2-50
Functional Description
2.2.17 Interrupt Routing
This section documents the recommended approach to RAID ready
interrupt routing for the LSI53C895A. In order to be compatible with AMI
RAID upgrade products and the LSI53C895A, the following requirements
must be met:
•
When a RAID upgrade card is installed in the upgrade slot, interrupts
from the mainboard SCSI controller(s) assigned to the RAID upgrade
card must be routed to INTB/, INTC/ and INTD/ of the upgrade slot
and isolated from the mainboard interrupt controller. The system
processor must not see interrupts from the SCSI controllers that are
to be serviced by the RAID upgrade card. An upgrade slot is one that
is connected to the interrupt routing logic for mainboard SCSI
device(s). When a PCI RAID upgrade board is installed into the
system, it would be plugged into this slot if it is to control mainboard
SCSI device(s).
•
When a RAID upgrade card is not installed, interrupts from a SCSI
core must not be presented to the system’s interrupt controller using
multiple interrupt inputs.
The LSI53C895A supports four different interrupt routing modes.
Additional information for these modes may be found in the
Register 0x4D
description in
The interrupt routing mode is selected using bits [1:0] in the
STEST1 register. Mode 0 is the default mode and is compatible with AMI
RAID upgrade products. In this mode, interrupts are presented on IRQ/
and ALR_IRQ/.
If INTB/, INTC/ or INTD/ of the PCI RAID upgrade slot is used in the
interrupt routing scheme, it cannot be used when a non-RAID upgrade
card is installed in the slot. If this restriction is not acceptable, additional
buffer logic must be implemented on the mainboard. As long as the
interrupt routing requirements stated above are satisfied, a mainboard
designer could implement this design with external logic.
There can only be one entity controlling a mainboard LSI53C895A or
conflicts will occur. Typically, SCSI BIOS and an operating system driver
control the LSI53C895A. When allocated to a RAID adapter, however, a
mechanism is implemented to prevent the SCSI BIOS and operating
system driver from trying to access the chip. The mainboard designer
has several options, listed below.
Summary of Contents for LSI53C895A
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