Issue65 cdl spec tran

[mwetter]

This closes #65

[AntoineGautier]

@mwetter I corrected some typos in my commits. I add here some additional comments.

• (In the whole document, CDL is either expanded into Control Description Language or Controls Description Language.)
• §7.6.1
  • "unless a parameter is a structural parameter." What is the CDL syntax to flag a structural parameter?
  • "parameter assignment can only be literals (such as Real, Integer and Boolean) and arrays of literals." However expressions are also allowed. Should we add "and expressions involving literals" in the previous sentence?
  • Code snippets in §7.6.1.1 show parameter assignments using non literals e.g. uLow = pRel-25.
  • For Real and Integer, expressions involving >, >=, <, <=, ==, <> are allowed. That means that conditional assignments are allowed?
• §7.6.1.1
  • I understand that the rationale behind this use case is that if the control sequence developer has not specified a parameter as final then the control logic itself does not depend on a specific value of that parameter i.e. it is rather a suggested value and the relationship between the values of k, uLow and uHigh in the example is not essential for the sequence to work correctly. If that is correct (and useful) maybe we could integrate such a description of context in that §.
  • "the parameter hys.uLow has the unit not set because the assignment involves an expression." Maybe mention the motivation behind this rule i.e. unit conversion.
• §7.6.1.2
  • This is more a personal note to be sure I understand correctly... "the propagation of the parameter value is through block-diagram modeling only." That means that a connector variable must be assigned the value of the parameter in a first block (s.y = k in the example) and the value is then passed to another block by means of a connect statement involving an input connector variable declared in the other block (connect(s.y, someBlock.u)). In that other block no parameter can be assigned the value of the input variable (someBlock.u) as the variability differs. That means that parameter values can only be propagated with variables that can be connected together (the example from the previous § where one would make final k, uLow and uHigh is not supported). This is consistent with graphical control programming environments as described by Dave Robin where:
  • a wired connection is required for a value to be passed from one block to another,
  • virtual points allowing a value to be passed to different controllers through the network are then accessible in reading within each controller as standard hardware points (with a wired connection).
  • About the note regarding the use of CDL.Logical.Sources.SampleTrigger: this is only valid for that specific example where one would want to use the same sampling period between different blocks. For propagating generic parameter values (e.g. nominal values) among several blocks there is no available option.
• In those 2 previous §: in the pseudo-code snippets, should startValue rather be defaultValue?

[mwetter]

• [x] The condition "Connectors can only carry scalar variables" is not practical as we allow vectors of instances, which are needed for primary sequences for chiller plants.

[mwetter]

This will likely be replaced by https://github.com/lbl-srg/obc/pull/70