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Microcode Data Event Logging in a Global Variable Environment

IP.com Disclosure Number: IPCOM000110504D
Original Publication Date: 1992-Dec-01
Included in the Prior Art Database: 2005-Mar-25
Document File: 2 page(s) / 94K

Publishing Venue

IBM

Related People

Basham, RB: AUTHOR [+4]

Abstract

This article deals with a programmable microcode mechanism which traces bit manipulation of any specified data area in microprocessor Control Store. This is especially useful in microcode applications where all control data is maintained as global data without any encapsulation. In this environment, unpredictable read/write access to critical data structures can cause severe error conditions which are very intermittent. There is normally little information available for problem analysis from either a built-in microcode dump function or logic analyzer external address trace. This is because of the extensive pathing and the difficulty in distinguishing those microcode instructions which actually alter key data from those which are capable of it.

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Microcode Data Event Logging in a Global Variable Environment

       This article deals with a programmable microcode
mechanism which traces bit manipulation of any specified data area in
microprocessor Control Store.  This is especially useful in microcode
applications where all control data is maintained as global data
without any encapsulation.  In this environment, unpredictable
read/write access to critical data structures can cause severe error
conditions which are very intermittent.  There is normally little
information available for problem analysis from either a built-in
microcode dump function or logic analyzer external address trace.
This is because of the extensive pathing and the difficulty in
distinguishing those microcode instructions which actually alter key
data from those which are capable of it.  Prior to the addition of
function provided by this disclosure, these problems went unresolved
with little hope of resolution.

      This article describes a mechanism developed to dynamically
define and identify any data event of interest, and then log its
occurrence for future analysis.  A data event is defined as a
bit-field state change.

      Data event logging associates a failure scenario very closely
with known accesses to critical data structures.  Ideally, the data
event trace contains known data accesses in a sequence that
identifies the origin of the failure.  In this case, microcode logic
can be quickly corrected.  On the other hand, if the data event trace
shows known accesses in a sequence that does not profile the failure,
then an unknown data access has occurred.  This condition is more
difficult to resolve, however, the context of the unknown data ac...