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Case Studies

Dual SCSI Host Bus Adapter for EISA

Interphase Corporation’s E/SCSI 4810 Barracuda is the intelligent, high-performance SCSI (Small Com- puter System Interface) host bus adapter for 32-bit EISA (Extended Industry Standard Architecture) sys- tems requiring high data throughput and multiple drive storage.

The 4810 may be configured with one or two full function, fully independent SCSI channels, each support- ing up to seven SCSI peripherals. The 4810 features Interphase’s proven high-performance innovations, including BUSpacket Interface and Virtual Buffer Architectures, which give the 4810 unequalled perfor- mance in demanding high I/O per second and high data transfer rate applications such as file servers, database servers, and high-speed/high-resolution graphics.


The E/SCSI 4810 is derived from Interphase’s highly successful VMEbus SCSI host bus adapter, the V/SCSI 4210 Jaguar. Designed for the 40 Megabytes per second (MBytes/s) VMEbus, the Jaguar has a large and growing installed base that includes some of the highest performing VMEbus systems available in the industry today.


Interphase’s proven BUSpacket design has been adapted for the 4810’s EISA “Type C” 33 MBytes/s Burst DMA transfer mode. Type C is the maximum data transfer rate defined by the EISA specification.

BUSpacket uses a large RAM buffer coupled to a very fast and deep FIFO, which is in turn controlled by a hardware state machine. Packets of data are formatted and stored in the fast FIFO before they are burst over the EISA bus.


The 4810 Barracuda can be configured with one or two separate SCSI channels. The second SCSI channel can be factory or field installed, allowing the single slot Barracuda to support as many as 14 peripheral devices of various types, including magnetic or optical disk drives, tape drives and printers.

To optimize throughput in applications where performance is critical, system designers can divide a sys- tem’s I/O devices between the Barracuda’s two SCSI channels, with fast disk storage on one channel and slower backup devices on the second. This eliminates a potential bottleneck because the slower devices can require a larger-than-optimum percentage of the available SCSI bandwidth.

In addition, the Barracuda’s two SCSI buses can be used in mirroring or shadowing applications that require high data availability. Other fault tolerant configurations, high bandwidth striping applications or array configurations are possible because of the availability of two SCSI buses on a single host bus adapter.

MACSI (Multiple Active Command Software Interface)

Interphase’s second generation intelligent command queuing software interface, MACSI, was developed to give the OEM system integrator the flexibility to tailor the operation of the controller for the best pos- sible performance in a given application. The number of, size of, relative priority of, and operation of MACSI’s multi-level command queue interface are all under programmatic control. MACSI has been imple- mented and proven in many high-performance systems that use Interphase’s ESDI and SMD controllers and SCSI host bus adapters.


The E/SCSI 4810 Barracuda’s 68000 processor dynamically allocates sections of its 128 KByte buffer for use by the various tasks of the host adapter, optimizing the sizes of the various buffers depending upon the operation in progress. This sophisticated approach to buffer management insures sufficient buffer space for multithreaded read/write transactions to run efficiently. Read overruns and write underruns often experienced in less sophisticated FIFO-based or fixed allocation RAM designs are avoided by Barra- cuda’s ability to adapt as conditions change.


The E/SCSI 4810 Barracuda accommodates virtually any type of SCSI peripheral, including magnetic and optical disk drives, half-inch and quarter-inch tape transports and printers. The Barracuda supports both asynchronous and the newer, higher performance synchronous SCSI devices. Additional flexibility is pro- vided by a printer daughter card that supports parallel interface printers.

The Need

A new Extended Industry Standard Architecture (EISA) bus computer market was defined by Compaq, Olivetti, AST, Hewlett Packard and others.  These computers were to be used for high speed file servers and workstations, and required new high speed disk, tape, and printer controllers.  Companies that built all new controllers would miss the market window.  

With the new controller, the new EISA computer was expected to handle 256 users instead of the original 45.


Our client had an asynchronous VME bus design already in production that had similar functions required by EISA.  A UNIX software driver and on-board firmware also existed.   The client required that any changes in the card allow it to use existing software as much as possible.

The client also required that the product be ready in time for an important trade show.  There was not enough time in the schedule to build a wire-wrap prototype.  Also, the target computer, which was based on the 80486 chip from Intel, would not be available until the very end of the project. 

The existing schematics were compiled on a Computer Aided Engineering (CAE) workstation, digital simulation was used, wave forms were plotted and analyzed, and corrections were made.   After modifications were made to the bus interface, a new synchronous state machine was implemented using programmable logic devices (PLD).  

A new section of 80486 code was added to the 68020 firmware, allowing the system to boot  from disk.

The final design was a 10-layer surface-mount and through-hole PCB design.   Dozens of circuit cards were manufactured and assembled, and preliminary testing was done while the anxious wait for the new EISA computer continued.