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Deriving Computer Instruction Timing Formulae

IP.com Disclosure Number: IPCOM000081783D
Original Publication Date: 1974-Aug-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 2 page(s) / 13K

Publishing Venue

IBM

Related People

Diamond, DH: AUTHOR [+4]

Abstract

In many modern electronic data processing machines, the amount of time (or number of cycles) that it will take to execute a given machine instruction can depend upon a large number of parameters. Instruction execution time for a given operand (or set of operands) can be affected by sign, length, address boundary, ratio of ones to zeros, etc. For many instructions, a formula which precisely describes execution time would be extremely difficult to derive and would be too complex to be of any practical value.

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Deriving Computer Instruction Timing Formulae

In many modern electronic data processing machines, the amount of time (or number of cycles) that it will take to execute a given machine instruction can depend upon a large number of parameters. Instruction execution time for a given operand (or set of operands) can be affected by sign, length, address boundary, ratio of ones to zeros, etc. For many instructions, a formula which precisely describes execution time would be extremely difficult to derive and would be too complex to be of any practical value.

At the other extreme, average execution times can be easily derived by measuring the amount of time that it takes to execute an instruction a given number of times on various types of data. However, the actual execution time for any specific set of operand parameters will probably be quite different from the average execution time. Timing formulae which are both accurate and simple enough to be of value can be both derived and verified as follows. 1- Assumptions are made concerning the significance of variable parameters which reflect the designer's

view of machine timing dependencies. Initial

instruction timing formulae are developed using

the key parameters and various (initially unknown)

constants. 2- A small set of test cases is written for each instruction included in the machine instruction

set. Where possible, each test case is written

so as to include the effect of changing no more

than one parameter. 3- An automatic counting device is attached to the machine under test, to measure the instruction

timing of each test case of item 2. A hardware

interface to the counting device allows for the

triggering and...