Title: Computer footprint file

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1. Apparatus for keeping track of the progress of a computer program by selecting specific operand and/or instruction references, comprising:

means for accessing an operand reference;

means for accessing an instruction reference;

means connected to a memory data register of the computer and to the two accessing means for selecting a specific operand or instruction reference which is to be monitored;

a random-acess memory (RAM), having three inputs, including one from a memory address and one comprising the output from the selecting means for writing the last N instruction and/or operand references, or any combination thereof into the RAM;

a circle counter having an input comprising the same output from the selecting means, for cycling the N references;

means connectd to the circle counter and the RAM of replacing the oldest reference in the RAM by a new reference from the circle counter, that is, for updating the RAM; and

means connected to the updating means for reading out a specific instruction and/or operand reference.

2. The apparatus according to claim 1 wherein the means for selecting a specific reference comprises:

an instruction trap control, connected to the memory data register, for trapping an instruction reference;

an operand trap control, also connected to the memory data register, for trapping an operand reference;

means for setting or clearing the trap controls;

a first AND circuit, whose two inputs are connected to the output of the instruction trap control and to an instruction reference from the computer;

a second AND circuit, whose two inputs are connected to the output of the operand trap control and to an operand reference from the computer; and

an OR circuit, whose two inputs are connected to the outputs of the two AND circuits and whose output comprises one of the inputs to the RAM and the input to the circle counter.

3. The apparatus according to claim 1 wherein the updating means comprises:

an adder, having one input connected to the circle counter and another input connected to the output of the readout means, the adder output constituting a footprint memory address; and

a selector circuit, having one input connected to an output of the readout means, and another input connected to the output of the circle counter, the slector providing a means for reading out a selected footprint memory address.

4. The apparatus according to claim 2, werein the updating means comprises:

an adder, having one input connected to the circle counter and another input connected to the output of the readout means, the adder output constituting a footprint memory address; and

a selector circuit, having one input connected to an output of the readout means, and another input connected to the output of the circle counter, the selector providing a means for reading out a selected footprint memory address.

Other info:

Inventors: Unger, Robert A. (El Cajon, CA, US)

Application Number: 543720
Filing Date: 1975-01-24
Publication_date: 1976-01-27
Assignee: The United States of America as represented by the Secretary of the Navy (Washington, DC)
Primary Class(es): 714/45
Other Classes:
US Patent Ref:

3551659	Dec, 1970	Forsythe	444/1.
3588835	Jun, 1971	Enabnit	340/172.
3588837	Jun, 1971	Rash et al.	340/172.
3593297	Jul, 1971	Kadner	340/172.
3644936	Feb, 1972	Holtwick et al.	444/1.
3707725	Dec, 1972	Dellheim	444/1.
3711863	Jan, 1973	Bloom	444/1.
3721961	Mar, 1973	Edstrom et al.	340/172.

Other Refs:
Primary Examiner: Zache, Raulfe B.
Assistant Examiner:
Attorney: Sciascia; Richard S., Johnston; Ervin F., Stan; John