Processes

Each VHDL process is transformed into a corresponding C++ class. All named entities^9.1 defined within the declarative section of the process are converted into class members. Additionally, some special variables store internal process information. I.e. the process class contains a pointer to the architecture-entity instance the process belongs to. In detail there are three kind of class variables:

• Variables which represent named entities defined within the declarative region of a process (i.e. VHDL process variables, VHDL constants ...).
• Variables which are copies of corresponding objects defined in the entity-architecture class. This mechanism avoids unnecessary accesses operations on the data part of the corresponding architecture-entity instance. E.g. a VHDL signal declared within the declarative region of an architecture is transformed into a variable of the corresponding architecture class. Unfortunately, as each process is transformed into a separate process class, read operations of a process on the signal require at least four memory access operations. One operation to access the data part of the entity-architecture instance, another operation to read the actual sig_info pointer, a third operation to get the reader pointer from the sig_info instance, and finally a last read operation to get the value of the signal. To provide direct access on the signal data (reader) a pointer to the reader value is added to the process class. Hence, each read operation of the process on this signal can be done directly.

• Internal process variables, i.e. a pointer referencing the architecture-entity instance or pointers to driver_info instances.

Each process class has three member functions. A constructor, a destructor and a function to execute the process code. The constructor elaborates the declaration part of the process. Additionally, all copies of architecture-entity objects are initialised. The destructor is called if a process suspends forever.

All process classes are derived from the base class process_base. The base class includes all informations which are common to all process classes.