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Hardware Aided Simulator Program

IP.com Disclosure Number: IPCOM000095899D
Original Publication Date: 1964-Sep-01
Included in the Prior Art Database: 2005-Mar-07
Document File: 4 page(s) / 53K

Publishing Venue

IBM

Related People

Tucker, SG: AUTHOR [+2]

Abstract

The addition of certain special hardware and certain special instructions greatly enhances the ability of a computer system to simulate, or execute, a series of programmed instructions originally generated for a different computer system. Two related problems require solution to permit a computer to simulate the programs of another computer. The first relates to how the image of various machine states of the simulated computer are to be held in the simulating computer. The second problem relates to the selection of a small group of special instructions to be added to the language of the simulating machine.

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Hardware Aided Simulator Program

The addition of certain special hardware and certain special instructions greatly enhances the ability of a computer system to simulate, or execute, a series of programmed instructions originally generated for a different computer system. Two related problems require solution to permit a computer to simulate the programs of another computer. The first relates to how the image of various machine states of the simulated computer are to be held in the simulating computer. The second problem relates to the selection of a small group of special instructions to be added to the language of the simulating machine.

A basic problem in computer simulation is the interpretation of the simulated instruction to initiate an instruction routine of the simulating machine for executing the instruction of the simulated program. This can be done by manipulating data within the simulating machine through the use of a plurality instructions in the simulating machine. The number of instructions required for interpretation becomes so great that the desirability of simulating a machine is lessened. If the instruction interpretation can be accomplished in response to a single instruction of the simulating machine, the time required for interpretation can be greatly reduced. Two special instructions, aided by a small amount of hardware, can perform the interpretation fast enough to make simulation desirable.

Two of these special instructions are called DO Interpretative Loop (DIL) and Branch IF.

The DIL instruction replaces, with a single instruction, the plurality of instructions that a simulator would use to access and up-date the simulated instruction counter, convert the address format of the simulated machine to the address format of the simulating machine, fetch the next instruction of the simulated program, perform any indexing required for the simulated instruction, convert the address portion of the simulated instruction to an address format of the simulating machine for obtaining an operand, and interpret the simulated instruction operation code to cause a branch to the appropriate instruction routine of the simulating machine to execute the instruction.

The drawing shows a basic computer system capable of manipulating data in response to either a DIL or Branch IF instruction. The portions which represent a standard computer arrangement include storage 1 containing a series of instructions and operands accessible through address register 2. The system also includes a plurality of general purpose registers 3 which are addressable and contain at least registers for containing a simulated instruction counter 3a, the address portion of a simulated instruction in the address format of the simulated machine 3b, and the address portion of the simulated instruction which has been converted to the simulating machine address format 3c.

Also included, are instruction counter 4, instruction register 5, operation decoder 6, ari...