for system timing or
to generate periodic interrupts. Each timer has four registers which are
used for configuration and control. They are:
❏
Current Count Register