Browse Prior Art Database

OEMI Channel Implementation Less Susceptible to Chaining Checks

IP.com Disclosure Number: IPCOM000102599D
Original Publication Date: 1990-Dec-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 2 page(s) / 106K

Publishing Venue

IBM

Related People

Casper, D: AUTHOR [+4]

Abstract

Disclosed is an OEMI parallel channel implementation less susceptible to Chaining Checks than prior known implementations. This is accomplished by parallel data transfer hardware design capable of terminating the pre-acceptance of read data as soon as the end of the CCW record is known, and without waiting for all of the read data to be transferred to main storage.

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This is the abbreviated version, containing approximately 52% of the total text.

OEMI Channel Implementation Less Susceptible to Chaining Checks

       Disclosed is an OEMI parallel channel implementation less
susceptible to Chaining Checks than prior known implementations.
This is accomplished by parallel data transfer hardware design
capable of terminating the pre-acceptance of read data as soon as the
end of the CCW record is known, and without waiting for all of the
read data to be transferred to main storage.

      Chaining Check is an architected channel status bit which is
only applicable to read data-chaining operations. During read data
chaining an OEMI channel must indicate Chaining Check if it has
accepted more read data than specified by the current CCW record.  A
"CCW record" is the entire data transfer between initial selection
and ending status presentation, as perceived by the channel program.
A CCW record either may contain only one CCW if data-chaining is not
specified, or may be made up of multiple Chained-Data-Address (CDA)
CCWs if data chaining is specified.  A "CDA CCW" is one either that
contains the chained-data flag or that does not contain the
chained-data flag but continues data chaining.  A CDA CCW only
contains a valid command code if it initiates the CCW record.  If
data chaining is in effect, then the CCW record ends with the CCW
that contains no chained data-flag.

      This article pertains to an OEMI channel consisting of a serial
channel connected via a serial link to a channel extender unit, which
is connected to the parallel OEMI control unit(s).  During read data
chaining, the extender unit is capable of buffering pre-accepted read
data that has not yet been requested by the serial channel.  If the
extender unit pre-accepts more read data bytes than required to
complete the read CCW record, then the extender unit must detect the
architected Chaining Check.  The extender unit passes the Chaining
Check indication to the serial channel for presentation to the
program.

      The serial channel and extender unit communicate by sending
serial frames to each other.  During a read data transfer, the serial
channel sends one or more read data request frames to the extender
unit, each containing a read data request count.  The extender unit
adds these received read data request counts to two counters, the
Read Data Request (RDR) counter and the Data Request (DR) counter.
The RDR counter may only contain a positive value.  A non-zero value
in the RDR counter gives the extende...