Browse Prior Art Database

Phase-Modulated Interrupt Mechanism

IP.com Disclosure Number: IPCOM000112249D
Original Publication Date: 1994-Apr-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 4 page(s) / 100K

Publishing Venue

IBM

Related People

Bergey, AL: AUTHOR [+3]

Abstract

This invention is a mechanism for detecting failures in interrupt signals or other signals that do not change often and are difficult to check. A square-wave clock is exclusive-ORed with the signal to "modulate" it. Failures in which the signal is stuck active or stuck inactive appear as a lack of modulation by the function receiving the signal.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Phase-Modulated Interrupt Mechanism

      This invention is a mechanism for detecting failures in
interrupt signals or other signals that do not change often and are
difficult to check.  A square-wave clock is exclusive-ORed with the
signal to "modulate" it.  Failures in which the signal is stuck
active or stuck inactive appear as a lack of modulation by the
function receiving the signal.

      One of the problems with interrupt signals in a microprocessor
system is that it is difficult to tell if they are broken.
Interrupts are normally off, but turn on to indicate that some
external event has occurred.  If the interrupt signal fails by
turning on, the microprocessor will notice the failure immediately.
But if the signal fails by turning off, the microprocessor may have
great difficulty identifying the problem.

      If an interrupt signal fails off when no interrupt is present,
the system will continue to function normally.  Later, when a real
interrupt occurs, the microprocessor will initially be unaware of
both the interrupt and the failure.  It may eventually discover that
a problem exists, but be unable to identify the hardware failure that
caused the problem.  It may never discover the problem at all and
simply let the external event wait forever.  This kind of failure can
be very difficult to identify.

      Solution - This invention is a mechanism for detecting failures
in interrupt signals or other signals that do not change often and
are difficult to check.

      The mechanism uses a common signal that rises and falls in a
square wave -- up for one cycle, down for the following cycle.  The
square wave is exclusive-ored with the signal where it is generated,
and again where it is received.  Fig. 1 shows the hardware involved,
and Fig. 2 shows a good machine timing chart of the signals.  Since
the signal is exclusive-ored with the square wave twice, the two
cancel out in a good machine, resulting in the same interrupt signal
that would have been received if this mechanism was not used.

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