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

-- Title      : UART

-- Project    : UART

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

-- File        : Uart.vhd

-- Author      : Philippe CARTON 

--               (pc@microsystemes.com / philippe.carton2@libertysurf.fr)

-- Organization: Microsystemes

-- Created     : 15/12/2001

-- Last update : 28/12/2001

-- Platform    : Foundation 3.1i

-- Simulators  : Foundation logic simulator

-- Synthesizers: Foundation Synopsys

-- Targets     : Xilinx Spartan

-- Dependency  : IEEE std_logic_1164, Rxunit.vhd, Txunit.vhd, utils.vhd

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

-- Description: Uart (Universal Asynchronous Receiver Transmitter) for SoC.

--    Wishbone compatable.

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

-- Copyright (c) notice

--    This core adheres to the GNU public license 

--

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

-- Revisions       :

-- Revision Number :

-- Version         :

-- Date    :

-- Modifier        : name <email>

-- Description     :

--

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

library ieee;

   use ieee.std_logic_1164.all;

entity UART is

  generic(BRDIVISOR: INTEGER range 0 to 65535 := 130); -- Baud rate divisor

  port (

-- Wishbone signals

     WB_CLK_I : in  Std_Logic;  -- clock

     WB_RST_I : in  Std_Logic;  -- Reset input

     WB_ADR_I : in  Std_Logic_Vector(1 downto 0); -- Adress bus          

     WB_DAT_I : in  Std_Logic_Vector(7 downto 0); -- DataIn Bus

     WB_DAT_O : out Std_Logic_Vector(7 downto 0); -- DataOut Bus

     WB_WE_I  : in  Std_Logic;  -- Write Enable

     WB_STB_I : in  Std_Logic;  -- Strobe

     WB_ACK_O : out Std_Logic;  -- Acknowledge

-- process signals     

     IntTx_O  : out Std_Logic;  -- Transmit interrupt: indicate waiting for Byte

     IntRx_O  : out Std_Logic;  -- Receive interrupt: indicate Byte received

     BR_Clk_I : in  Std_Logic;  -- Clock used for Transmit/Receive

     TxD_PAD_O: out Std_Logic;  -- Tx RS232 Line

     RxD_PAD_I: in  Std_Logic);  -- Rx RS232 Line     

end entity;

-- Architecture for UART for synthesis

architecture Behaviour of UART is

  component Counter is

  generic(COUNT: INTEGER range 0 to 65535); -- Count revolution

  port (

     Clk      : in  Std_Logic;  -- Clock

     Reset    : in  Std_Logic;  -- Reset input

     CE       : in  Std_Logic;  -- Chip Enable

     O        : out Std_Logic); -- Output  

  end component;

  component RxUnit is

  port (

     Clk    : in  Std_Logic;  -- system clock signal

     Reset  : in  Std_Logic;  -- Reset input

     Enable : in  Std_Logic;  -- Enable input

     ReadA  : in  Std_logic;  -- Async Read Received Byte

     RxD    : in  Std_Logic;  -- RS-232 data input

     RxAv   : out Std_Logic;  -- Byte available

     DataO  : out Std_Logic_Vector(7 downto 0)); -- Byte received

  end component;

  component TxUnit is

  port (

     Clk    : in  Std_Logic;  -- Clock signal

     Reset  : in  Std_Logic;  -- Reset input

     Enable : in  Std_Logic;  -- Enable input

     LoadA  : in  Std_Logic;  -- Asynchronous Load

     TxD    : out Std_Logic;  -- RS-232 data output

     Busy   : out Std_Logic;  -- Tx Busy

     DataI  : in  Std_Logic_Vector(7 downto 0)); -- Byte to transmit

  end component;

  signal RxData : Std_Logic_Vector(7 downto 0); -- Last Byte received

  signal TxData : Std_Logic_Vector(7 downto 0); -- Last bytes transmitted

  signal SReg   : Std_Logic_Vector(7 downto 0); -- Status register

  signal EnabRx : Std_Logic;  -- Enable RX unit

  signal EnabTx : Std_Logic;  -- Enable TX unit

  signal RxAv   : Std_Logic;  -- Data Received

  signal TxBusy : Std_Logic;  -- Transmiter Busy

  signal ReadA  : Std_Logic;  -- Async Read receive buffer

  signal LoadA  : Std_Logic;  -- Async Load transmit buffer

  signal Sig0   : Std_Logic;  -- gnd signal

  signal Sig1   : Std_Logic;  -- vcc signal  

  begin

  sig0 <= '0';

  sig1 <= '1';

  Uart_Rxrate : Counter -- Baud Rate adjust

     generic map (COUNT => BRDIVISOR)

     port map (BR_CLK_I, sig0, sig1, EnabRx);

  Uart_Txrate : Counter -- 4 Divider for Tx

     generic map (COUNT => 4)

     port map (BR_CLK_I, Sig0, EnabRx, EnabTx);

  Uart_TxUnit : TxUnit port map (BR_CLK_I, WB_RST_I, EnabTX, LoadA, TxD_PAD_O, TxBusy, TxData);

  Uart_RxUnit : RxUnit port map (BR_CLK_I, WB_RST_I, EnabRX, ReadA, RxD_PAD_I, RxAv, RxData);

  IntTx_O <= not TxBusy;

  IntRx_O <= RxAv;

  SReg(0) <= not TxBusy;

  SReg(1) <= RxAv;

  -- Implements WishBone data exchange.

  -- Clocked on rising edge. Synchronous Reset RST_I

  WBctrl : process(WB_CLK_I, WB_RST_I, WB_STB_I, WB_WE_I, WB_ADR_I)

  variable StatM : Std_Logic_Vector(4 downto 0);

  begin

     if Rising_Edge(WB_CLK_I) then

        if (WB_RST_I = '1') then

           ReadA <= '0';

           LoadA <= '0';

        else

           if (WB_STB_I = '1' and WB_WE_I = '1' and WB_ADR_I = "00") then -- Write Byte to Tx

              TxData <= WB_DAT_I;

              LoadA <= '1';   -- Load signal        

           else LoadA <= '0';

           end if;

           if (WB_STB_I = '1' and WB_WE_I = '0' and WB_ADR_I = "00") then -- Read Byte from Rx

              ReadA <= '1';   -- Read signal

           else ReadA <= '0';

           end if;

        end if;

     end if;

  end process;

  WB_ACK_O <= WB_STB_I;

  WB_DAT_O <=

     RxData when WB_ADR_I = "00" else  -- Read Byte from Rx

     SReg when WB_ADR_I = "01" else    -- Read Status Reg

     X"00";

end Behaviour;