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Conditional Control Store Latch Freeze

IP.com Disclosure Number: IPCOM000088776D
Original Publication Date: 1977-Aug-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 2 page(s) / 38K

Publishing Venue

IBM

Related People

Leininger, JC: AUTHOR [+2]

Abstract

The number of times a microword is fetched from a control store and executed when a conditional branch function is being executed can be reduced by a control store latch freezing technique, which makes it unnecessary to access the iterative microword repeatedly and enables the next microword to be accessed sooner than it otherwise would be.

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Conditional Control Store Latch Freeze

The number of times a microword is fetched from a control store and executed when a conditional branch function is being executed can be reduced by a control store latch freezing technique, which makes it unnecessary to access the iterative microword repeatedly and enables the next microword to be accessed sooner than it otherwise would be.

In conventional microprocessors, a microword which calls for execution of a conditional branch function must be accessed repeatedly in the control store until the condition is met. Thus, designating the iterative microword as "N" and the branch function it executes as "cycle A", microword N is repeatedly accessed and read into the control store latches for causing successive executions of the iterative loop (cycle A) until there occurs a loop whose end result meets the branch condition. However, the final accessing of microword N, which occurs just before the condition is met, will cause an unnecessary execution of cycle A to occur right after the condition is met, as indicated in Fig. 1. The time spent in accomplishing this last execution of cycle A is wasted and unnecessarily delays the accessing of control word N + 1 and the following execution of cycle B.

In accordance with the present technique illustrated in Fig. 2, the accessing of a microword N, which calls for a conditional branch function, will automatically cause the output latches of the control store to "freeze" for retaining...