Avago Technologies LSI53C1010R - Manual (Page 49)

SCSI Functional Description 2-19
Version 2.2 Copyright © 2000–2003 by LSI Logic Corporation. All rights reserved.
The LSI53C1010R offers low level register access or a high level control
interface. Like first generation SCSI devices, the LSI53C1010R is
accessed as a register-oriented device. The ability to sample and/or
assert any signal on the SCSI bus is used in error recovery and
diagnostic procedures.
The LSI53C1010R 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
implement all other 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 fetches of both DMA and SCSI
commands from host memory or internal SCRIPTS RAM. Algorithms
written in SCSI SCRIPTS control the actions of the SCSI and DMA
cores. The SCRIPTS processor, running off of the PCI clock, executes
complex SCSI bus sequences independently of the host CPU.
Algorithms can be designed to tune SCSI bus performance to adjust to
new bus device types such as scanners and communication gateways.
They can also incorporate changes in the SCSI 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 handle conditions such as Phase Mismatch.
Phase Mismatch Handling in SCRIPTS – The LSI53C1010R 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.
SCRIPTS control the storage of appropriate information needed to
restart the I/O state, 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.