Avago Technologies LSI53C896 User Manual
Page 77
SCSI Functional Description
2-49
Version 3.3
Copyright © 1998–2003 by LSI Logic Corporation. All rights reserved.
2.2.17.7 Sample Interrupt Service Routine
The following is a sample of an interrupt service routine for the
LSI53C896. It can be repeated if polling is used, or should be called
when the INTA/ (or INTB/) pin is asserted if hardware interrupts are used.
1.
Read
Interrupt Status Zero (ISTAT0)
2.
If the INTF bit is set, it must be written to a one to clear this status.
3.
If only the SIP bit is set, read
SCSI Interrupt Status Zero (SIST0)
and
SCSI Interrupt Status One (SIST1)
to clear the SCSI interrupt
condition and get the SCSI interrupt status. The bits in the SIST0
and SIST1 tell which SCSI interrupts occurred and determine what
action is required to service the interrupts.
4.
If only the DIP bit is set, read
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
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.