Objective VHDL provides single inheritance for entity classes. The following example shows implementation of the counter class hierarchy with entity classes:
entity up_down_counter is new counter with
procedure count_down;
end up_down_counter;
entity address_counter is new counter with
procedure count_up;
end class address_counter;
The up_down_counter entity declares a new count_down method whereas the address_counter entity redeclares the count_up method.
The derived entities inherit from the parent entity counter:
- ports & generics
- attributes & methods
- other declarations & statements of parent entity
Implementation of architectures of derived entities:
architecture CounterArch of up_down_counter
is new CounterArch of Counter with
procedure count_down is
begin
load ( value - 1 );
end;
begin
end CounterArch;
architecture CounterArch of address_counter
is new CounterArch of Counter with
procedure count_up is
begin
load ( value + 4 );
end;
begin
end CounterArch;