Subversion Repositories artificial_neural_network

----------------------------------------------------------------------------------

-- Company: CEI

-- Engineer: Enrique Herrero

--

-- Create Date:

-- Design Name: Configurable ANN

-- Module Name: af_sigmoid - Behavioral

-- Project Name:

-- Target Devices:

-- Tool versions:

-- Description: Sigmoid activation function implemented as a Look-Up-Table (LUT).

--

-- Dependencies:

--

-- Revision:

-- Revision 0.01 - File Created

-- Revision 1 - David Aledo

-- Additional Comments:

--

----------------------------------------------------------------------------------

library IEEE;

use IEEE.STD_LOGIC_1164.ALL;

use ieee.numeric_std.ALL;

use ieee.math_real.all;

entity af_sigmoid is

   generic

   (

      Nbit : natural := 8

   );

   port

   (

      reset   : in  std_logic;

      clk     : in  std_logic;

      run_in  : in  std_logic; -- Start and input data validation

      inputs  : in  std_logic_vector(Nbit-1 downto 0); -- Input data

      run_out : out std_logic; -- Output data validation, run_in for the next layer

      outputs : out std_logic_vector(Nbit-1 downto 0) -- Output data

   );

end af_sigmoid;

architecture Behavioral of af_sigmoid is

   -- Definition of internal modules, constants, signals, etc...

   -- Sigmoid parameters:

   constant f0 : real := 1.0; -- Slope at the origin

   constant fr : real := 2.0; -- fr = fmax - fmin

   signal dataIn: integer range (2**Nbit-1) downto 0; -- To convert std_logic_vector input to integer index for the LUT

   type table_t is array(0 to (2**Nbit)-1) of std_logic_vector(Nbit-1 downto 0); -- LUT type

-- Function Sigmoidal: generates the Look-Up-Table for the sigmoid activation function:

-- margin: maximun value of x.

   function Sigmoidal(margin:real;Nbit:natural) return table_t is

         variable scale,x,y,w,t: real;

         variable u: integer;

         variable fbits: std_logic_vector(Nbit-1 downto 0);

         variable table: table_t;

      begin

         scale := (2.0*margin)/(2.0**Nbit);   -- Calculates gap between to points

         x := -margin;

         for idx in -(2**(Nbit-1)) to (2**(Nbit-1))-1 loop

            y := (fr/(1.0+exp(((-4.0*f0)/fr)*x)))-(fr/2.0);

            w := y*(2.0**(Nbit-1));           -- Shifts bits to the left

            t := round(w);

            u := integer(t);

            fbits := std_logic_vector(to_signed(u,Nbit));

            table(to_integer(to_unsigned(idx+(2**Nbit),Nbit))):= fbits;

            x := x+scale;

         end loop;

         return table;

   end Sigmoidal;

   signal Table: table_t := Sigmoidal(1.0,Nbit); -- Generation of the LUT (at synthesis time)

begin

   -- Description of the activation function

   dataIn <= to_integer(signed(inputs));

   Activation: process(clk,reset)

      begin

         if clk'event and clk = '1' then

            if reset = '1' then

               run_out <= '0';

               outputs <= (others => '0');

            else

               if run_in = '1' then

                  run_out <='1';

                  outputs <=Table(dataIn); -- Assigns output value from the LUT

               else

                  run_out <='0';

               end if;

            end if;

         end if;

    end process;

end Behavioral;