Browse Prior Art Database

Building an ESA Mode I/O Based on S370 Mode

IP.com Disclosure Number: IPCOM000108683D
Original Publication Date: 1992-Jun-01
Included in the Prior Art Database: 2005-Mar-22
Document File: 2 page(s) / 82K

Publishing Venue

IBM

Related People

Bolan, JE: AUTHOR [+2]

Abstract

This article describes a method to emulate ESA I/O instructions using existing System/370* (S370) I/O support. It describes the design point used on the 9221 processors (Release 2 and forward) which support Integrated I/O Processors (IOPs). This approach utilizes the idea that the channel subsystem engine which resides within the central processor should perform as much ESA function as possible and that the outboard IOP which acts like a channel should implement only that function which cannot be performed inboard by the channel subsystem engine. This approach also expects that the IOP will emulate as much ESA function as possible using existing S370 code.

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Building an ESA Mode I/O Based on S370 Mode

       This article describes a method to emulate ESA I/O
instructions using existing System/370* (S370) I/O support. It
describes the design point used on the 9221 processors (Release 2 and
forward) which support Integrated I/O Processors (IOPs).  This
approach utilizes the idea that the channel subsystem engine which
resides within the central processor should perform as much ESA
function as possible and that the outboard IOP which acts like a
channel should implement only that function which cannot be performed
inboard by the channel subsystem engine.  This approach also expects
that the IOP will emulate as much ESA function as possible using
existing S370 code.

      The IOP S370 code used is based on the 9370 Model 90 IOP code
plus some additional support which is required for EA mode.  The
following additional requirements and restrictions were added to the
S370 9370 base coreload in order to provide the necessary support for
EA and ESA modes:
 .   Channel Data Check (CDC)
 .   31-bit Indirect Data Address Word (IDAW)
 .   Suspend/Resume
 .   Program Check 16-megabyte boundary cross - no wrap to zero
 .   Emulated ESA I/O instructions using existing S370 instruction
 .   IOP reply messages restructured to provide sufficient
information to build ESA architected interrupts
 .   S370 error information translated into ESA equivalent support

      Much of the reduction in IOP effort is accomplished by ESA
instruction emulation through the use of S370 instructions.  The
emulated instructions are translated into S370 Unit Write messages
and sent to the IOPs for channel program execution.  There are three
ESA instructions which are translated into S370 IOP Unit Write
Messages.  Some modifications were made to the Unit Write messages to
allow for additional ESA specific information.  The three ESA
instructions and their emulated S370 instruction ar...