Schaltungsdesign mit VHDL

B Die Sprache VHDL
ARCHITECTURE demo OF queue IS
TYPE chain_element; -- unvollstaendige Dekl.
TYPE pointer IS ACCESS chain_element;
TYPE chain_element IS RECORD -- vollst. Deklaration
next_element : pointer;
element_data : integer;
END RECORD;
BEGIN
handle_queue : PROCESS (command)
VARIABLE empty_flag : boolean := true;
VARIABLE first, last, help : pointer := NULL;
BEGIN
CASE command IS
WHEN add_element =>
IF empty_flag THEN
first := NEW chain_element; last := first;
empty_flag := false;
ELSE
last.next_element := NEW chain_element;
last := last.next_element;
END IF;
last.element_data := value;
WHEN delete_element =>
IF empty_flag THEN
ASSERT false REPORT "Empty queue!" SEVERITY note;
ELSE
value
IF empty_flag THEN
ASSERT false REPORT "Empty queue!" SEVERITY note;
ELSE
value NULL;
END CASE;
END PROCESS;
END demo;
226 © G. Lehmann/B. Wunder/M. Selz