Browse Prior Art Database

Interrupting Data Transfers

IP.com Disclosure Number: IPCOM000043111D
Original Publication Date: 1984-Jul-01
Included in the Prior Art Database: 2005-Feb-04
Document File: 3 page(s) / 51K

Publishing Venue

IBM

Related People

Fry, SM: AUTHOR [+3]

Abstract

Transferring data between a host processor and peripheral equipment often employs streaming continuous transmission of a plurality of records, or data sets. Such streaming tends to dominate utilization of a shared resource, such as a data path to peripheral data storage devices of the direct-access storage type, magnetic, optical, etc., and tape recorders. To manage a peripheral subsystem such that all users have an access priority to a shared resource, each received request for access is queued. The access queue is scanned for determining contention with a current streaming operation. For a given contention, access for the queued request is scheduled and the current streaming access is limited to a predetermined number of records yet to be transferred.

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Interrupting Data Transfers

Transferring data between a host processor and peripheral equipment often employs streaming continuous transmission of a plurality of records, or data sets. Such streaming tends to dominate utilization of a shared resource, such as a data path to peripheral data storage devices of the direct-access storage type, magnetic, optical, etc., and tape recorders. To manage a peripheral subsystem such that all users have an access priority to a shared resource, each received request for access is queued. The access queue is scanned for determining contention with a current streaming operation. For a given contention, access for the queued request is scheduled and the current streaming access is limited to a predetermined number of records yet to be transferred. When the additional records have been transferred, the current access is terminated and the scheduled access is established. In direct-access storage devices and tape recorders, the number of records to be continued can be related to the physical access time to the scheduled access. For example, the shared resource may be data flow circuits in a control unit which services a plurality of peripheral data storage devices. Elapsed time for a head seek in a direct-access storage device, or tape motion in a tape recorder, can be predicted and calculated. Then the number of records that would fit within such an elapsed time is calculated and used for limiting the current streaming access such that the data transfer continues in parallel with the peripheral data storage devices establishing the appropriate point of access for the scheduled access request. A plurality of resource users have access to shared resources under control of an access control. The shared resources are data flow circuits in one or more peripheral storage controllers. The peripheral storage controllers are, in turn, connected to a plurality of data storage devices which are also shared, but are not critical insofar as access is concerned. Typically, a resource user will stream data to or from a data storage device through one of the shared data flow circuits. The peripheral system will receive a user command from the same or another user. Initially, the peripheral subsystem determines whether the received command needs a resource. If not, the command is executed. If a resource is needed, then the access request associated with the received user command is qu...