units & offset updates not correct in Diffractometer

[prjemian]

Example was revised and tested. The tests have exposed some problems with how changes in units and offset are handled by the Diffractometer() class.

Need to revise how Diffractometer() responds to changes in units and offset signals. One problem observed is how the energy signal is affected when offset is changed.

Originally posted by @prjemian in #121 (comment)

[prjemian]

Several things are off:

• example should use energy_units, not energy_EGU`
• should not set hkl.diffract.Diffractometer.energy in the Diffractometer() class
• all PV update callbacks should not set self.calc.energy, instead call self._update_calc_energy()
• ignore the value argument in self._update_calc_energy()

[prjemian]

When testing including a real EPICS IOC, used PVs from a soft IOC in lieu of a real monochromator. Here's the test daatabase record file for EPICS softIoc -d registers.db test command"

# file: registers.db
#
# purpose: test example for issue #72
# connect control system energy with diffractometer

record(ao, "EPICS:energy") {
  field(DESC, "monochromator energy")
  field(PREC, 5)
  field(EGU, "keV")
  field(VAL, 12.0)
}

record(ao, "EPICS:energy:offset") {
  field(DESC, "monochromator energy offset")
  field(PREC, 5)
  field(EGU, "keV")
  field(VAL, 0.0)
}

record(bo, "EPICS:energy:lock") {
  field(DESC, "lock hkl to mono?")
  field(ONAM, "locked")
  field(ZNAM, "unlocked")
  field(VAL, 0)
}