2 high level scsi scripts mode – Avago Technologies LSI53C876E User Manual
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5-2
SCSI SCRIPTS Instruction Set
5.2 High Level SCSI SCRIPTS Mode
To operate in the SCSI SCRIPTS mode, the LSI53C876 requires only a
SCRIPTS start address. The start address must be at a Dword (four
byte) boundary. This aligns subsequent SCRIPTS at a Dword boundary
since all SCRIPTS are 8 or 12 bytes long. Instructions are fetched until
an interrupt instruction is encountered, or until an unexpected event
(such as a hardware error) causes an interrupt to the external processor.
Once an interrupt is generated, the LSI53C876 halts all operations until
the interrupt is serviced. Then, the start address of the next SCRIPTS
instruction is written to the
register to
restart the automatic fetching and execution of instructions.
The SCSI SCRIPTS mode of execution allows the LSI53C876 to make
decisions based on the status of the SCSI bus, which offloads the
microprocessor from servicing the numerous interrupts inherent in I/O
operations.
Given the rich set of SCSI oriented features included in the instruction
set, and the ability to re-enter the SCSI algorithm at any point, this high
level interface is all that is required for both normal and exception
conditions. Switching to low level mode for error recovery is not required.
The following types of SCRIPTS instructions are implemented in the
LSI53C876 as shown in