Avago Technologies LSI53C1010 - Manual (Page 220)

9-22 SCRIPTS Programming Topics
9.5.2.7 DCNTL (All chips except the LSI53C770, LSI53C810, LSI53C815, and
LSI53C860)
When bit 1 in this register is set, the IRQ/ pin is not asserted when an
interrupt condition occurs. The interrupt is not lost or ignored, but merely
masked at the pin. Clearing this bit when an interrupt is pending
immediately asserts the IRQ/ pin. As with any register other than ISTAT,
this register cannot be accessed except by a SCRIPTS instruction during
SCRIPTS execution.
9.5.3 Fatal vs. Nonfatal Interrupts
A fatal interrupt, as the name implies, always stops SCRIPTS execution.
All nonfatal interrupts become fatal when they are enabled by setting the
appropriate interrupt enable bit. All DMA interrupts are fatal. Interrupt
masking is discussed in
Section 9.5.4, “Masking.”
Some SCSI interrupts, as indicated by the SIP bit in the ISTAT register
and one or more bits in the SIST0 or SIST1 register being set, are
nonfatal. When the SCRIPTS processor is operating in the Initiator Mode,
only the Function Complete (CMP), Selected (SEL), Reselected (RSL),
General Purpose Timer Expired (GEN), and Handshake-to-Handshake
Timer Expired (HTH) interrupts are nonfatal. When operating in the
Target Mode, CMP, SEL, RSL, Target Mode: SATN/ active (M/A), GEN,
and HTH are nonfatal. Refer to the description for the Disable Halt on a
Parity Error or SATN/ active (Target Mode only) (DHP) bit in the SCNTL1
register to configure the chip’s behavior when the SATN/ interrupt is
enabled during Target Mode operation. The Interrupt on the Fly interrupt
is also nonfatal, since SCRIPTS can continue when it occurs.
Nonfatal interrupts allow continued SCRIPTS operation when an interrupt
occurs that does not require service from the CPU. This prevents an
interrupt when:
•
Arbitration is complete (CMP set)
•
The SCRIPTS processor has been selected or reselected (SEL or
RSL set)
•
The initiator has asserted SATN/ (Target Mode: SATN/ active)
•
General Purpose or Handshake-to-Handshake timers expire