  The Spallation Neutron Source (SNS) timing and Real Time Data Link (RTDL)
systems are being designed and developed at Brookhaven National Laboratory
(BNL), Los Alamos National Laboratory (LANL) and other SNS collaborating labs
[1]. The VME-based SNS timing system is comprised of a phase locked loop (PLL)
to generate a 120 Hz power line locked clock, a master timing system including
up to 4 16-event input modules (V101) and a timing system encoder module
(V123S), distribution system to all equipment locations, and a timing system
receiver module (V124S). The VME-based SNS RTDL system includes an encoder
module (V105), up to 10 8-inputs modules (V206) and an RTDL receiver module.
The EPICS [2] software support for the timing and RTDL master VME boards has
been developed at BNL while the software and hardware of the SNS utility module
are undertaken at LANL. The software is currently under the beta test at the
SNS collaborating labs. This paper describes the design and the implementation
of the software.
