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Efficient Channel Utilization in a Non-Sync Control Unit

IP.com Disclosure Number: IPCOM000106498D
Original Publication Date: 1993-Nov-01
Included in the Prior Art Database: 2005-Mar-21
Document File: 4 page(s) / 159K

Publishing Venue

IBM

Related People

Beardsley, BC: AUTHOR [+5]

Abstract

The Read/Write environment of the 3990 DASD Controller is the set of microcode components which control the transfer of data between the channel and the DASD. For the 3990 DASD Controller and its predecessors, the microcode design has required that the Read/Write environment operate in a synchronous manner. The data transferred between the channel and the DASD is done one record at a time. For example, if writing several data records from the channel to the DASD, the transfer of the second data record from the channel to the controller can not be started until the transfer of the first record from the controller to the DASD has been completed. Two DASD controller microcode components control the transfer of data from the channel to the DASD.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 36% of the total text.

Efficient Channel Utilization in a Non-Sync Control Unit

      The Read/Write environment of the 3990 DASD Controller is the
set of microcode components which control the transfer of data
between the channel and the DASD.  For the 3990 DASD Controller and
its predecessors, the microcode design has required that the
Read/Write environment operate in a synchronous manner.  The data
transferred between the channel and the DASD is done one record at a
time.  For example, if writing several data records from the channel
to the DASD, the transfer of the second data record from the channel
to the controller can not be started until the transfer of the first
record from the controller to the DASD has been completed.  Two DASD
controller microcode components control the transfer of data from the
channel to the DASD.  The Channel Interface Processor (CHIP) controls
the transfer of data from the channel to the DASD controller.  The
Device Interface processor (DIP) controls the transfer of data from
the DASD controller to the DASD.  The DASD controller contains a
storage area (ADT) to buffer the data being transferred between the
channel and the DASD.

      In the synchronous mode of operation, the channel and DASD are
both required to be in the 'ready' state to start the transfer of the
data record.  As a result, both CHIP and DIP will complete their
portions of the transfer at approximately the same time.  Therefore,
the control unit remains connected to the channel for the entire time
it takes for CHIP to transfer the data between the channel and the
ADT buffer and for DIP to transfer the data between the ADT buffer
and the DASD.

      With the introduction of the new ESCON architecture and serial
channels, the Read/Write environment in the 3990 DASD controller has
a new requirement to operate in a non-synchronous fashion.  Using the
previous example where several data records are written from the
channel to the DASD, the transfer of the second data record from the
channel to the controller can be started before the transfer of the
first record from the controller to the DASD has been completed.
CHIP and DIP can now be records apart in the data transfer.  Because
of this property of non-synchronous data transfers, one process,
either CHIP or DIP, can finish well ahead of the other process and be
required to wait an extended period of time for the other process to
finish.

      When the leading R/W process (CHIP on a write and DIP on a
read) has finished every data transfer in the CCW chain or has
completely filled the ADT buffer, it must then wait for the trailing
R/W process.  In a synchronous environment, the channel remains
connected to the control unit through many short wait intervals.  It
is not worthwhile to disconnect from the channel during these short
waits since the time required for channel disconnection and channel
reconnection is longer than the wait interval.  In addition, if the
channel is unavailable...