Browse Prior Art Database

Pad Character Generation and Deletion Mechanism

IP.com Disclosure Number: IPCOM000051462D
Original Publication Date: 1981-Jan-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 3 page(s) / 41K

Publishing Venue

IBM

Related People

Bergey, AL: AUTHOR [+3]

Abstract

Means are provided for appending data to, or deleting data from, fields that pass through an automatic data transfer (ADT) path of a control unit for a direct-access storage device (DASD). The ADT is used for high speed transfer between the system channel and the DASD, where the system channel may be slower than the device. Data flow can be in either direction, channel to device or device to channel, and is necessary to carry out the various DASD read, write and search operations.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 53% of the total text.

Page 1 of 3

Pad Character Generation and Deletion Mechanism

Means are provided for appending data to, or deleting data from, fields that pass through an automatic data transfer (ADT) path of a control unit for a direct- access storage device (DASD). The ADT is used for high speed transfer between the system channel and the DASD, where the system channel may be slower than the device. Data flow can be in either direction, channel to device or device to channel, and is necessary to carry out the various DASD read, write and search operations.

The principal components utilized for data transfer are illustrated in the figure. A first in/first out (FIFO) buffer, operates in a circular mode, through which all data from or to the device flows. All data received from the channel is placed in the buffer. All data sent to the channel comes through the buffer from the device, but not all data from the device is necessarily sent to the channel. The buffer has one bidirectional port associated with the channel, and one bidirectional port associated with the device. There is, additionally, a mechanism to insert or delete pad characters on the device port, in order to fill out recorded blocks on the device when insufficient characters are supplied by the channel on write operations, and to strip off these surplus characters when these same blocks are read later by the channel.

A channel buffer pointer (CBP) addresses the location in the FIFO buffer where data from the channel is stored, and from where going to the channel is fetched. The initial value is supplied by the microprocessor unit (MPU).

A device buffer pointer (DBP) addresses the location in the FIFO buffer where data from the device is stored, and from where data going to the device is fetched. The initial value is supplied by the MPU.

A channel transfer control generates requests for buffer cycles as required by the channel interface transaction. A length counter, loaded by the MPU, controls the number of characters in the transfer with the channel.

A device transfer control generates requests for buffer cycles as required by the device interface transaction. A length counter, loaded by the MPU, controls the number of characters in the transfer with the channel.

A buffer control assigns buffer cycles based on channel or device requests and the relative positions of CBP and DBP.

A comparator provides constant evaluation of CBP and DBP relative to one another, to avoid buffer overflow or underflow.

A record length counter (RLC) is used to provide control of pad character generation when writing, and pad character dropping when reading or searching. The initial value in the record length counter is the initial value in the device counter minus the number of bytes to be padded or dropped.

Previous mechanisms for the generation and deletion of pad characters that depend upon the buffer being empty at the end of the transfer, and the buffer-

1

Page 2 of 3

device and buffer-channel...