At the lowest level, it receives and sends
all of the input and output across the PCIe I/O cards that
connect DCPS to the outside world. This includes initializing
and configuring each card and running several threads to
continually move data on and off the various cards. The input
side is a combination of analog signals, digital signals, and
interrupts from the RCIM.
The link that synchronizes reads between all inputs across
two card types and three cards total is the RCIM. The
NSTX-U facility clock strobes the RCIM in synchronization
with the rest of the NSTX-U system. The RCIM has software
hooks to trigger user space code without requiring kernel space
interrupt handling routines, translating into dispatch latencies
in the order of 2 μs in heavily loaded testing scenarios.