The national spherical torus experiment (NSTX)
currently uses a collection of analog signal processing solutions
for coil protection. Part of the NSTX upgrade (NSTX-U) entails
replacing these analog systems with a software solution running
on a conventional computing platform. The new digital coil
protection system (DCPS) will replace the old systems entirely,
while also providing an extensible framework that allows adding
new functionality as desired. The development of the DCPS was a
multidiscipline engineering effort. The fact that long-trusted yet
presently inadequate protection mechanisms were being replaced
with a first-of-a-kind system at NSTX-U has led to a carefully
crafted, full-featured software design. Real-time concurrent
RedHawk Linux provides the deterministic environment in which
the software runs, and the software architecture follows a unified
modeling language design with industry standard patterns.