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Method of Testing System Memory that Contains the Test Code

IP.com Disclosure Number: IPCOM000122424D
Original Publication Date: 1991-Dec-01
Included in the Prior Art Database: 2005-Apr-04
Document File: 2 page(s) / 55K

Publishing Venue

IBM

Related People

Cox, DA: AUTHOR [+3]

Abstract

This article describes a method for code to test memory without requiring that the test code be placed in the memory to be tested.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 71% of the total text.

Method of Testing System Memory that Contains the Test Code

      This article describes a method for code to test memory
without requiring that the test code be placed in the memory to be
tested.

      In some computer systems, the system memory uses error
correction code (ECC) to add reliability.  The ECC circuit corrects
errors if only one bit is incorrect, and flags errors if more than
one bit is incorrect.  The ECC circuitry is tested by the power-up
initialization code within the system ROM, and also by the diagnostic
program for the system.

      The system diagnostic program provides in depth tests for the
system's components.  Therefore, the program needs to test the memory
circuitry.  The diagnostic program normally resides in system memory
monitored by the ECC circuitry.  This situation makes memory testing
difficult because the diagnostic code being executed alters the ECC
registers.  This same problem may exist for systems using parity
schemes for memory.

      An interface can be provided in the system ROM initialization
program which loads pointers to a memory read routine and a memory
write routine.  The diagnostic program can call the routines
referenced by these pointers to read or write memory without
affecting the contents of ECC registers.  This ensures that pertinent
ECC information is preserved.  The pointers are stored in
battery-backed memory so that system memory is unaffected.  The
actual code is in the system ROM, and...