--------------------------------------------------------------------------------
-- Differential Equation Benchmark
--------------------------------------------------------------------------------

PACKAGE diffeq_types IS
  SUBTYPE nat is integer;
END diffeq_types;

USE work.diffeq_types.all;

entity diffeq is
   port (Xinport: in nat;
         Yinport: in nat;
         Uinport: in nat;
         Aport  : in nat;
         DXport : in nat;
         Xoutport: out nat;
         Youtport: out nat;
         Uoutport: out nat;
         CLK : in bit);
end diffeq;

--============================================================
architecture diffeq of diffeq is
signal oldx, oldy, oldu : nat;
signal newx, newy, newu : nat;
begin
--============================================================
MAIN : process (CLK, Aport, DXport, Xinport, Yinport, Uinport)
  variable x_var, y_var, u_var, a_var, dx_var: nat;
  variable y1, t1,t2,t3,t4,t5,t6: nat;
  variable looping : bit;
begin
  if (CLK'event and CLK = '1') then 
    if (looping = '0') then
      x_var := Xinport;
      y_var := Yinport;
      u_var := Uinport;
      looping := '1';
    else
      x_var := newx;
      y_var := newy;
      u_var := newu;
    end if;
    a_var := Aport;
    dx_var := DXport;
    if (x_var < a_var) then
      t1 := u_var * dx_var;
      t2 := 3 * x_var;
      t3 := 3 * y_var;
      t4 := t1 * t2;
      t5 := dx_var * t3;
      t6 := u_var - t4;
      u_var := t6 - t5;
      y1 := u_var * dx_var;
      y_var := y_var + y1;
      x_var := x_var + dx_var;
      oldx <= x_var;
      oldy <= y_var;
      oldu <= u_var;
    else
      Xoutport <= x_var;
      Youtport <= y_var;
      Uoutport <= u_var;
      looping := '0';
    end if;
  end if;
end process;

--============================================================
SYNCH: process(CLK, oldx, oldy, oldu)
  begin
    if (CLK'event and CLK = '1') then
      newx <= oldx;
      newy <= oldy;
      newu <= oldu;
    end if;
  end process;

--============================================================
end diffeq;