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Wrong Branch Wrong Store Program Error Detection

IP.com Disclosure Number: IPCOM000080370D
Original Publication Date: 1973-Dec-01
Included in the Prior Art Database: 2005-Feb-27
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Wilmot, GR: AUTHOR

Abstract

The objective of this procedure is to improve the reliability of system performance. The specific objective is to guard against the wrong branch type of error or the wrong store type of error which are difficult to diagnose.

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Wrong Branch Wrong Store Program Error Detection

The objective of this procedure is to improve the reliability of system performance. The specific objective is to guard against the wrong branch type of error or the wrong store type of error which are difficult to diagnose.

The procedure makes use of IBM System/370 hardware facilities, which provide two different kinds of keys. One key is for each 2K byte block of storage and is called the storage key. The second is a protection key, which is placed on the current Program Status Word (PSW) in the CPU. In order for a store from the CPU to storage to take place in System/370, the key in the current PSW must be zero or match the key of the block of storage into which the store is to take place. If the two keys do not match, a program interruption will occur.

This procedure provides that the routines of a program reside in storage, with a different storage key assigned to each of the various routines. In this manner, control blocks and work area residing in storage will have the same storage key, only as the routine to which they belong. Finally, each routine executes under a protection key equal to its storage key.

Through those provisions, a wrong store is detected since a storing routine must specify the storage key of the location into which it is attempting to store, and it must set a matching protect key in the current PSW. If there is no match, an interrupt will occur.

The wrong branch problem is also found thr...