Add first architecture document. (#1988)

Author: janiversen

MAKE_RELEASE.rst

@@ -51,3 +51,11 @@ Prepare release on dev for new commits.
 ------------------------------------------------------------
 * Make pull request "prepare dev", with the following:
    * Update pymodbus/__init__.py with version number (__version__ X.Y.Zpre)
+
+
+------------------------------------------------------------
+Architecture documentation.
+------------------------------------------------------------
+* install graphviz
+* pyreverse -k -o jpg pymodbus 
+

README.rst

@@ -302,8 +302,8 @@ Test your changes::
    pytest
 
 
-Architecture
-^^^^^^^^^^^^
+Internals
+^^^^^^^^^
 
 There are no documentation of the architecture (help is welcome), but most classes and
 methods are documented:

doc/source/_static/examples.tgz

@@ -10,3 +10,6 @@ Pymodbus internals
    library/framer.rst
    library/constants.rst
    library/pymodbus.rst
+
+   library/architecture/architecture.rst
+

doc/source/_static/examples.zip

@@ -0,0 +1,28 @@
+Architecture
+=============
+
+The internal structure of pymodbus is a bit complicated, mostly due to the mixture of sync and async.
+
+The overall architecture can be viewed as:
+
+    Client classes (interface to applications)
+    mixin (interface with all requests defined as methods)
+    transaction (handles transactions and allow concurrent calls)
+    framers (add pre/post headers to make a valid package)
+    transport (handles actual transportation)
+
+    Server classes (interface to applications)
+    datastores (handles registers/values to be returned)
+    transaction (handles transactions and allow concurrent calls)
+    framers (add pre/post headers to make a valid package)
+    transport (handles actual transportation)
+
+In detail the packages can viewed as:
+
+.. image:: packages.png
+
+
+In detail the classes can be viewed as:
+
+.. image:: classes.png
+