User`s manual

Functional Overview
SBCSCSI/D1 2-9
2
SCSI Gross Error
This interrupt is generated when the SIOP detects an illegal
condition in the SIOP bus control logic (e.g., an overflow of
the SCSI FIFO) or and illegal condition on the SCSI bus (e.g.,
a phase change with an outstanding synchronous offset). The
Firmware hangs if this interrupt occurs.
INT Instruction
This is the SCRIPTS programmed interrupt invoked by the
INT instruction. Programmed interrupts cause the MPU code
to handle situations which the SCRIPTS or SIOP cannot.
Illegal Instruction
This interrupt is generated when the SIOP attempts to execute
an illegal SCRIPTS instruction. Several different situations
can produce an illegal SCRIPTS instruction. The Firmware
determines the specific reason for the illegal instruction. The
Firmware gets the current target off the bus before
terminating the command and returning status to the user.
These are some of the reasons for an illegal instruction.
1. The NCR SCRIPTS compiler generated the wrong opcode
for a SCRIPTS instruction forcing the SIOP to execute an
illegal opcode.
2. The memory where the SCRIPTS reside has been
corrupted. This results in the SIOP executing an illegal
opcode.
3. The SIOP attempts to execute a SCRIPTS instruction
which is non-longword (four-byte) aligned. All SCRIPTS
must be aligned to byte boundaries that are integer
multiples of 4.
4. The SIOP attempts to transfer information but has been
supplied with a transfer count of zero. This could occur if
the user built an siop_struc to execute a SCSI read but
initialized the data_count Þeld to zero.
Bus Fault This interrupt is generated whenever the SIOP receives a bus
error in response to a local bus access. Action by the
Firmware is dependent upon the current phase of the SCSI
bus.