| 摘要 |
Described herein is a distributed computer system having a plurality of computer nodes arranged logically adjacent to each other in a communications ring. Each computer node receives communications from a preceding computer node and sends communications to a succeeding computer node. The computer nodes maintain individual local clocks with local time values c. The clocks are synchronized to each other through a sequence of distributed processing steps. The steps include a step of measuring an approximate local offset d of the local time value of each computer node relative to the local time value of a logically adjacent computer node in the communications ring. A subsequent step includes passing a plurality of collation variables from a lead computer node, through the computer nodes forming the communications ring, and back to the lead computer node in a single pass. The collation variables are processed at each computer node as they are passed around the communications ring. This processing is based at least in part on the measured approximate local offsets d at each computer node. The lead computer then calculates a difference m between its local time value and the mean of the local time values of all the computer nodes based upon the collation variables received back at the lead computer node after being passed around the communications ring. Based upon difference m, values are provided to the distributed computer nodes representing their offsets from the mean. Each computer node then adjusts the rate of its local clock to achieve synchronization. To prevent frequency runaway, each computer node updates its clock through a PLL which limits the amount of correction which can be applied to the local clock.
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