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Browse Prior Art Database

Device Participation in Data Chaining

IP.com Disclosure Number: IPCOM000119812D
Original Publication Date: 1991-Mar-01
Included in the Prior Art Database: 2005-Apr-02
Document File: 2 page(s) / 70K

Publishing Venue

IBM

Related People

Elliott, JC: AUTHOR [+3]

Abstract

Disclosed is a means by which the I/O device is informed of when transitions between channel command words (CCWs) is occurring within the channel because of data chaining and certain information contained in the new channel command word is passed to the I/O device.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Device Participation in Data Chaining

      Disclosed is a means by which the I/O device is informed
of when transitions between channel command words (CCWs) is occurring
within the channel because of data chaining and certain information
contained in the new channel command word is passed to the I/O
device.

      When there are successive CCWs to be executed by the channel
for a single I/O operation, the execution of these successive CCWs is
referred to as data chaining.  As each CCW associated with a channel
program becomes the current CCW being executed by the channel, the
channel transfers a chain-data bit, count and other flags associated
with this CCW to the control unit.  In this manner, the control unit
is informed that data chaining is specified for the current CCW.
When the execution of the current CCW is completed and the chain-data
bit for this CCW is set to one, data chaining takes place, provided
no abnormal conditions are detected. When data chaining takes place
at the channel, the flags and count held at the control unit are
updated for the current command and the chaining bit CH and
data-chaining-update bit DU are both used to identify data chaining.

      When the control unit receives both the DU bit and CH bit, the
control unit has the data-chaining condition set, and with the chain-
data bit for the previous CCW being on, the count and other flags are
accepted and become the current count and flags.

      The chain-data bit indicates that the control unit will be
updated with the count and flags from a subsequent CCW for the
current operation when that CCW becomes the current CCW.

      The I/O device ensures that data chaining is occurring at the
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