Browse Prior Art Database

Method and Apparatus to Modify CPU Operating Mode via Test Access Port

IP.com Disclosure Number: IPCOM000123931D
Original Publication Date: 1999-Jul-01
Included in the Prior Art Database: 2005-Apr-05
Document File: 1 page(s) / 30K

Publishing Venue

IBM

Related People

Dixon, R: AUTHOR [+3]

Abstract

This invention allows CPU internal operating modes to be modified as a field or manufacturing upgrade . This is an feature for a computer system which does not have the ability to change the CPU internal modes. By utilizing the JTAG connector a microcontroller is able to modify the existing scan chain at initial power on.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 94% of the total text.

Method and Apparatus to Modify CPU Operating Mode via Test Access Port

   This invention allows CPU internal operating modes to be
modified as a field or manufacturing upgrade .  This is an feature
for a computer system which does not  have the ability to change the
CPU internal modes.  By utilizing the JTAG connector a
microcontroller is able to modify the existing scan chain at initial
power on.

   This invention  allows post development modification to
the CPU, without the cost of dedicated function being integrated
into each system.  In addition,  this solution is a minimum cost
solution when the alternative would be to replace the CPU, in order
to change the internal operating mode.  (Internal operating mode here
refers to scan settings that are not accessible by software or by
input configuration pins during initialization.) Changing these
settings is sometimes necessary to correct problems discovered after
a new product release.

   On power up and any subsequent CPU hard reset, the
micro-controller makes corrective action to the CPU internal state
prior to releasing the CPU out of the JTAG test state.

   Below is a sample code fragment used to alter certain scan
bit setting.
      treset 0
    hreset 0
    treset 1
    cop 604 hlt
    "wait 604 -v"
    cop 604 ffrz
    hreset 1
    dirty 604
    "alter 604 yj_sfto_jsrg b'11111100111111111111111111111111'"
    "alter 604 yj_sfto_jsrh b'1111111111111111'"
    flush 604
 ...