Browse Prior Art Database

USE OF DDT WITH "INTERRUPTS-ON" PROGRAMS

IP.com Disclosure Number: IPCOM000128424D
Original Publication Date: 1967-Jul-01
Included in the Prior Art Database: 2005-Sep-15
Document File: 3 page(s) / 23K

Publishing Venue

Software Patent Institute

Related People

Brender, Ronald F.: AUTHOR [+3]

Abstract

This memo describes the modification and use of DEC-provided DDT with programs using the "program interrupt" hardware of the PDP-7.

This text was extracted from a PDF file.
This is the abbreviated version, containing approximately 53% of the total text.

Page 1 of 3

THIS DOCUMENT IS AN APPROXIMATE REPRESENTATION OF THE ORIGINAL.

USE OF DDT WITH "INTERRUPTS-ON" PROGRAMS

Ronald F. Brender

THE UNIVERSITY OF MICHIGAN Memorandum

CONCOMP: Research in Conversational Use of Computers
F. H. Westervelt, Director

ORA Project 07449

supported by:

DEPARTMENT OF DEFENSE
ADVANCED RESEARCH PROJECTS AGENCY WASHINGTON, D. C.

CONTRACT NO. DA-49-083 OSA-3050

ARPA ORDER NO. 716

administered through:

OFFICE OF RESEARCH ADMINISTRATION ANN ARBOR July 1967

This memo describes the modification and use of DEC-provided DDT with programs using the "program interrupt" hardware of the PDP-7.

1. Usage

DEC Debugging Tape (DDT) and user programs are loaded in the normal manner. The restart entry remains at 160008 and forces interrupts off. DDT may be used exactly like the original DDT without knowledge of these modifications.

The modifications to DDT are concerned with facilitating control of the program interrupt as control moves between DDT and user programs and back. Two status words control the program interrupt:

SAVIOS contains the input-output status word when DDT is entered via breakpoint. FIXIOK contains a code indicating the desired state of the program interrupt on exit to user program.

FIXIOK is set by the following commands (which remain in effect until the next is given):

STIOF' leaves program interrupt off when exiting to user programs (This is the default condition.)

STION' turns program interrupt on when exiting to user program.

STIOC' turns program interrupt on when exiting to user program if it was on at the last breakpoint entry.

The latter is particularly useful when continuing a program with"!" . Note that a counted continue will have the desired effect #commands are always executed with interrupts off.

University of Michigan Page 1 Jul 01, 1967

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USE OF DDT WITH "INTERRUPTS-ON" PROGRAMS

The value of SAVIOS may be determined by examining register 154548. Interrupts may be easily "lost" since DDT runs with interrupts off and senses these devices' program flags directly.

The feature described in the next three paragraphs is normally suppressed. It may be invoked by storing a 'NOP' in location 155418.

In addition, after turning interrupts off on a breakpoint entry, DDT loops approximately 140 milliseconds to determine if a character is being printed. The teleprinter flag is tested at the end of this loop and the state saved.

When continuing with "!" or "", DDT prints a null character just before transferring to the user program if the teleprinter flag was up on entry. This will result in a teleprinter flag coming up after reaching the user program.

This flag may be prevented by storing a one in location 154558. Conversely, this flag may be forced on with "DZM 15455 #".

2. Modifications

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