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Converted Return Interrupt Feature

IP.com Disclosure Number: IPCOM000088994D
Original Publication Date: 1977-Sep-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 2 page(s) / 13K

Publishing Venue

IBM

Related People

Clay, EC: AUTHOR [+2]

Abstract

In a computer system it is common to have multiple interrupt levels with a program status word associated with each level. The program status word defines the machine state for the resumption of execution of a program on each respective level. The program status typically includes the instruction address register; hence, the program status is continually modified as execution of the program transpires.

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Converted Return Interrupt Feature

In a computer system it is common to have multiple interrupt levels with a program status word associated with each level. The program status word defines the machine state for the resumption of execution of a program on each respective level. The program status typically includes the instruction address register; hence, the program status is continually modified as execution of the program transpires.

One of the primary uses of an interrupt system is in the servicing of I/O devices. The devices operate asynchronously to the processor, under real-time control of their individual adapters. When a device completes the operation which has been commanded by the processor or when it has progressed to a point in its operation requiring further servicing, an interrupt request is posted by the control logic in the adapter. The interrupt request is honored by taking an interrupt to the respective level. The program status word associated with that level is used in directing the processor to the proper program for servicing the device. After the device has been serviced, preparation is made for terminating the service routine and for returning to the previous interrupt level. This preparation includes reestablishing the program status word to its original value such that a subsequent interrupt request will cause the device servicing program to be properly entered. Execution on the level is then ended by issuing a termination instruction or sequence of instructions.

The time to reestablish the program status word to the original value is saved if two program status words are assigned to each level. The first is called the initial program status word; reference is made to it whenever an interrupt is initially taken to its respective level. The initial program status word need not be modified at any time in the course of ordinary operation of the computer system. The second is called the return program status word. It is used to store the state of the machine when an interrupt is taken from its respective level to another level, and reference is made to the retur...