make return value 'Done' unneccessary

'Done' was introduced in order to suppress unneccessary
duplicate updates. However, since super calls on access methods are
allowed, it is not nice when such a method returns Done, as this
is not automagically replaced by the current parameter value.
As a consequence:

- using Done is discouraged, but not (yet) removed in all code
- the 'omit_unchanged_within' property is moved from Module to an
  internal Parameter property 'update_unchanged'
- its default is moved from a SEC node property to generalConfig
- the 'update_unchanged' parameter property may be set to
  'never' for parameters where duplicate updates make no sense
- this property might be set to 'always', for measurements, where
  even unchanged values taken from HW should be transmitted

Change-Id: I2847c983ca09c2c4098e402edd08d0c96c3913f4
Reviewed-on: https://forge.frm2.tum.de/review/c/secop/frappy/+/30672
Tested-by: Jenkins Automated Tests <pedersen+jenkins@frm2.tum.de>
Reviewed-by: Markus Zolliker <markus.zolliker@psi.ch>

frappy/protocol/dispatcher.py

@@ -55,17 +55,15 @@ def make_update(modulename, pobj):
     if pobj.readerror:
         return (ERRORPREFIX + EVENTREPLY, '%s:%s' % (modulename, pobj.export),
                 # error-report !
-                [pobj.readerror.name, repr(pobj.readerror), dict(t=pobj.timestamp)])
+                [pobj.readerror.name, repr(pobj.readerror), {'t': pobj.timestamp}])
     return (EVENTREPLY, '%s:%s' % (modulename, pobj.export),
-            [pobj.export_value(), dict(t=pobj.timestamp)])
+            [pobj.export_value(), {'t': pobj.timestamp}])
 
 
 class Dispatcher:
     def __init__(self, name, logger, options, srv):
         # to avoid errors, we want to eat all options here
         self.equipment_id = options.pop('equipment_id', name)
-        # time interval for omitting updates of unchanged values
-        self.omit_unchanged_within = options.pop('omit_unchanged_within', 0.1)
         self.nodeprops = {}
         for k in list(options):
             self.nodeprops[k] = options.pop(k)
@@ -230,7 +228,7 @@ class Dispatcher:
         result = cobj.do(moduleobj, argument)
         if cobj.result:
             result = cobj.result.export_value(result)
-        return result, dict(t=currenttime())
+        return result, {'t': currenttime()}
 
     def _setParameterValue(self, modulename, exportedname, value):
         moduleobj = self.get_module(modulename)
@@ -253,7 +251,7 @@ class Dispatcher:
         # note: exceptions are handled in handle_request, not here!
         getattr(moduleobj, 'write_' + pname)(value)
         # return value is ignored here, as already handled
-        return pobj.export_value(), dict(t=pobj.timestamp) if pobj.timestamp else {}
+        return pobj.export_value(), {'t': pobj.timestamp} if pobj.timestamp else {}
 
     def _getParameterValue(self, modulename, exportedname):
         moduleobj = self.get_module(modulename)
@@ -272,7 +270,7 @@ class Dispatcher:
         # note: exceptions are handled in handle_request, not here!
         getattr(moduleobj, 'read_' + pname)()
         # return value is ignored here, as already handled
-        return pobj.export_value(), dict(t=pobj.timestamp) if pobj.timestamp else {}
+        return pobj.export_value(), {'t': pobj.timestamp} if pobj.timestamp else {}
 
     #
     # api to be called from the 'interface'