  As radiation detector arrays in nuclear physics applications become larger
and physically more separated, the time synchronization and trigger
distribution between many channels of detector readout electronics become more
challenging. Clocks and triggers are traditionally distributed through
dedicated cabling, but newer methods such as the IEEE 1588 Precision Time
Protocol and White Rabbit allow clock synchronization through the exchange of
timing messages over Ethernet. Consequently, we report here the use of White
Rabbit in a new detector readout module, the Pixie-Net XL. The White Rabbit
core, data capture from multiple digitizing channels, and subsequent pulse
processing for pulse height and constant fraction timing are implemented in a
Kintex 7 FPGA. The detector data records include White Rabbit time stamps and
are transmitted to storage through the White Rabbit core's gigabit Ethernet
data path or a slower diagnostic/control link using an embedded Zynq processor.
The performance is characterized by time-of-flight style measurements and by
time correlation of high energy background events from cosmic showers in
detectors separated by longer distances. Software for the Zynq processor can
implement "software triggering", for example to limit recording of data to
events where a minimum number of channels from multiple modules detect
radiation at the same time.
