Browse Prior Art Database

Dynamically Alterable Control Word for Fast Response

IP.com Disclosure Number: IPCOM000080212D
Original Publication Date: 1973-Nov-01
Included in the Prior Art Database: 2005-Feb-27
Document File: 2 page(s) / 52K

Publishing Venue

IBM

Related People

Schaughency, MF: AUTHOR

Abstract

In order to operate higher speed I/O equipment on the Selector Channel of some processors, it is necessary to shorten the response time from Service In to Service 0ut, and shorten the total data service trap.

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Dynamically Alterable Control Word for Fast Response

In order to operate higher speed I/O equipment on the Selector Channel of some processors, it is necessary to shorten the response time from Service In to Service 0ut, and shorten the total data service trap.

One existing Selector Channel data service trap operates as follows: First, there is a link word, necessary in any trap to store the return address and set the priority level. Then there are two conditional branch words, to test whether the operation being performed is a read or a write, and if a read, whether it is forward or backward and skip or not, and whether the count previously went to zero. The next word executed depended on the outcome of the conditional branches, and might increment or decrement the address, store data, fetch data, or neither, and set Service Out or Command Out.

A new technique is shown herein to speed up response time and shorten the data service trap by 1.8 microseconds. The two conditional branch words are eliminated. During Start I/O initialization, the proper control word for the type of operation is placed immediately after the link word. When the count goes to zero, the microcode replaces that word with an unconditional branch to an ending routine. Since with fast devices another Service In may come before that replacement is completed, conditional branch tests for Service In are part of the microcode doing the replacement, yielding a response time as good as the worst cas...