2-50
Functional Description
Setting the SIRQD bit in the
register
disables the interrupt pin for the SCSI function. If an interrupt pin is
already asserted and SIRQD is then set, the interrupt pin will remain
asserted until serviced. Further interrupts will be blocked from the
interrupt pin.
When the LSI53C1000 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/ pin.
2.2.16.5 Stacked Interrupts
The LSI53C1000 stacks 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. 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 later interrupts move
into SIST0, SIST1, and DSTAT. After the first interrupt is cleared, the
INTA/ pin is deasserted for a minimum of three CLKs; the stacked
interrupts move into SIST0, SIST1, or DSTAT; and the INTA/ pin is
asserted once again.
Since a masked nonfatal interrupt does not set the SIP or DIP bits,
interrupt stacking does not occur. A masked, nonfatal interrupt still posts
the interrupt in
SCSI Interrupt Status Zero (SIST0)
, but does not assert
the INTA/ pin. Since no interrupt is generated, future interrupts move into
SCSI Interrupt Status Zero (SIST0)
or
SCSI Interrupt Status One (SIST1)
instead of stacking behind another interrupt. When another interrupt
condition occurs, the bit corresponding to the earlier masked nonfatal
interrupt is set.
Содержание LSI53C1000
Страница 6: ...vi Preface...
Страница 16: ...xvi Contents...
Страница 28: ...1 12 Introduction...
Страница 234: ...4 124 Registers...
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Страница 350: ...6 76 Specifications Figure 6 42 LSI53C1000 329 Ball Grid Array Bottom view...
Страница 352: ...6 78 Specifications...
Страница 360: ...A 8 Register Summary...
Страница 376: ...IX 12 Index...