Browse Prior Art Database

Enterprise System Architecture/390 Programs

IP.com Disclosure Number: IPCOM000112171D
Original Publication Date: 1994-Apr-01
Included in the Prior Art Database: 2005-Mar-26
Document File: 4 page(s) / 133K

Publishing Venue

IBM

Related People

Hennessey, JP: AUTHOR [+2]

Abstract

This invention pertains to the IBM System/370* and Enterprise Systems Architecture/390* (ESA/390*) computer architectures. A method is described which allows subchannel status to be cleared at I/O interruption time from the view of a System/370 application and to simultaneously allow the subchannel to be status pending from the view of a ESA/390 application. This is accomplished by creating a new subchannel status called vestigial status.

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Enterprise

System Architecture/390 Programs

      This invention pertains to the IBM System/370* and

Enterprise


Systems Architecture/390* (ESA/390*) computer architectures.  A
method is described which allows subchannel status to be cleared at
I/O interruption time from the view of a System/370 application and
to simultaneously allow the subchannel to be status pending from the
view of a ESA/390 application.  This is accomplished by creating a
new subchannel status called vestigial status.

      In an environment where an ESA/390 processor runs an ESA/390
operating system, it is possible that a System/370 application may
need to be executed which makes use of System/370 architected I/O
facilities.  In this case it is possible that an I/O interruption may
be seen by both programs.  For details of the I/O instructions and
interruption handling referenced to below, see [1,2].

      An issue that must be dealt with when sharing I/O interruptions
in this heterogeneous environment is that of a System/370 application
that replaces the ESA/390 operating system's I/O New PSW with its own
System/370 I/O New PSW.  In this case the possibility exists that the
System/370 application will find this interruption "uninteresting"
and pass control on to the ESA/390 I/O interruption handler.
Therefore, both formats are stored since it cannot be known a priori:
if the System/370 program or the ESA/390 program will handle the
interruption.  What further complicates this is that under
System/370, a side effect of an I/O interruption is to clear the
status pending at the subchannel.  The ESA/390 architecture does not
call for this side effect; rather, the subchannel remains
status-pending until the Test Subchannel instruction is executed (or
the status is cleared another way).  So, the basic problem that had
to be solved was how at interruption time to make a subchannel
non-status-pending for the System/370 program and simultaneously
leave it status pending for the ESA/390 program.  To solve this
apparent contradiction a new kind of subchannel status, called
vestigial status, was created.

      When an I/O interruption occurs and a possible System/370 I/O
New PSW exists, two things must be done:

o   Present a hybrid interruption by storing parameters in both
    System/370  and ESA/390 format and locations.

o   Mark the status in the subchannel as vestigial status.

      When a hybrid I/O interruption is presented, the pending
interruption condition is cleared at the subchannel, and subchannel
status is stored in the form of a System/370 Channel-Status Word
(CSW), but this status also remains pending in the subchannel as
vestigial status.  By implementing the following rules for handling
vestigial status, both System/370 and ESA/390 programs will see
behavior compatible with their architectures.

      If TSCH or STSCH is executed against a subchannel which has
vestigial status pending, the instruction is executed as i...