Is it possible to use synchronous process in functions?

Question

i=0;
If rising_edge (clk) then
y(i)<=x(i) ;
i=:i+1;
end if;

Is a block like above, possible in a function block? If it is not, is there any function-like sub-program style to achieve this?

Or is there any synthetizable 'for loop' usage instead of 'if statement'?

Answer 1

No, you can't have a clocked process inside a function. You can use a loop, though:

if rising_edge(clk) then
  for i in 0 to x'length - 1 loop
    y(i) <= x(i); -- or whatever operation
  end loop;
end if;

You can wrap the for-loop portion only in a function if you really want:

function f(x : std_logic_vector) return std_logic_vector is
  variable result : std_logic_vector(x'range);
begin
  for i in x'range loop
    result(i) := x(i); -- or whatever operation
  end loop;
  return result;
end function f;

if rising_edge(clk) then
  y <= f(x);
end if;

I'm assuming you want to do more than just assign bits, of course, or else you wouldn't need a loop or function at all.

Answer 2

You can use procedures:

  procedure SetBits(signal clk : in std_logic; signal y : out std_logic_vector(7 downto 0)) is
  begin
    for i in 7 downto 0 loop
      wait until (rising_edge(clk));
      y(i) <= '1';
    end loop;
  end procedure;

and then something like this

  sequential : process
  begin
    SetBits;
    wait;
  end process sequential;