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The Runtime Organisation
The runtime organisation defines the interface between the generated
C++ code and the parallel kernel, and consists of a number of
C++ class definitions. These classes serve to raise the semantic
level of C++ to that of VHDL. In fact it is possible, although
cumbersome, to write a VHDL-like description in C++, using the runtime
environment. The advantages of the high level runtime organisation are that
we are able to develop the VHDL compiler with a minimum of effort.
The three most important classes are called Value, Signal and
Process. These are shown in more detail below.
The Value class offers a single datatype to represent every possible
VHDL type. This greatly simplifies the interface of the runtime
environment. Reference counting is used to implement a garbage
The Signal class is used to represent all VHDL signals. Scalar signals
contain the current value as an object of type Value. Composite signals
consist of an array of Signal.
The Process class implements concurrent processes. Process are
automatically suspended when they wait for signals, and they
are resumed as soon as the signals are updated. Processes are
implemented as light weight threads using a special library.