Merge pull request #1944 from klausschuch/pu/klausschuch/fix_clocks

Clarify the information flow of clocks

docs/2_2_common_mechanisms.adoc

@@ -283,7 +283,9 @@ All variables are listed in <<modelDescription.xml>> as elements of `<fmiModelDe
 
 They are identified with a unique handle called <<valueReference, value reference>>.
 
-The attribute <<causality>> defines the direction of the information flow with respect to the FMU (e.g. <<input>>, <<output>>, <<parameter>>).
+The attribute <<causality>> defines the direction of the information flow with respect to the FMU (e.g. <<input>>, <<output>>, <<parameter>>). +
+For Clocks the <<causality>> indicates the information flow of the activation of the Clock. +
+Only for triggered Clocks, the <<causality>> also indicates the information flow of the timing.
 
 Variables, except Clocks, may be scalar or multi-dimensional arrays.
 Clocks must always be scalar.
@@ -535,7 +537,11 @@ Input Clock::
 is a variable of type Clock with <<causality>> = <<input>>.
 In Model Exchange and Co-Simulation, when input Clocks tick, the importer will activate the input Clocks using <<fmi3SetClock>>.
 In Scheduled Execution, when input Clocks tick, the importer will activate the associated model partitions (but not the input Clocks) using <<fmi3ActivateModelPartition>>.
-While the importer is the source of the actual Clock activations, the timing of the Clocks is defined by the FMU, either through the <<modelDescription.xml>> or calling <<fmi3GetInterval>>, or by another Clock connected to a <<triggered>> input Clock.
+
+The importer is the source of the actual Clock activations of input Clocks.
+For time-based input Clocks, the timing is defined by the FMU, either through the <<modelDescription.xml>> or by the importer calling <<fmi3GetInterval>>.
+For <<triggered>> input clocks, the timing is determined by the importer.
+_[The timing could be given by a triggered output Clock, or a time-based input Clock of a connected FMU, or any other source.]_
 
 Output Clock::
 [[outputClock, `output Clock`]]

docs/2_4_common_schema.adoc

@@ -965,8 +965,11 @@ If a <<structuralParameter,`structural parameter`>> is referenced in <<Dimension
 The `min` attribute might still be 0.
 
 The default of <<causality>> is <<local>>. +
-A continuous-time <<state>> or an event indicator must have <<causality>> = <<local>> or <<output>>, see also <<ModelStructure>>. +
-The causality of variables of type <<Clock>> must be either <<input>>, <<output>> or <<local>>.
+A continuous-time <<state>> or an event indicator must have <<causality>> = <<local>> or <<output>>, see also <<ModelStructure>>.
+
+The causality of variables of type <<Clock>> must be either <<input>>, <<output>> or <<local>>. +
+For Clocks the <<causality>> indicates the information flow of the activation of the Clock. +
+Only for triggered Clocks, the <<causality>> also indicates the information flow of the timing.
 
 |`variability`
 |