US 4,733,353 AGranted

Frame synchronization of multiply redundant computers

AssigneeGeneral Electric Company

InventorVijay C. Jaswa

Life of this patent

Estimating the term…

Loading patent…

Abstract

A frame synchronization method and apparatus wherein each computer system of a multiply redundant processing system periodically executes a frame synchronization procedure in which it sequentially assumes a plurality of different operating states during which it pauses in the execution of a task it was performing and readies itself for synchronization, determines which other computer systems are ready for synchronization, synchronizes itself with one or more of the systems, and then determines which of the other systems has also synchronized itself. At a predetermined frame interval, the procedure is repeated and the computer systems resynchronize themselves with one another. The invention is impervious to stuck-at type faults, and may be embodied either totally or partially in software within each computer system, or in a separate hardware device.

Claims20

Dependent claims

A method of synchronizing a plurality of computer systems at predetermined frame intervals, the method being performed in each computer system and comprising the steps of instructing, at each frame interval, said computer system to set a sync flag and to enter a first state in which program execution is halted;

determining which computer of said plurality have set a sync flag and defining a corresponding first set of computer systems with sync flags set;
comparing the first set to a second set of computer systems which during a prior frame interval had set and then reset sync flags, and transitioning to a second state upon a first predetermined condition being satisfied;
transitioning from the second state to a third state after a first predetermined pause and instructing the computer system to reset its sync flag and restart program execution;
determining, in the third state, which computer systems of said plurality have reset sync flags and defining a corresponding third set of computer systems;
comparing the third set with the second set and transitioning to a fourth state upon a second predetermined condition being satisfied;
transitioning to a fifth state after a second predetermined pause;
updating, in the fifth state, the second set to correspond to those computer systems which had set and then reset sync flags during said foregoing transitioning steps;
and repeating all of the foregoing steps at each subsequent frame interval.

5 more elements

Apparatus for synchronizing a plurality of computer systems at predetermined frame intervals which operates by transitioning between states in a given sequence comprising, for each computer system, means for providing and starting a frame interval timer for timing one frame interval;

means for instructing the computer system after said frame interval has timed out to set a sync flag and to enter a first state at which program execution is halted;
means for detecting a first set of computer systems which have set their sync flags;
means for comparing the first set to a second set of computer systems which had set and then reset their sync flags during a prior frame interval;
means responsive to the comparing means for instructing the computer system to transition to a second state upon a first predetermined condition being satisfied;
means for instructing the computer system to transition from the second state to a third state after a first predetermined pause and to reset its sync flag and to restart program execution;
means for detecting a third set of computer systems having sync flags reset;
means for comparing the third set with the second set and for instructing the computer system to enter a fourth state upon said comparing satisfying a second predetermined condition;
means for instructing the computer system to enter a fifth state after a second predetermined pause;
and means operating in the fifth state for redefining the second set of computer systems as those which had set and then reset their sync flags during said transitions between states.

6 more elements

Dependencies are inferred from the claim text.