Browse Prior Art Database

Terminal Handling System

IP.com Disclosure Number: IPCOM000076041D
Original Publication Date: 1971-Dec-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 4 page(s) / 19K

Publishing Venue

IBM

Related People

Harrison, WH: AUTHOR

Abstract

A terminal handling system is described, which can handle the conflicting requirements placed on the design of programs for handling telecommunications equipment attached to a computer system. The conflicting requirements are caused by the need for extremely fast response to different terminal requests, which demand different amounts of processing. The variation in applications with which the terminals may communicate ranges from conversational to information accumulation; and different pieces of terminal hardware may have no common characteristics other than their attachment to the system.

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Terminal Handling System

A terminal handling system is described, which can handle the conflicting requirements placed on the design of programs for handling telecommunications equipment attached to a computer system. The conflicting requirements are caused by the need for extremely fast response to different terminal requests, which demand different amounts of processing. The variation in applications with which the terminals may communicate ranges from conversational to information accumulation; and different pieces of terminal hardware may have no common characteristics other than their attachment to the system.

A terminal handler program consists of several logically distinct components: the Interrupt Handler (IH), a set of Terminal Control Tasks (TCT's), a set of Terminal Handling Modules (THM's) and an Answering Service (AS). The Answering Service is one of a generic class of programs called Terminal Oriented Programs (TOP's), but is the only TOP properly considered part of the Terminal Handler since other TOP's are generally tailored to a specific kind of application such as message processing or time sharing.

In addition to these programs, the terminal handler program makes use of several tables called the Address Control Blocks (ACB's) and the THM indices. There is one ACB for each device address to which a terminal may be connected plus one for each terminal on a multidrop line. The ACB contains information relating the terminal to the TOP which is using it and information describing the current state of the line and terminal. The THM indices are used to locate the appropriate THM to process a terminal event. The Interrupt Handler (IH).

The IH performs queuing of I/O and Supervisor Call (SVC) interrupts. There exists one SVC (called THSVC) which is used by all TOPs to request operations on their terminals. The parameters of THSVC are: a relative terminal number used to denote which of the terminals associated with a TOP is to be operated upon, an operation code, and the address of some further parameter information. The meaning of the latter parameters is left to the THM performing the processing for that terminal.

When an I/O interrupt occurs, the IH allocates a queue element and places into it the channel status and sense information. The device address which produced the interrupt is used to locate an ACB, and the queue element is placed on the work queue for that ACB. The element is placed after all I/O interrupt elements but before the first SVC element.

When an SVC interrupt occurs, the 1H allocates a queue element and places the operation code and parameter address into it. It then uses the relative terminal number to locate the appropriate ACB and places this queue element at the end of the work queue for that ACB.

When a queue element is placed on an ACB, the ACB is placed on a system- wide terminal work queue unless it is already queued. If any TCT is waiting for work, it is activated.

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