Avago Technologies LSI53C1000R - Manual (Page 49)

SCSI Functional Description 2-19
Version 2.2 Copyright © 2000–2003 by LSI Logic Corporation. All rights reserved.
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, communication gateways, etc.
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 LSI53C1000R can
handle phase mismatches due to drive disconnects without needing to
interrupt the processor. The primary goal of this logic is to completely
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.
The Phase Mismatch Jump logic is disabled at power-up. To enable the
phase mismatch jump logic, set the Phase Mismatch Jump Enable bit
(ENPMJ, bit 7 in the
Chip Control Zero (CCNTL0) register). Utilizing the
information supplied in the Phase Mismatch Jump Address registers
allows all overhead involved in a disconnect/reselect sequence to be
handled with a modest amount of SCRIPTS instructions. These registers
are described in detail in
Chapter 4, “Registers.”