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I/O Interrupt Stacking and Passing Back by the Dynamic Support System

IP.com Disclosure Number: IPCOM000078725D
Original Publication Date: 1973-Feb-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 2 page(s) / 13K

Publishing Venue

IBM

Related People

Cambi, CG: AUTHOR [+3]

Abstract

Summary: The Dynamic Support System (DSS) provides software debugging support to VS/370 which does not interfere with, and is unnoticed by, the operating system. In the I/O area, this means that DSS must at certain times receive I/O interrupts belonging to the operating system, and hold them until an appropriate time to pass them back.

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I/O Interrupt Stacking and Passing Back by the Dynamic Support System

Summary:

The Dynamic Support System (DSS) provides software debugging support to VS/370 which does not interfere with, and is unnoticed by, the operating system. In the I/O area, this means that DSS must at certain times receive I/O interrupts belonging to the operating system, and hold them until an appropriate time to pass them back. Description:

The technique employed by DSS to stack and pass back I/O interrupts consists of placing an SVC (Supervisor Call) instruction in various system modules, which causes DSS to take control. These control points are:
1) At the beginning of the I/O FLIH (First Level Interrupt

Handler).
2) After the SIO (Start I/O) instruction in the IOS (I/O

Supervisor) SIO Subroutine.
3) After the TIO (Test I/O) instruction in the IOS DASIO (Direct

Access SIO) Subroutine.
4) Immediately before IOS enables the system in the Channel

Restart Initialization Subroutine.
5) Immediately before the sense SIO instruction in the IOS

Sense Subroutine.
6) On the LPSW (Load Program Status Word) instruction in the

dispatcher which enables the system.
7) On the LPSW instruction in the I/O FLIH.

When DSS is in the system but has not been initialized, no DSS control SVCs have been enabled so no I/O interrupts are received by DSS. When DSS is in the process of initialization, it is running disabled and I/O interrupts meant for the system will only come into DSS if the DSS I/O routine must clear a channel, control unit path to a device. I/O interrupts pending for the system must then be let in and stacked. At the end of DSS initialization when the control SVC's have been placed i...