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To achieve smooth flow of time-triggered communication in a FlexRay cluster, a global clock if required for all FlexRay nodes. This represents a tremendous challenge, since manufacturing tolerances and changing environmental conditions can result in rather large frequency deviations. To satisfy the very strict error tolerance requirements, all local clocks are synchronized by a fault-tolerant clock synchronization mechanism.
This fault-tolerant clock synchronization mechanism is based on prior knowledge of the times at which all of the FlexRay messages are sent and received. This knowledge and the use of a special time hierarchy and algorithm lets all of the FlexRay nodes in a FlexRay cluster correct their offset and frequency so that all FlexRay nodes always begin each communication cycle at the same time and frequency during active communication.
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