Introduction to the General Machine Timing System

The FAIR facility involves a long chain of accelerators which need to be tightly synchronized. An important consideration in the design of the FAIR facility is a high degree of truly parallel operation within the accelerator complex to facilitate the different research programs.

The prime task of the timing system is to trigger and synchronize equipment actions, timed according to the accelerator cycles, and to synchronize devices which have to operate simultaneously. The so-called General Machine Timing system (GMT) must handle 20 ms cycles (present UNILAC) as well as machine cycles and manipulation phases in the order of several seconds for the synchrotrons and up to several hours for the storage rings. The GMT is implemented as an alarm based system: Within a White Rabbit network , all participants share a common notion of time via the White Rabbit PTP protocol. A central Data Master, that broadcasts so-called timing-messages a couple of hundreds ┬Ás ahead of execution time. The messages are distributed via the network to Timing Receivers , where appropriate actions are then executed on-time. Thanks to White Rabbit, synchronous event generation at the timing receivers is guaranteed with the precision provided by White Rabbit (1ns).

White Rabbit is based on a combination of Synchronous Ethernet (SyncE) and the Precision Time Protocol (PTP) as defined in IEEE 1588. Gigabit Ethernet transmission technology is used for fibre transmission lines. Clock propagation to a common grandmaster clock is achieved by using several layers of dedicated White Rabbit switches. The 10 MHz reference clock to the grandmaster is generated by a GPS disciplined oscillator.

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-- DietrichBeck - 7 Nov 2018

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Topic revision: 12 Nov 2018, DietrichBeck
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