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Segment Table Origin Stack

IP.com Disclosure Number: IPCOM000089308D
Original Publication Date: 1977-Oct-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 2 page(s) / 37K

Publishing Venue

IBM

Related People

Gannon, PM: AUTHOR [+2]

Abstract

The purpose of a Segment Table Origin Stack (STOK) is to buffer the virtual address spaces (VAS) most recently used by data processing system to contain Translation Lookaside Buffer (TLB) entries which simultaneously hold translations for several address spaces. The advantage of using the ID in the DLAT is to significantly reduce the number of bits that must be compared to determine if the entry is in the DLAT. This enables faster machine operation.

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Segment Table Origin Stack

The purpose of a Segment Table Origin Stack (STOK) is to buffer the virtual address spaces (VAS) most recently used by data processing system to contain Translation Lookaside Buffer (TLB) entries which simultaneously hold translations for several address spaces. The advantage of using the ID in the DLAT is to significantly reduce the number of bits that must be compared to determine if the entry is in the DLAT. This enables faster machine operation.

This article describes the STOK data path shown in the figure. It consists of a STO array, a pointer, a counter, FIFO and all the support logic. The array includes 29 entries which respectively represent a different ID to the DLAT. IDs 0 and 1 have other uses, as indicated in the following table: ID USE 0 Invalid 1 Not DAT mode 2-30 STO ID.

The pointer register represents the ID of the STO currently being accessed in the STOK array. FIFO is a register which indicates the ID of the next unused entry in the STOK.

The counter register (CR) contains the pointer ID plus 1. Whenever the machine switches STOs in CR1, the STOK is searched to determine if the new STO in CR1 is in the STOK. The search uses: (1) The pointer register is reset to ID2 as an initial index. (2) The STO is read out of the pointer indexed entry and compared against corresponding bit positions in CRs 0 and 1. If equal, the current pointer value is the active ID, and the operation is terminated. If not equal, the pointer regist...