Browse Prior Art Database

Virtual Control Store for Floating-Point Operating

IP.com Disclosure Number: IPCOM000039432D
Original Publication Date: 1987-Jun-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 3 page(s) / 21K

Publishing Venue

IBM

Related People

Voltin, JA: AUTHOR

Abstract

A method is described which makes it possible to support an unlimited amount of floating-point (FP) function via microcode stored in control store, even though control store is limited in size. Use of control store and a sequencer for storing/executing microcode is a popular design technique used today because of the flexibility/generality afforded by this approach. This is especially true when horizontal microcode is utilized in that all major functional elements under microcode control can be independently utilized, thereby supporting a high degree of parallelism. (Image Omitted) Fig. 1 shows a general hardware structure supporting the microcode concept. Fig. 2 shows how the Control Store (CS) is partitioned to support multiple function.

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Virtual Control Store for Floating-Point Operating

A method is described which makes it possible to support an unlimited amount of floating-point (FP) function via microcode stored in control store, even though control store is limited in size. Use of control store and a sequencer for storing/executing microcode is a popular design technique used today because of the flexibility/generality afforded by this approach. This is especially true when horizontal microcode is utilized in that all major functional elements under microcode control can be independently utilized, thereby supporting a high degree of parallelism.

(Image Omitted)

Fig. 1 shows a general hardware structure supporting the microcode concept. Fig. 2 shows how the Control Store (CS) is partitioned to support multiple function. Each function (opcode) generally has a unique entry point address and a unique length (associated number of microcode words). A microcode word is the contents of a Control Store Address. In many cases, such as for floating point, it is necessary to implement control store out of high-speed RAM (25 - 35 nsec) in relative small sizes (2kx8, 4kx4, etc.). As a result, it is difficult to justify an arbitrarily large CS since it is costly and also consumes a significant amount of card space. However, the number of functions that may be required is relatively unbounded. A technique whereby an unbounded number of functions can be supported with a small control store is described.

If every function supported must always be resident in CS, thereby providing instant access, the total CS capacity would be However, for a large majority of all machines, there are three classes of functions as follows: 1) High Usage (Base) Functions - these are used often by all

users. Examples include ADD, mult, etc. These should always

be resident in CS; they are loaded at IPL time only.

2) Moderate Usage Functions - These are standard numerical

functions, which are seldom used by the average user, but

often used by particular users. Examples include tan(x), 'y',

to 'x' power, etc. These should be loadable eithe...