Browse Prior Art Database

Program Transparent Addressing of Direct or Indirect I/O Paths

IP.com Disclosure Number: IPCOM000078010D
Original Publication Date: 1972-Oct-01
Included in the Prior Art Database: 2005-Feb-25
Document File: 2 page(s) / 63K

Publishing Venue

IBM

Related People

Edel, TR: AUTHOR

Abstract

An SCP (System control program) service, logically configures I/O paths between a host CPU (Central processing unit) and I/O devices either directly attached to the CPU, or indirectly attached via a peripheral CPU. The peripheral CPU serves as a communication link between the host CPU and the I/O device. Only one interface to application programs (residing in the host CPU) is needed to address I/O paths of differing physical connection between the host CPU and I/O devices. The application program can address I/O paths either directly or indirectly. Direct addressing is used to address I/O devices (or CPUs) physically connected to the host CPU. An intermediate CPU is not present between the host CPU and the addressed I/O device.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 71% of the total text.

Page 1 of 2

Program Transparent Addressing of Direct or Indirect I/O Paths

An SCP (System control program) service, logically configures I/O paths between a host CPU (Central processing unit) and I/O devices either directly attached to the CPU, or indirectly attached via a peripheral CPU. The peripheral CPU serves as a communication link between the host CPU and the I/O device. Only one interface to application programs (residing in the host CPU) is needed to address I/O paths of differing physical connection between the host CPU and I/O devices. The application program can address I/O paths either directly or indirectly. Direct addressing is used to address I/O devices (or CPUs) physically connected to the host CPU. An intermediate CPU is not present between the host CPU and the addressed I/O device. Indirect addressing is used when the host CPU communicates with a peripheral CPU directing that CPU to address an I/O device, thus reducing I/O interference to the host CPU.

The flow chart (Fig. 2) shows the major functions performed to establish a physical/logical I/O interconnection. When a problem program (executing in the host CPU) issues a request, the SCP stores control information to direct subsequent I/O transfers over a direct or indirect I/O path. When an indirect I/O path is selected, the peripheral CPU must contain an interface routine to communicate with the host CPU. When processing ends, and the problem program resumes processing, any I/O transfer requests for th...