Application Connections

Ophyd Signals

Typhos takes advantage of the flexible data plugin system contained within PyDM and the abstraction of the “control layer” within Ophyd. In the SignalPanel, objects signals are queried for their type. If these are determined to be coming from EPICS the data plugin configured within PyDM is used directly, any other kind of signal goes through the generic SignalPlugin. This uses the subscription system contained within Ophyd to keep widgets values updated. One caveat is that PyDM requires that channels are specified by a string identifier. In the case of ophyd.Signal objects we want to ensure that these are passed by reference to avoid duplicating objects. This means the workflow for adding these has one more additonal step where the Signal is registered with the PyDM plugin.

from typhos.plugins import register_signal

# Create an Ophyd Signal
my_signal = ophyd.Signal(name='this_signal')
# Register this with the Plugin
register_signal(my_signal)
# This signal is now available for use with PyDM widgets
PyDMWidget(channel='sig://this_signal')

Note that this is all done for you if you use the SignalPanel, but maybe useful if you would like to use the SignalPlugin directly.

Inclusion of Metadata

In many cases just knowing the value of a signal is not enough to accurately display it. Extra pieces of information such as the units and precision of information can provide a richer operator experience. Typhos counts on this information being available in the output of describe method of the signal. If you want your child ophyd.Signal class to convey this information make sure that it is expressed properly in the output of describe.

Metadata	Description Key
Precision	“precision”
Enumeration Strings	“enum_strs”
Engineering Units	“units”

Happi Plugin

The PyDM Plugin interface makes no mandate about the type of signals that we connect to our widgets. The HappiPlugin and corresponding HappiChannel contains alternative signals in order to send entire ophyd objects from a stored database to our widgets. This is useful where we want to populate a template with an entire devices signals instead of connecting widgets one by one.