SCSI Functional Description
2-47
If a fatal interrupt is masked and that condition occurs, then the SCRIPTS
still stop, the appropriate bit in the
,
, or
SCSI Interrupt Status One (SIST1)
register is
set, and the SIP or DIP bit in the
Interrupt Status Zero (ISTAT0)
register
is set, but the INTA/ (or INTB/) pin is not asserted.
Interrupts can be disabled by setting the SYNC_IRQD bit in the
register. If an interrupt is already asserted and
SYNC_IRQD is then set, the interrupt will remain until serviced. Further
interrupts will be blocked.
When the LSI53C896 is initialized, enable all fatal interrupts if hardware
interrupts are being used. If a fatal interrupt is disabled and that interrupt
condition occurs, the SCRIPTS halts and the system never knows it
unless it times out and checks the
Interrupt Status Zero (ISTAT0)
, and
registers after a certain period of inactivity.
If ISTAT is being polled instead of using hardware interrupts, then
masking a fatal interrupt makes no difference since the SIP and DIP bits
in the
Interrupt Status Zero (ISTAT0)
inform the system of interrupts, not
the INTA/ (or INTB/) pin.
Masking an interrupt after INTA/ (or INTB/) is asserted does not cause
deassertion of INTA/ (or INTB/).
2.2.16.5 Stacked Interrupts
The LSI53C896 will stack interrupts, if they occur, one after the other. If
the SIP or DIP bits in the
Interrupt Status Zero (ISTAT0)
register are set
(first level), then there is already at least one pending interrupt, and any
future interrupts are stacked in extra registers behind the
SCSI Interrupt Status One (SIST1)
, and
registers (second level). When two interrupts have
occurred and the two levels of the stack are full, any further interrupts
set additional bits in the extra registers behind SIST0, SIST1, and DSTAT.
When the first level of interrupts are cleared, all the interrupts that came
in afterward move into SIST0, SIST1, and DSTAT. After the first interrupt
is cleared by reading the appropriate register, the INTA/ (or INTB/) pin is
deasserted for a minimum of three CLKs; the stacked interrupts move
into SIST0, SIST1, or DSTAT; and the INTA/ (or INTB/) pin is asserted
once again.
*
Summary of Contents for LSI53C896
Page 6: ...vi Preface...
Page 16: ...xvi Contents...
Page 88: ...2 62 Functional Description...
Page 112: ...3 24 Signal Descriptions...
Page 306: ...6 38 Specifications This page intentionally left blank...
Page 310: ...6 42 Specifications This page intentionally left blank...
Page 338: ...6 70 Specifications Figure 6 40 LSI53C896 329 BGA Bottom View...
Page 340: ...6 72 Specifications...
Page 346: ...A 6 Register Summary...
Page 362: ...IX 12 Index...