LSI53C875 LSI Logic, LSI53C875 Datasheet - Page 53

• Manufacturer Part Number: LSI53C875
• Description: PCI to Ultra SCSI I/O Processor
• Manufacturer: LSI Logic

a hardware interrupt. The INTF (Interrupt-on-the-Fly) bit should be the
first interrupt serviced. It must be written to one to be cleared. This
interrupt must be cleared before servicing any other interrupts.
If the SIP bit in the
Interrupt Status (ISTAT)
register is set, then a
SCSI-type interrupt has occurred and the
SCSI Interrupt Status Zero
(SIST0)
and
SCSI Interrupt Status One (SIST1)
registers should be read.
If the DIP bit in the
Interrupt Status (ISTAT)
register is set, then a
DMA-type interrupt has occurred and the
DMA Status (DSTAT)
register
should be read.
SCSI-type and DMA-type interrupts may occur simultaneously, so in
some cases both SIP and DIP may be set.
SIST0 and SIST1 – The
SCSI Interrupt Status Zero (SIST0)
and
SCSI
Interrupt Status One (SIST1)
registers contain the SCSI-type interrupt
bits. Reading these registers determines which condition or conditions
caused the SCSI-type interrupt, and clears that SCSI interrupt condition.
If the LSI53C875 is receiving data from the SCSI bus and a fatal interrupt
condition occurs, the chip attempts to send the contents of the DMA
FIFO to memory before generating the interrupt.
If the LSI53C875 is sending data to the SCSI bus and a fatal SCSI
interrupt condition occurs, data could be left in the DMA FIFO. Because
of this, the DMA FIFO Empty (DFE) bit in
DMA Status (DSTAT)
should
be checked.
If this bit is cleared, set the CLF (Clear DMA FIFO) and CSF (Clear SCSI
FIFO) bits before continuing. The CLF bit is bit 2 in
Chip Test Three
(CTEST3). The CSF bit is bit 1 in
SCSI Test Three
(STEST3).
DSTAT – The
DMA Status (DSTAT)
register contains the DMA-type
interrupt bits. Reading this register determines which condition or
conditions caused the DMA-type interrupt, and clears that DMA interrupt
condition. Bit 7 in DSTAT, DFE, is purely a status bit; it will not generate
an interrupt under any circumstances and will not be cleared when read.
DMA interrupts flush neither the DMA nor SCSI FIFOs before generating
the interrupt, so the DFE bit in the
DMA Status (DSTAT)
register should
be checked after any DMA interrupt.
PCI Cache Mode
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