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Address Chaining Mode in Channel Operations

IP.com Disclosure Number: IPCOM000073716D
Original Publication Date: 1971-Jan-01
Included in the Prior Art Database: 2005-Feb-22
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Lucas, DJ: AUTHOR

Abstract

Channel command words (CCW) are utilized in IBM System/360 to transfer data between an input/output device and main storage. Presently, the structure of this CCW allows only one block of contiguous storage locations to be handled by one CCW. The addition of a new flag bit to the CCW allows the data transferred under control of a single CCW to be scattered among noncontiguous subblocks of main storage. When the flag bit is zero, the input/output channel executes the CCW in accordance with the ordinary operation of System/360 computers. When the flag bit is a one, an "address chaining" mode of operation is activated in the channel. In this mode of operation, the data address field of the CCW is used to refer to a Table of Addresses, rather than being used as a data address as is currently done in System/360.

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Address Chaining Mode in Channel Operations

Channel command words (CCW) are utilized in IBM System/360 to transfer data between an input/output device and main storage. Presently, the structure of this CCW allows only one block of contiguous storage locations to be handled by one CCW. The addition of a new flag bit to the CCW allows the data transferred under control of a single CCW to be scattered among noncontiguous subblocks of main storage. When the flag bit is zero, the input/output channel executes the CCW in accordance with the ordinary operation of System/360 computers. When the flag bit is a one, an "address chaining" mode of operation is activated in the channel. In this mode of operation, the data address field of the CCW is used to refer to a Table of Addresses, rather than being used as a data address as is currently done in System/360. The actual storage address of the data transfer is obtained from the Table of Addresses. Each address entry in the Table defines the beginning address of a subblock of storage locations. The size of each subblock may be determined by the programmer.

When the boundary of the current subblock is reached, the data address field of the CCW is decremented and used to address the Table of Addresses. The next entry in the Table of Addresses is obtained and is used as the beginning address of the next subblock. This is repeated until the CCW count field is decremented to zero, at which time the address chaining mode flag bit...