VMIVME-5576

Fiber-Optic Reflective Memory with Interrupts

High-speed, easy-to-use fiber-optic network (170 Mbaud serially)

Data written to memory in one node is also written to memory in all nodes on

the network

Up to 2.000 m between nodes and up to 256 nodes

Data transferred at 6.2 Mbyte/s without redundant transfer

Data transferred at 3.2 Mbyte/s with redundant transfer

Any node on the network can generate an interrupt in any other node on the

network or in all network nodes with a single command

Error detection

Redundant transmission mode for suppressing errors

No processor overhead

No processor involvement in the operation of the network

Up to 1 Mbyte of Reflective Memory

A24:A32:D32:D16:D8 memory access

Single 6U VMEbus board

INTRODUCTION

VMIVME-5576 is a

high-performance, multidrop VME-to-VME network. Data is

transferred by writing to on-board global RAM. The data is

automatically sent to the location in memory on all Reflective

Memory boards on the network.

PRODUCT OVERVIEW

—

The Reflective Memory

concept  provides a very fast and efficient way of sharing data

across distributed computer systems.

VMIC’s VMIVME-5576 Reflective Memory interface

allows data to be shared between up to 256 independent

systems (nodes) at rates up to 6.2 Mbyte/s. Each Reflective

Memory board may be configured with 256 Kbyte to 1 Mbyte

of on-board SRAM. The local SRAM provides fast Read

access times to stored data. Writes are stored in local SRAM

and broadcast over a high-speed fiber-optic data path to other

Reflective Memory nodes. The transfer of data between nodes

is software transparent, so no I/O overhead is required.

Transmit and Receive FIFOs buffer data during peak data

rates to optimize CPU and bus performance to maintain high

data throughput.

The Reflective Memory also allows interrupts to one or

more nodes by writing to a byte register. These interrupt (three

level, user definable) signals may be used to synchronize a

system process, or used to follow any data that may have

preceded it. The interrupt always follows the data to ensure the

reception of the data before the interrupt is acknowledged.

The VMIVME-5576 requires no initialization unless

interrupts are being used. If interrupts are used, vectors and

interrupt levels must be written to on-board registers and the

interrupts armed.

Each node on the system has a unique identification

number between 0 and 255. The node number is established

during hardware system integration by placement of jumpers

on the board. This node number can be read by software by

accessing an on-board register. In some applications, this node

number would be useful in establishing the function of the

node.

LINK ARBITRATION — The VMIVME-5576 system

is a fiber-optic daisy chain ring as shown in Figure 2. Each

transfer is passed from node to node until it has gone all the

way around the ring and reaches the originating node. Each

node retransmits all transfers that it receives except those that

it had originated. Nodes are allowed to insert transfers

between transfers passing through.

INTERRUPT TRANSFERS — In addition to

transferring data between nodes, the VMIVME-5576 will

allow any processor in any node to generate an interrupt on

any other node. These interrupts would generally be used to

indicate to the receiving node that new data has been sent and

is ready for processing. These interrupts are also used to

indicate that processing of old data is completed and the

receiving node is ready for new data.

Three interrupts are available. The user may define the

function, priority, and vector for each interrupt. Any

processor can generate an interrupt on any other node on the

network. In addition, any processor on the network can

generate an interrupt on all nodes on the network. Interrupts

are generated by simply writing to a single VMIVME-5576

register.

All data and interrupt command transfers contain the

node number of the node that originated the transfer. This

information is used primarily so the originating node can

remove the transfer from the network after the transfer has

traversed the ring. The node identification is also used by

nodes receiving interrupt commands. When a node receives

an interrupt command for itself, it places the identification

number of the originating node in a FIFO. Up to 512

interrupts can be stacked in the FIFO. During the interrupt

service routine, the identification of the interrupting node can

be read from the FIFO.

ERROR MANAGEMENT — Errors are detected by

the VMIVME-5576 with the use of the error detection

facilities of the TAXI chipset and additional parity encoding

and checking.  The error rate of the VMIVME-5576 is a

function of the rate of errors produced in the optical portion

of the system.  This optical error rate depends on the length

and type of fiber-optic cable.

Assuming an optical error rate of 10-12. the error rate of

the VMIVME-5576 is 10-10 transfers/transfer. However, the

rate of undetectable errors is less than 10-20 transfers/transfer.

When a node detects an error, the erroneous transfer is

removed from the system and a VMEbus interrupt is

generated, if armed.

The VMIVME-5576 can be operated in a redundant

transfer mode in which each transfer is transmitted twice. In

this mode of operation, the first of the two transfers is used

unless an error is detected in which case the second transfer

is used. In the event that an error is detected in both transfers,

the node removes the transfer from the system. The

probability of both transfers containing an error is 10-20. or

about one error every 372.000 years at maximum data rate.

PROTECTION AGAINST LOST DATA — Data

received by the node from the fiber-optic cable is error

checked and placed in a receive FIFO.  Arbitration with

accesses from the VMEbus then takes place and the data is

written to the node’s SRAM and to the node’s transmit FIFO.

Data written to the board from the VMEbus is placed directly

into SRAM and into the transmit FIFO.  Data in the transmit

FIFO is transmitted by the node over the fiber-optic cable to

the next node.  Data could be lost if either FIFO were allowed

to become full.

The product is designed to prevent either FIFO becoming

full and overflowing. It is important to note the only way that

data can start to accumulate in FIFOs is for data to enter the

node at a rate greater than 6.2 or 3.2 Mbyte/s in redundant

mode. Since data can enter from the fiber and from the

VMEbus, it is possible to exceed these rates. If the transmit

FIFO becomes half-full, a bit in the Status Register is set and,

if armed, an interrupt is generated. This condition is an

indication to the software in the node that writes to the

Reflective Memory should be suspended until the FIFO

becomes less than half-full. If the half-full indication is

ignored and the transmit FIFO becomes full, then writes to the

Reflective Memory will be acknowledged with a bus error.

With VMEbus writes being blocked by the bus error, data

cannot overflow in the receive FIFO.

NETWORK MONITOR — There is a bit in a Status

Register that can be used to verify that data is traversing the

ring (that is, the ring is not broken). This can also be used to

measure network latency.

SPECIFICATIONS

Memory Size: 256 Kbyte, 512 Kbyte, or 1 Mbyte

Access Time:

400 ns (worst-case arbitration)

200 ns (best-case arbitration)

TRANSFER SPECIFICATION

Transfer Rate:

6.2 Mbyte/s (longword accesses) without redundant

transfer

3.2 Mbyte/s (longword accesses) with redundant transfer

COMPATIBILITY

VMEbus: This product complies with the VMEbus

specification (ANSI/IEEE STD 1014-1987. IEC 821 and

297), with the following mnemonics:

A32: A24: D32/D16/D08 (EO): Slave: 39/3D:09/0D

Form factor: 6U

Memory: Addressable on 256 Kbyte boundaries for

256 Kbyte memory option

Addressable on 512 Kbyte boundaries for 512 Kbyte

memory option

Addressable on 1 Mbyte boundary for 1 Mbyte memory

option

INTERCONNECTION

Cable Requirements: Two fiber-optic cables

Cable Length: 2.000 m maximum between nodes

Configuration: Daisy chain ring up to 256 nodes

PHYSICAL/ENVIRONMENTAL

Temperature Range: 0 to 55 °C, operating-40 to 85 °C, storage

Relative Humidity: 20 to 80 percent, noncondensing

Power Requirements: 5.0 A maximum at +5 VDC

MTBF: 142.400 hours (217F)

DATA TRANSFERS

Data written into the Reflective Memory is broadcast to

all nodes on the network without further involvement of the

sending or receiving nodes.  Data is transferred from memory

locations on the sending nodes to corresponding memory

locations on the receiving nodes.

A functional block diagram of the VMIVME-5576 is

shown in Figure 1.

TRADEMARKS

The VMIC logo is a registered trademark of VMIC.

Other registered trademarks are the property of their

respective owners.