Undulator gets stuck during energy scan

[prjemian]

As reported by @gfabbris at APS 4-ID-Polar:

This issue seems to be solved with _put_complete = True. I've run dozens of scans after changing it and didn't get stuck. ... It may be good to add it to the apstools.ApsUndulator as I think all beamlines would need it.

Thanks @gfabbris for the suggestion!

[prjemian]

Here's how ophyd.EpicsSignal handles put_complete=True:

        # using put completion:
        # timeout and settle time is handled by the status object.
        st = Status(self, timeout=timeout, settle_time=settle_time)

        def put_callback(**kwargs):
            st._finished(success=True)

        self.put(value, use_complete=True, callback=put_callback)
        return st

[prjemian]

With this change, the original behavior can be obtained in a custom subclass:

class MyUndulator(apstools.devices.ApsUndulator):

    start_button = Component(EpicsSignal, "Start", put_complete=False)