Browse Prior Art Database

Multiple-Command Decode Tables for Context Switching in a Complex Control Unit Environment

IP.com Disclosure Number: IPCOM000099854D
Original Publication Date: 1990-Feb-01
Included in the Prior Art Database: 2005-Mar-15
Document File: 2 page(s) / 50K

Publishing Venue

IBM

Related People

Benhase, MT: AUTHOR [+6]

Abstract

Decoding Channel Command Words (CCWs) have been accom- plished through the use of one chaining routing and a command decode table. In a complex environment a control unit will take different actions for the same CCW based on the present environment in which the command is received.

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Multiple-Command Decode Tables for Context Switching in a Complex Control Unit Environment

       Decoding Channel Command Words (CCWs) have been accom-
plished through the use of one chaining routing and a command decode
table.  In a complex environment a control unit will take different
actions for the same CCW based on the present environment in which
the command is received.

      Implementation on previous control units had a single chaining
routine which used a single command decode table. The chaining
routine and most of the command processors consumed time verifying
the present environment and context switching if that environment was
not as required.

      An innovative method is to use a separate check chaining
routine and decode table for each environment. Now, context switching
is done strictly via the decode tables, and numerous checks for the
type of environment are not required in the chaining routines and the
CCW processors.  This allows the command processors to assume they
are in the proper environment  and will reduce the number of
instructions executed in time critical code.  The figure shows how
this design would apply to a cached DASD control unit.