
2-48
Functional Description
4.
If only the DIP bit is set, read
DMA Status (DSTAT)
to clear the
interrupt condition and get the DMA interrupt status. The bits in
DSTAT tell which DMA interrupts occurred and determine what action
is required to service the interrupts.
5.
If both the SIP and DIP bits are set, read
SCSI Interrupt Status Zero
(SIST0)
,
SCSI Interrupt Status One (SIST1)
, and
DMA Status (DSTAT)
to clear the SCSI and DMA interrupt condition and get the interrupt
status. If using 8-bit reads of the SIST0, SIST1, and DSTAT registers
to clear interrupts, insert a 12 clock delay between the consecutive
reads to ensure that the interrupts clear properly. Both the SCSI and
DMA interrupt conditions should be handled before leaving the
Interrupt Service Routine. It is recommended that the DMA interrupt
is serviced before the SCSI interrupt, because a serious DMA
interrupt condition could influence how the SCSI interrupt is acted
upon.
6.
When using polled interrupts go back to step 1 before leaving the
interrupt service routine in case any stacked interrupts moved in
when the first interrupt was cleared. When using hardware interrupts,
the INTA/ (or INTB/) pin is asserted again if there are any stacked
interrupts. This should cause the system to re-enter the interrupt
service routine.
2.2.17 Interrupt Routing
This section documents the recommended approach to RAID ready
interrupt routing for the SYM53C896. In order to be compatible with AMI
RAID upgrade products and the SYM53C896, the following requirements
must be met:
When a RAID upgrade card is installed in the upgrade slot, interrupts
from the motherboard SCSI controller(s) assigned to the RAID
upgrade card must be routed to INTC/ and INTD/ of the upgrade slot
and isolated from the motherboard 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 motherboard 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
motherboard SCSI device(s).