Browse Prior Art Database

9370 SPD I/O Bus Extension Features

IP.com Disclosure Number: IPCOM000035159D
Original Publication Date: 1989-Jun-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 7 page(s) / 144K

Publishing Venue

IBM

Related People

Kelley, RA: AUTHOR [+2]

Abstract

Extending the 9370 SPD I/O Bus into I/O Expansion Modules for the purpose of attaching more I/O devices to be contained within the processor is accomplished by a Bus Extension Unit (BEU) which extends the functions of the BEU into the I/0 Expansion Module. The BEU consists of a pair of logic cards interconnected by a cable. The card in the pair nearer the Bus Control Unit (BCU) is referred to as the primary BEU card and the other card as the secondary BEU card, as shown in Fig. 1.

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9370 SPD I/O Bus Extension Features

Extending the 9370 SPD I/O Bus into I/O Expansion Modules for the purpose of attaching more I/O devices to be contained within the processor is accomplished by a Bus Extension Unit (BEU) which extends the functions of the BEU into the I/0 Expansion Module. The BEU consists of a pair of logic cards interconnected by a cable. The card in the pair nearer the Bus Control Unit (BCU) is referred to as the primary BEU card and the other card as the secondary BEU card, as shown in Fig. 1.

Bits 29-31 of the address/data bus define the board address for Direct Select operations. When the BCU decodes bits 29-31 as zero, it drives Board Select, as defined in [*]. Binary values of one through seven are intended to identify extension board addresses for direct selection. This function is initialized by the BCU by assigning a unique board address to each primary BEU card in a system.

When the three bit board address in the primary BEU card is non- zero and equivalent to bits 29-31 of the address bus, Board Select is issued to the secondary BEU via the cable. The secondary BEU drives the Board Select signal in its board to the state of the cable board select. The Board Select and Card Select signals are used by IOBUs on the extension board for Direct Selection as described in [*].

Following system Power-on and Unit Reset commands, IOBUs do not have an assigned IOBU address and cannot participate in Address Selected unit or storage operations. Addresses must be assigned via Direct Select commands from the BCU. The BEU supports Direct Selection on extension boards.

Because of the way the BEU controls bus and tag steering, peer-to- peer operations are supported betwen all IOBUs, regardless of their relative location on any of the boards on a bus.

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Slave storage operations are supported by the BEU. Each BEU monitors arbitration, tracking the location of the master. Having determined the relative location of the master, information necessary for selection as a slave is steered away from the master in both directions, such that an IOBU at any location may be selected as slave. This function is supported by the BEUs for both Unit and Storage operations.

Status information is collected by the BCU to support fault isolation and error recovery. The status collected is adequate for isolating faults on the processor board, but cannot provide information necessary for fault isolation on extension boards.

The BEU provides two important features to enhance fault isolation when multiple boards are involved. The first feature is an extension of the status collected by the BCU. Each primary and secondary BEU collects information

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similar to that collected by the BCU in the Monitor Status Word. This allows the system to isolate faults occurring on any board in the system.

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The second feature prohibits failing IOBUs on outlying boards from interfering with operations on preceding boards....