User`s guide

Adapter Specification

Overview

The Compaq VAX™-SCSI Wide Ultra SCSI Host is based on the LSI

53C875 SCSI controller chip. This chip includes the following:

•

Onboard RISC processor

•

Internal 512Byte FIFO

•

Internal 4Kbyte Script RAM

•

One interrupt per I/O scripts

IntraServer’s SCSI script implementation on the Symbios (LSI Logic)

53C875 SCSI processor offloads the CPU to deliver higher efficiency and

lower CPU utlization. All low level SCSI functions are completed by

SCRIPTS, which only interrupt the host when an I/O is complete. This

allows the SCSI interface to perform at a higher I/O rate than previous

implementations, which were limited by the processor’s ability to service

frequent interrupts.

Adapters designed for systems with a CDAL bus (Compaq adapters versions

DS-KZCCA-AB, -BB, -CB and -DB) interface directly to the CPU on the

CDAL bus, allowing for maximum I/O bandwidth possible for these systems.

Compaq’s DS-KZMCA-AB adapter (currently under development)

implements the XMI interface, and is intended to be used in XMI based

systems.

The high performance PCI SCSI core is interfaced to the system bus (CDAL

or XMI) by use of a Field Programmable Gate Array. The FPGA provides

arbitration for the PCI devices (SCSI and Ethernet are available options),

interrupt controll and data path.

Required Software

IntraServer’s PKW driver, a high performance Wide Ultra SCSI driver is

used as the port driver for the VAX-SCSI implementation. PKW is a port of

IntraServer’s PKWDRIVER which has been fully qualified by digital, and is

now part of the OpenVMS/Alpha distribution (V7.1-2 and V7.2). PKW

interfaces with the high performance scripts on the 53C875 to maximize

SCSI data throughput while minimizing CPU overhead.