Synchronizing chained distributed digital chronometers by the use of an

Abstract

A method and apparatus for synchronizing digital chronometers is provided in a distributed digital system having a number of nodes and a global clock for generating clock pulses. A subset of those nodes is coupled to a corresponding synchronizer while other nodes with chronometers are coupled to other synchronizers. Each synchronizer is coupled to at least one other synchronizer and receives clock pulses from the global clock and includes a counter holding a count. A sync signal is propagated in a forward direction from a first synchronizer to a last synchronizer through a chain of synchronizers. The sync signal is received and thereafter the synchronizer count is incremented at each received clock pulse. At the last synchronizer, the asserted sync signal is propagated back as an echo signal in a reverse direction from the last synchronizer to the first synchronizer through the chain of synchronizers. After receipt of the echo signal at a synchronizer, the synchronizer count is halted. Eventually the echo signal is received at the first synchronizer. After receipt of the echo signal at the first synchronizer, a decrement signal is propagated in the forward direction. At each synchronizer after first receipt of the decrement signal, a divided count is decrement upon receipt of each subsequent clock pulse. The divided count is one-half of the count immediately after the count was halted after receipt of the echo signal. When the divided count is decremented to zero, the chronometer associated with the synchronizer is started.