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DLAT Common Segment Multiple Compare Circuits

IP.com Disclosure Number: IPCOM000089305D
Original Publication Date: 1977-Oct-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 2 page(s) / 32K

Publishing Venue

IBM

Related People

Gannon, PM: AUTHOR [+2]

Abstract

In a virtual memory system, virtual addresses are translated to real addresses using sets of translation tables. A directory lookaside table (DLAT) which contains translation lookaside buffer (TLB) entries used for storing previously translated addresses so that they may be reused when the same virtual address is requested. This shortens the time for a processor to obtain most required data.

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DLAT Common Segment Multiple Compare Circuits

In a virtual memory system, virtual addresses are translated to real addresses using sets of translation tables. A directory lookaside table (DLAT) which contains translation lookaside buffer (TLB) entries used for storing previously translated addresses so that they may be reused when the same virtual address is requested. This shortens the time for a processor to obtain most required data.

A TLB entry contains ID's associated with a Segment table origin (STO), a Logical Address (LA), and Translated Real Address. The DLAT is two-way associative via Phi and 1 entries, and multiple compare circuits check whether associative entries compare equal.

A common segment enhancement feature allows multiple virtual system (MVS) programming to specify segments that are common to all address spaces by placing a common flag bit in the entry for each common segment in all segment tables. DLAT entries translated from common segment entries are given a unique ID which compares equal for all address spaces. If programming does not set the common bit in all the common segment entries, a DLAT multiple-compare machine check could result unless action is taken in the DLAT controls to prevent it.

This article describes means to prevent the machine check by recognizing the condition when a compare is done to insure that the DLAT is written correctly when the entry is placed in it. These circuits are shown in the figure. They prevent machine...