Simultaneous resynchronization by command for state machines in redundant systems

Abstract

A redundant system ( ) comprises a first unit ( ), a second unit ( ), and a synchronization server ( ). The first unit ( ) and a second unit ( ) each include plural state machines (SMs) for performing tasks. At least some of the state machines provided at the first unit simultaneously perform same tasks as at least corresponding ones of some of the state machines provided at the second unit. When a state machine of the second unit needs to be resynchronized, the synchronization server ( ) receives a resynchronization request ( ) from the resync requesting state machine of the second unit and thereupon provides an out-of-synchronization indication ( ) to a corresponding state machine of the first unit. In response to the out-of-synchronization indication ( ) from the synchronization server, the corresponding state machine of the first unit generates a resynchronization request ( ) at an time deemed appropriate by the corresponding state machine. In response to the resynchronization request ( ) from the corresponding state machine, the synchronization server issues a resynchronization command ( ) to both the resync requesting state machine of the second unit and the corresponding state machine of the first unit, thereby causing simultaneous resynchronization. At least one of the first unit and the second unit includes restart logic that prescribes an order of restart of the plural state machines, thereby providing a gradual start up of the state machines of the redundant units. Thereafter each of the plural state machines controls its own resynchronization.