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Instruction Nullification by Saving and Restoring Architected Data

IP.com Disclosure Number: IPCOM000052117D
Original Publication Date: 1981-Apr-01
Included in the Prior Art Database: 2005-Feb-11
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Dale, SP: AUTHOR [+4]

Abstract

In large computing systems. it is necessary to nullify instructions under certain conditions. For example, this can occur when the program crosses a memory boundary and the next page is not available in memory.

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Instruction Nullification by Saving and Restoring Architected Data

In large computing systems. it is necessary to nullify instructions under certain conditions. For example, this can occur when the program crosses a memory boundary and the next page is not available in memory.

In some systems, each instruction is checked by microcode to ensure that it would not be necessary to nullify the instruction after it began execution. This involves a substantial amount of time. In other systems, a hardware check was added to the system which checks each instruction. If this hardware check indicated that the instruction could cross a memory boundary, a microcode routine then examines the particular instruction to see how long that instruction is and to determine if, in fact, a boundary would be crossed.

In computing systems which have retry circuitry for machine instructions (as contrasted to retry circuitry for microwords) a performance improvement can be obtained by removing the check sequence from the "normal case" of how instructions are interpreted and only taking action when it is, in fact, found that an instruction cannot be processed to completion due to the lack of certain data.

In this type of system, no checking of any instruction is done before execution of the instruction is started. If after the instruction begins its execution cycle, it is determined that the instruction cannot be completed because it does not have all the data, execution of the instruction...