34_readwrite.vhd

这是一个对于初学者很好的vhdl实验的一些例子,希望站长的支持哦

package p is
    attribute cycle_time:Time;
    attribute max_cycles:Integer;
    attribute clock_phases:Integer;
    attribute Integer_width:Integer;
    Type my_integer    is range -2**15 to 2**15-1;
    Type array_of_integer is array(1 to 16) of my_integer;
    Type my_integer_Vector is array(Natural range<>) of my_integer;
    FUNCTION wired_and (inputs : my_integer_Vector) RETURN my_integer;
end package p;
package body p is
    FUNCTION wired_and (inputs : my_integer_Vector) RETURN my_integer IS
    VARIABLE m:  my_integer:=0;
    BEGIN
         IF  inputs'Length=0 THEN
              RETURN 0;
         ELSE
              FOR i IN inputs'Range LOOP
                 IF inputs(i)>m THEN
                       m:=inputs(i);
                 END IF;  
              END LOOP;
              RETURN m;
         END IF; 
    END;
end p;
Use work.p.all;
entity e is
    port(bus1  : Inout wired_and my_integer;
            bus_ready : In Bit);
        attribute cycle_time of e : entity is 50 ns;
        attribute clock_phases of e : entity is 1;
end e;

architecture arch of e is

   begin
       p1:Process
            variable a :array_of_integer;
            variable max:my_integer;
            variable loop_time:time;
            variable i:my_integer;
         begin
       --read bus
       --read_bus(bus1,bus_ready,a)
    
        loop_time  :=Now;
        ll1:for i in 1 to 16 loop
             wait until bus_ready='1';
             a(i):=bus1;
        end loop ll1;
        assert (Now-loop_time)<=(16*e'cycle_time) --revised by dls
               report "loop took too long.";   
       --operate on a(modeled here just by a delay)
         wait for 10 ns;
       --find max(a)
         max:=a(1);
         ll2: for i in 2 to 16 loop
             if a(i)>max then max:=a(i);
             end if;
         end loop ll2;
       --bus gets max(a)
         bus1<=max after 50 ns;
         end process p1;
end arch;