Avago Technologies LSI53C896 - Manual (Page 48)

2-20 Functional Description
Version 3.3 Copyright © 1998–2003 by LSI Logic Corporation. All rights reserved.
signal on the SCSI bus is used in error recovery and diagnostic
procedures. In support of SCSI loopback diagnostics, each SCSI function
may perform a self-selection and operate as both an initiator and a target.
The LSI53C896 is controlled by the integrated SCRIPTS processor
through a high-level logical interface. Commands controlling the SCSI
functions are fetched out of the main host memory or local memory.
These commands instruct the SCSI functions to Select, Reselect,
Disconnect, Wait for a Disconnect, Transfer Information,
Change Bus Phases and, in general, implement all aspects of the SCSI
protocol. The SCRIPTS processor is a special high-speed processor
optimized for SCSI protocol.
2.2.1 SCRIPTS Processor
The SCSI SCRIPTS processor allows both DMA and SCSI commands
to be fetched from host memory or internal SCRIPTS RAM. Algorithms
written in SCSI SCRIPTS control the actions of the SCSI and DMA
cores. The SCRIPTS processor executes complex SCSI bus sequences
independently of the host CPU.
Algorithms may be designed to tune SCSI bus performance, to adjust to
new bus device types (such as scanners and communication gateways),
or to incorporate changes in the SCSI-2 or SCSI-3 logical bus definitions
without sacrificing I/O performance. SCSI SCRIPTS are hardware
independent, so they can be used interchangeably on any host or CPU
system bus. SCSI SCRIPTS also handle conditions such as
Phase Mismatch.
Phase Mismatch Handling in SCRIPTS – The LSI53C896 can handle
phase mismatches due to drive disconnects without needing to interrupt
the processor. The primary goal of this logic is to eliminate the need for
CPU intervention during an I/O disconnect/reselect sequence.
Storing the appropriate information to restart the I/O later can be done
through SCRIPTS, eliminating the need for processor intervention during
an I/O disconnect/reselect sequence. Calculations are performed such
that the appropriate information is available to SCRIPTS so that an I/O
state can be properly stored for restart later.