Browse Prior Art Database

Diagnostic Wrap Mode for System Interface

IP.com Disclosure Number: IPCOM000044669D
Original Publication Date: 1984-Dec-01
Included in the Prior Art Database: 2005-Feb-06
Document File: 2 page(s) / 55K

Publishing Venue

IBM

Related People

Preston, DC: AUTHOR

Abstract

The diagnostic wrap mode for system interface provides the processor with the ability to analyze a system bus interface and logic lines feeding it, without using a second bus unit. The wrap mode is a method of sending data, present at the input, of the system bus drivers back to the communication register, to allow the bus subunit to test itself, up to the point that the data goes on to the bus without actually putting the data on the bus. The four bytes directly on the system bus 12 make this wrapping possible. By adding some logic to the set condition, the communication register 13 can be used to latch both the external data bus 14 and the address bus 15 that feed the system bus multiplexer 16.

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Diagnostic Wrap Mode for System Interface

The diagnostic wrap mode for system interface provides the processor with the ability to analyze a system bus interface and logic lines feeding it, without using a second bus unit. The wrap mode is a method of sending data, present at the input, of the system bus drivers back to the communication register, to allow the bus subunit to test itself, up to the point that the data goes on to the bus without actually putting the data on the bus. The four bytes directly on the system bus 12 make this wrapping possible. By adding some logic to the set condition, the communication register 13 can be used to latch both the external data bus 14 and the address bus 15 that feed the system bus multiplexer 16. Being able to latch either of these buses allows the analysis of their condition up to the point that they enter the system bus 12 and this allows a full understanding of the condition of these lines before using them in a bus cycle directed to another subunit. The directory look-aside table (DLAT) 17 portion of the address data flow does not have the ability to latch the translated real address it supplies to multiplexer 16. By putting the communication register 13 in wrap mode and performing a memory read, the translated address can be latched up exactly as it appears on system bus 12, allowing a full test of the DLAT 17 without sending the address and command across the system bus 12 to storage. This diagnostic wrap mode thus...