Browse Prior Art Database

Writeable Control Store Protection

IP.com Disclosure Number: IPCOM000039850D
Original Publication Date: 1987-Aug-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 3 page(s) / 39K

Publishing Venue

IBM

Related People

Rogers, MD: AUTHOR [+3]

Abstract

A method is described which provides user protection when accessing a writeable, shareable Control Store without degrading key performance values. A block diagram of a writeable Control Store (CS) is shown in Fig. 1. The basic method of loading the Control Store is at Initial Program Load (IPL) time by system software. Both read CS and write CS instructions are provided. No protection is needed because the user does not have access to CS during IPL after power-on. Added flexibility can result, however, if the CS can be loaded during run-time by the system or by the user. This flexibility supports machine, customer, or application customization of the function of the card.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 54% of the total text.

Page 1 of 3

Writeable Control Store Protection

A method is described which provides user protection when accessing a writeable, shareable Control Store without degrading key performance values. A block diagram of a writeable Control Store (CS) is shown in Fig. 1. The basic method of loading the Control Store is at Initial Program Load (IPL) time by system software. Both read CS and write CS instructions are provided. No protection is needed because the user does not have access to CS during IPL after power-on. Added flexibility can result, however, if the CS can be loaded during run-time by the system or by the user. This flexibility supports machine, customer, or application customization of the function of the card. Along with the flexibility, an exposure arises in that user access suggests the possibility that one user, accidentally or intentionally, could alter the shareable microcode in such a way as to impact all users in a multi-user environment.

Various techniques have been suggested which protect the users, but key performance areas are usually impacted. Protection methods are described which avoid some of the expected performance degradations.

(Image Omitted)

The Control Store can reside in one of two states (NORMAL, CS) as shown in the state diagram of Fig. 2. The CS instructions are defined as follows: RE CS = Read CS

WR CS = Write CS

ENA CS = Enable CS Mode

DIS CS = Disable CS Mode In CS mode, RD CS, WR CS, and DIS CS will execute and all others will be rejected via an EXCEPTION. In NORMAL mode, operation is symmetrical in that RD CS, WR CS, and DIS CS will be rejected via EXCEPTION, but all others (including ENA CS) will be executed. An exception causes control to be passed to an "exception HANDLER," which is part of system software. Protection is provided in...