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--| Modular Oscilloscope

--| UNSL - Argentine

--|

--| Version: 0.01

--| Tested in: Actel APA300

--|-------------------------------------------------------------------------------------------------

--| Description:

--|     EPP - Wishbone bridge. 

--|       Convert 8 to 16 bits width data bus

--|-------------------------------------------------------------------------------------------------

--| File history:

--|   0.01  | mar-2009 | First release

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--| Copyright ® 2008, Facundo Aguilera.

--|

--| This VHDL design file is an open design; you can redistribute it and/or

--| modify it and/or implement it after contacting the author.

--| Wishbone Rev. B.3 compatible

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-- COMO USAR:

-- Puente entre un bus de datos de 8 bit (esclavo) y otro de 16 bit (maestro). cada dos acciones del

-- lado de 8 bit realiza una en en lado de 16. Posee un timer configurable con el que vuelve al 

-- estado inicial luego de sierto tiempo (ningun byte leido). También vuelve al estado inicial al 

-- hacer un cambio de dirección, por lo que puede realizarse una sincronización inicial haciendo un

-- cambio de dirección de escritura.

library IEEE;

use IEEE.STD_LOGIC_1164.all;

use IEEE.STD_LOGIC_ARITH.all;

use ieee.std_logic_unsigned.all;

use IEEE.numeric_std.all;

use work.eppwbn_pkg.all;

entity eppwbn_width_extension is

  generic (

    TIME_OUT_VALUE: integer  := 255;

    TIME_OUT_WIDTH: integer  := 8

  );

  port(

    -- Slave signals

    DAT_I_sl: in  std_logic_vector (7 downto 0);

    DAT_O_sl: out std_logic_vector (7 downto 0);

    ADR_I_sl: in  std_logic_vector (7 downto 0);

    CYC_I_sl: in  std_logic;

    STB_I_sl: in  std_logic;

    ACK_O_sl: out std_logic ;

    WE_I_sl:  in  std_logic;

    --  Master signals

    DAT_I_ma: in  std_logic_vector (15 downto 0);

    DAT_O_ma: out std_logic_vector (15 downto 0);

    ADR_O_ma: out std_logic_vector (7 downto 0);

    CYC_O_ma: out std_logic;

    STB_O_ma: out std_logic;

    ACK_I_ma: in  std_logic ;

    WE_O_ma:  out std_logic;

    -- Common signals

    RST_I: in std_logic;

    CLK_I: in std_logic

  );

end entity eppwbn_width_extension;

architecture arch_0 of eppwbn_width_extension is

  type StateType is (

          st_low,

          st_high

          );

        signal next_state, present_state: StateType;

  signal dat_reg, adr_reg: std_logic_vector (7 downto 0);  -- Almacena temporalmente las entradas

  signal timer, time_out_ref: std_logic_vector (TIME_OUT_WIDTH - 1 downto 0);

begin

  ADR_O_ma <= ADR_I_sl;

  time_out_ref <= conv_std_logic_vector(TIME_OUT_VALUE, TIME_OUT_WIDTH);

  P_state_comb: process(DAT_I_sl,CYC_I_sl,STB_I_sl,WE_I_sl,ACK_I_ma,present_state,ADR_I_sl,

                        DAT_I_ma,dat_reg,adr_reg,timer,time_out_ref)

  begin

    case present_state is

      -- Escritura: Señales de hadshake provistas por el módulo. Se guarda byte bajo.

      -- Lectura: Señales de hadshake provistas por fuente. Se guarda byte alto.

      when st_low =>

        WE_O_ma <= '0';

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

        DAT_O_sl <= DAT_I_ma(7 downto 0);

        if WE_I_sl = '1' then

          CYC_O_ma <= '0'; -- Esperar hasta recibir el proximo byte

          STB_O_ma <= '0';

          ACK_O_sl <= CYC_I_sl and STB_I_sl; -- Genera autorespuesta

        else

          CYC_O_ma <= CYC_I_sl;

          STB_O_ma <= STB_I_sl;

          ACK_O_sl <= ACK_I_ma;

        end if;

        if (CYC_I_sl = '1' and STB_I_sl = '1') and (WE_I_sl = '1' or ACK_I_ma = '1') then

          next_state <= st_high;

        else

          next_state <= st_low;

        end if;

      -- Escritura: Señales de hadshake provistas por fuentepor el módulo. 

      -- Lectura: Señales de hadshake provistas por el módulo. 

      when others =>

        WE_O_ma <= WE_I_sl;

        DAT_O_ma <= DAT_I_sl & dat_reg;

        DAT_O_sl <= dat_reg;

        if adr_reg = ADR_I_sl then

          if WE_I_sl = '1' then

            CYC_O_ma <= CYC_I_sl; -- Usa señales de la fuente

            STB_O_ma <= STB_I_sl;

            ACK_O_sl <= ACK_I_ma;

          else

            CYC_O_ma <= '0';

            STB_O_ma <= '0';

            ACK_O_sl <= CYC_I_sl and STB_I_sl; -- Genera autorespuesta

          end if;

        else

          CYC_O_ma <= '0';

          STB_O_ma <= '0';

          ACK_O_sl <= '0';

        end if;

        if  ((CYC_I_sl = '1' and STB_I_sl = '1') and (WE_I_sl /= '1' or ACK_I_ma = '1'))

        or ((CYC_I_sl = '1' and STB_I_sl = '1') and (ADR_I_sl /= adr_reg))

        or (timer >= time_out_ref) then

          next_state <= st_low;

        else

          next_state <= st_high;

        end if;

    end case;

  end process;

  P_state_clocked: process(RST_I,CLK_I,next_state,timer)

  begin

    if RST_I = '1' then

      present_state <= st_low;

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

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

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

    elsif CLK_I'event and CLK_I = '1' then

      -- Resgistrar los valores si va a cambir al estado st_high

      if next_state = st_high and present_state = st_low then

        adr_reg <= ADR_I_sl;

        if WE_I_sl = '1' then

          dat_reg <= DAT_I_sl; -- Guarda byte bajo

        else

          dat_reg <= DAT_I_ma(15 downto 8);

        end if;

      end if;

      -- Configuración del timer

      if present_state = st_high then

        timer <= timer + 1;

      else

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

      end if;

      -- Cambio de estado

      present_state <= next_state;

    end if;

  end process;

end architecture arch_0;