Browse Prior Art Database

Method for Terminating I/O Device Data Transfer After Receipt of an Initial Selection Sequence From an I/O Channel

IP.com Disclosure Number: IPCOM000051079D
Original Publication Date: 1982-Aug-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 2 page(s) / 37K

Publishing Venue

IBM

Related People

Oppenheim, RP: AUTHOR [+2]

Abstract

A computer I/O channel can under certain circumstances be cleared of its I/O device control Information without any notification given to the I/O device. The I/O device continues to attempt data transfer but the channel starts a new operation or tests the device for status by issuing an Initial Selection Sequence. A data transfer after this sequence may cause a Channel Error Condition. This article describes a technique for avoiding this error condition which involves detecting the initial selection during a data transfer and then terminating this transfer in an orderly manner.

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Method for Terminating I/O Device Data Transfer After Receipt of an Initial Selection Sequence From an I/O Channel

A computer I/O channel can under certain circumstances be cleared of its I/O device control Information without any notification given to the I/O device. The I/O device continues to attempt data transfer but the channel starts a new operation or tests the device for status by issuing an Initial Selection Sequence. A data transfer after this sequence may cause a Channel Error Condition. This article describes a technique for avoiding this error condition which involves detecting the initial selection during a data transfer and then terminating this transfer in an orderly manner.

As seen in the data flow chart above, the printer channel adapter has an automatic means of setting the interface disconnect status of Channel End and Unit Check when an initial selection sequence is decoded during data transfer mode. The generation of Channel End automatically terminates data transfer mode, and Unit Check indicates that an error condition occurred. No further data transfer is attempted. The control unit does not disconnect from the interface but completes the sequence normally unless an actual interface disconnect is also signaled by the I/O channel.

Interface disconnect status will also be signaled to the controller for the I/O device in order to generate appropriate sense information pointing to the proper error recovery procedure after the channel's accept...