Browse Prior Art Database

TAG TRANSITION METHOD for INTERLOCKED BUS OPERATION

IP.com Disclosure Number: IPCOM000039986D
Original Publication Date: 1987-Sep-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 4 page(s) / 43K

Publishing Venue

IBM

Related People

Bourke, DG: AUTHOR [+2]

Abstract

This article describes a method for achieving interlocked information transfers on asynchronous busses with increased speed of operation and applicability to repowered and unrepowered environments. The method disclosed herein is most suited to packet busses, a type of bus that is markedly superior in repowered environments. Fig. 1 is a general diagram of a bus. For purposes of this description, there are two types of units that may reside on a bus. Bus Unit (BU) - Bus Units participate actively in bus operations. During an operation, a pair of units exchange information. Repower Unit (RU) - Repower Units are normally transparent to bus operations. They have a threefold function: 1. Redrive - Refreshing bus signals to appropriate drive levels. (Image Omitted) 2.

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TAG TRANSITION METHOD for INTERLOCKED BUS OPERATION

This article describes a method for achieving interlocked information transfers on asynchronous busses with increased speed of operation and applicability to repowered and unrepowered environments. The method disclosed herein is most suited to packet busses, a type of bus that is markedly superior in repowered environments. Fig. 1 is a general diagram of a bus. For purposes of this description, there are two types of units that may reside on a bus. Bus Unit (BU) - Bus Units participate actively in bus operations. During an operation, a pair of units exchange information. Repower Unit (RU) - Repower Units are normally transparent to bus operations. They have a threefold function:

1. Redrive - Refreshing bus signals to appropriate drive levels.

(Image Omitted)

2. Deskewing -

Introducing appropriate delays between tag sig nals and the busses that they validate. 3. Steering - Establishing the direction of bus lines between

communicating Bus Units. BUs are shown multidropped and RUs as series elements for bus lines. Bus lines are repowered through bidirectional driver pairs in RUs. A bus section between two RUs is termed a segment. It is sufficient to define three types of bus lines: - Information Bus - A group of lines used to convey information from the unit driving the bus to the unit receiving the

information. Usually the information is data, but the bus

could have multiplexed use to convey commands or addresses. - Bus Driver Tag (DRVR) - This tag is driven by the BU that is driving the Information Bus. It has conventional bus valida-

tion use. - Response Tag (RESP) - This tag is driven by the receiver of the Information Bus contents.

(Image Omitted)

Interlocked bus transfers are an accepted means of conveying information on asynchronous busses, since they ensure freedom from dissimilar delays introduced by BUs having separate clocks and potentially different technologies. An interlocked bus operation is a bus operation where the driver of the Information Bus transfers the contents of the Information Bus at the pace of the receiver. Interlocking is achieved by allowing changes in the level of the driving unit's tag only if that change is acknowledged by the receiving unit. It is also commonly called "handshaking". A bus operation is the smallest unit of communication between two

1

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particular bus units before the bus must be given up for re-arbitration. Bus operations, especially on contemporary busses, usually incorporate multiple information transfers, or multiple bus cycles on a given operation. Also, because information-conveying busses have become wider, designs have tended toward multiplexed use of a single bus to convey commands, addresses, and data during an operation. Busses incorporating such design notions are called "packet" busses. Figs. 2 and 3 contrast the tag transition method for interlocking transfers with conventional methods. A four-cycle operation i...