Latest Alpha Processor Performance Available on VME

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by Jon Crowell, Engineering Manager
Embedded and Realtime Products Group
Digital Equipment Corporation

In designing Digital Alpha VME 4/224 and 4/288 single board VME computers to meet the demands of the high performance embedded and realtime markets, the goals were to bring the performance and reliability of AlphaServer and AlphaStation systems into the form factor of a 6U x 160mm VME module. The result is a high performance Alpha system on a module that comfortably fits in a standard VME backplane. The product is produced in two CPU speed variants, 224 and 288 Mhz. The 288 MHz product will yield over 200 SPECin92(est.) and 250 SPECfp92 (est.). This CPU design uses the same core logic found in Digtial's AlphaServer 1000 system.
The modules are supported by the Digital-UNIX operating system and the VxWorks (tm) for Alpha operating system from Wind River Systems, Inc.
Design Goals
The primary goal of the project was to place the compute and I/O performance of the latest Alpha processors onto a VME 6U x 160mm module. This design puts the Alpha 21064A CPU on the VME bus and provides the physical design to support the 21164 processor in the next generation module design. The main project goals are listed below:

· Provide a module packaging scheme that will reliably support all future generations of the Alpha CPU chips.
· Provide high performance ECC memory. Initial support for at least 128MB of memory, using JEDEC (x80) DIMM memory modules.
· Provide design features that will allow the CPU and IO functionality to be upgraded as improvements are made in either area.
· Produce two module variations for each CPU generation. One to be performance focused using the fastest Alpha chips possible in this package and the other more cost focused.
· Provide a design that can be powered and cooled in a standard 5V VME system enclosure.
· Provide support for high performance onboard I/O as well as PCI expansion via PCI Mezzanine (PMC) slots.
Module Functionality
The first two members of the new Alpha VME family are based on the Alpha 21064A CPU chip. This processor is based on a 0.5u CMOS process and operates at cycle clock frequencies up to 288MHz.
The processor is capable of retrieving up to two instructions each clock cycle, yielding a peak instruction rate of 576,000,000 instructions per second. The CPU chip has 32K bytes of direct mapped write-through primary cache on chip to help keep the processor from stalling as well as up to 2MB of external cache.
The design is portioned into a base CPU module and an I/O daughter card. The 21064A base module design has the following functions:

· Alpha 21064A CPU chip
· Connectors for Backup cache
· Memory controller (128 Bit wide data w/ ECC)
· Connectors for two banks of Memory
· PCI bus adapter logic (32 bit wide bus)
· Clock generation
· DC to DC power conversion

The first generation I/O card is irregularly shaped to allow some of the components from the base module to consume two slots. The I/O card connects to the CPU base module via a controlled impedance connector that carries the PCI bus as well as other required system signals. The I/O card has the following functions:

· PCI-to-VME bridge supporting VME64
· SCSI-2 Adapter
· Ethernet adapter (10baseT)
· TOY clock with 32KB of NVRAM
· Two ASYNC serial lines · Three real time timers
· 4MB of flash ROM
· Parallel port
· Keyboard and Mouse controller

The PCI expansion is provided via an optional module. In its first implementation this module provides support for two single PMC option cards or one dual PMC card. A VME breakout module provides connection to the SCSI bus, parallel port, keyboard and mouse.
The physical design of all modules was structured to consider support for the next generation Alpha 21164A CPU chip. It is a goal for this next generation CPU module to be compatible with the current I/O and breakout modules.
Design Details
The CPU uses a high performance memory subsystem providing memory configurations from 16 to 128MB using 16Mb DRAM technology. The base module supports two banks of memory based on pairs of JEDEC x80 DIMM memory modules. Each memory bank is 128 bits wide (plus ECC) and provides 16 bytes of data with each memory clock.
The backup cache is designed using custom static RAM modules. This allows support for either a 512KB or 2MB cache. The cache is error correcting with a 128bit data path to the CPU. This allows an application to only pay for the cache that is required to meet the performance requirements.
The first generation I/O module was designed to be upgradeable as new functionality is offered. The VME bus is driven from this I/O module via the PCI to VME adapter. The I/O module also makes the connection to the optional PCI expansion module. It is a goal for future CPU modules to remain compatible with this I/O module, thus reducing upgrade costs.
The reliability of any complex CPU design is dominated by the timing margins and signal integrity. The CPU core logic design used as the basis of the Alpha VME 4 design is identical to that used on other Digital AlphaServer and AlphaStation designs. This core logic design has been proven again and again in other of Digital's 21064A based designs.
When adopting this design, significant engineering effort was taken to design the rules required for high margin, low noise printed circuit board layout. These rules were used to drive a sophisticated rules based circuit board router. The result is a design with outstanding signal integrity in the first pass design. Another by-product of good signal integrity is lower RFI emissions from the module in actual systems.
Another challenge of the design was to fit it in this very compact area of a 6u x 160mm module. This forced us to use many parts in more compact packages. These included very small footprint surface mount resistors and capacitors to VME transverse in smaller packages. The resulting design fits comfortably in the form factor, is easy to manufacture, and has room to grow both with newer faster Alpha CPU chips as well as enhancements to it's I/O capabilities.
Summary
The packaging design done for this generation of the Alpha VME products has positioned us to introduce new products very quickly.
Digital is working to introduce new members of the Alpha VME family soon after the CPU chips appear in AlphaServers. As the new product family rolls out we will be firmly positioned to have the fastest VME single board computers providing access to commercial world class operating systems and tools. As this generation of product has more than doubled the CPU performance of our current top end Alpha VME 230 product, we plan to continue to stay ahead of the performance curve with the next generation of product we introduce.

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