datapath_pack_body.vhd

design compile synthesis user guide

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-- Package body for DATAPATH functions and types
-- RTL Analyzer tutorial design
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-- Revision 1.4  1998/06/08  dannyb
-- format
--
-- Revision 1.3  1997/03/06  baldrik
-- none
--
-- Revision 1.2  1997/02/08  baldrik
-- use UNSIGNED for arithmetic
--
-- Revision 1.1  1997/02/07  baldrik
-- Initial revision
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Library IEEE;
use IEEE.Std_Logic_1164.all;
use IEEE.Std_Logic_arith.all;
use IEEE.Std_Logic_unsigned.all;

package body DATAPATH is

  function datapath ( POINTER    : in  POINT_TYPE;
                      ADDR       : in  ADDR_TYPE) return
                      CNT_TYPE is

    constant P_TOP : POINT_TYPE := 
      std_logic_vector(CONV_UNSIGNED(128, POINT_width));
    constant C_ZERO: CNT_TYPE := 
      std_logic_vector(CONV_UNSIGNED(0, CNT_width));
    constant C_ONE : CNT_TYPE := 
      std_logic_vector(CONV_UNSIGNED(1, CNT_width));
    constant C_TWO : CNT_TYPE := 
      std_logic_vector(CONV_UNSIGNED(2, CNT_width));

    variable X, 
             D    : ADDR_TYPE;
    variable A, 
             B,
             C    : CNT_TYPE;
    
begin
  X := ("00000000" & 
        (P_TOP - POINTER));
  
  D := (ADDR  - X);
  
  if  (X >= ADDR ) then
    A := C_ZERO;
  else -- A = D(10:0)
    for i in CNT_width -1 downto 0 loop        
      A(i) := D(i);
    end loop;          
  end if;
  
  if  (X >= ADDR ) then
    C := C_ZERO;
  else
    for i in POINT_width -1 downto 0 loop
      C(i) := D(i);
    end loop;
  end if;
  
  if (C = C_ZERO ) then
    B := C_ONE;
  else
    B := C_TWO;
  end if;
    
  return (A + B);

end datapath; -- function


end DATAPATH; -- package body