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Address Exception Settable Keys

IP.com Disclosure Number: IPCOM000042297D
Original Publication Date: 1984-May-01
Included in the Prior Art Database: 2005-Feb-03
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Saurel, A: AUTHOR [+2]

Abstract

The subject exception mechanism detects attempts to access uninstalled storage in a data processing system. Address exception (AE) keys are set by the control program using a special instruction. The checking of the AE key associated with each storage segment during each storage operation is performed by the exception mechanism. An exception bit is assigned to each N-byte block of storage. This bit is set to 1 for those blocks for which the storage is not installed. It must be initialized for all M blocks of storage whether installed or not.

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Address Exception Settable Keys

The subject exception mechanism detects attempts to access uninstalled storage in a data processing system. Address exception (AE) keys are set by the control program using a special instruction. The checking of the AE key associated with each storage segment during each storage operation is performed by the exception mechanism. An exception bit is assigned to each N- byte block of storage. This bit is set to 1 for those blocks for which the storage is not installed. It must be initialized for all M blocks of storage whether installed or not. The program executes M special instructions setting the content of the storage address register (SAR) with the following format:

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This way of initializing the address exception mechanism allows specifying that any N-byte segment of a storage card is not available although installed on the machine. This can be useful to keep a program patch area, for example, which cannot be used by the customer programmer, the diagnostics or the operating control program. It is therefore guaranteed free for the software debug team. When the exception mechanism has been enabled and a read or write from a memory location is attempted within a N-byte block with the exception bit on, the following actions are taken: - in program mode, a program address exception level 1 interrupt will result, - during an adapter operation, an input/output control address exception level 1 interrupt will occur and a...