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

--  This file is a part of the LEON VHDL model

--  Copyright (C) 1999  European Space Agency (ESA)

--

--  This library is free software; you can redistribute it and/or

--  modify it under the terms of the GNU Lesser General Public

--  License as published by the Free Software Foundation; either

--  version 2 of the License, or (at your option) any later version.

--

--  See the file COPYING.LGPL for the full details of the license.

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

-- Entity:      dcom_uart

-- File:        dcom_uart.vhd

-- Author:      Jiri Gaisler - Gaisler Research

-- Description: Asynchronous UART with baud-rate detection.

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

library IEEE;

use IEEE.std_logic_1164.all;

use IEEE.std_logic_unsigned."+";

use IEEE.std_logic_unsigned."-";

use IEEE.std_logic_unsigned.">";

use work.leon_target.all;

use work.leon_config.all;

use work.leon_iface.all;

use work.macro.all;

use work.amba.all;

--pragma translate_off

use ieee.std_logic_unsigned.conv_integer;

use STD.TEXTIO.all;

--pragma translate_on

entity dcom_uart is

  port (

    rst    : in  std_logic;

    clk    : in  clk_type;

    apbi   : in  apb_slv_in_type;

    apbo   : out apb_slv_out_type;

    uarti  : in  dcom_uart_in_type;

    uarto  : out dcom_uart_out_type

  );

end;

architecture rtl of dcom_uart is

type rxfsmtype is (idle, startbit, data, stopbit);

type txfsmtype is (idle, data, stopbit);

type uartregs is record

  rxen          :  std_logic;   -- receiver enabled

  dready        :  std_logic;   -- data ready

  rsempty       :  std_logic;   -- receiver shift register empty (internal)

  tsempty       :  std_logic;   -- transmitter shift register empty

  thempty       :  std_logic;   -- transmitter hold register empty

  break         :  std_logic;   -- break detected

  ovf           :  std_logic;   -- receiver overflow

  frame         :  std_logic;   -- framing error

  rhold         :  std_logic_vector(7 downto 0);

  rshift        :  std_logic_vector(7 downto 0);

  tshift        :  std_logic_vector(10 downto 0);

  thold         :  std_logic_vector(7 downto 0);

  txstate       :  txfsmtype;

  txclk         :  std_logic_vector(2 downto 0);  -- tx clock divider

  txtick        :  std_logic;   -- tx clock (internal)

  rxstate       :  rxfsmtype;

  rxclk         :  std_logic_vector(2 downto 0); -- rx clock divider

  rxdb          :  std_logic;   -- rx data filtering buffer

  rxtick        :  std_logic;   -- rx clock (internal)

  tick          :  std_logic;   -- rx clock (internal)

  scaler        :  std_logic_vector(17 downto 0);

  brate         :  std_logic_vector(17 downto 0);

  tcnt          :  std_logic_vector(1 downto 0); -- autobaud counter

  rxdb2         :  std_logic;   -- delayed rx data

  rxf           :  std_logic_vector(7 downto 0); --  rx data filtering buffer

  fedge         :  std_logic;   -- rx falling edge

end record;

signal r, rin : uartregs;

begin

  uartop : process(rst, r, apbi, uarti )

  variable rdata : std_logic_vector(31 downto 0);

  variable scaler : std_logic_vector(17 downto 0);

  variable rxclk, txclk : std_logic_vector(2 downto 0);

  variable rxd : std_logic;

  variable v : uartregs;

  begin

    v := r;

    v.txtick := '0'; v.rxtick := '0'; v.tick := '0'; rdata := (others => '0');

-- scaler

-- pragma translate_off

    if not is_x(r.scaler) then          -- avoid warnings at reset time

-- pragma translate_on

      if r.tcnt = "11" then

        scaler := r.scaler - 1;

      else

        scaler := r.scaler + 1;

      end if;

-- pragma translate_off

    end if;

-- pragma translate_on

    v.rxdb2 := r.rxdb;

    if r.tcnt /= "11" then

      if (r.rxdb2 and not r.rxdb) = '1' then v.fedge := '1'; end if;

      if (r.fedge) = '1' then

        v.scaler := scaler;

        if (r.scaler(17) and not r.scaler(16)) = '1' then

          v.fedge := '0'; v.tcnt := "00";

          v.scaler := "111111111111111011";

        end if;

      end if;

      if (r.rxdb2 and r.fedge and not r.rxdb) = '1' then

        if ieee.std_logic_unsigned.">"(r.brate(17 downto 4),r.scaler(17 downto 4)) then

          v.brate := r.scaler; v.tcnt := "00";

        end if;

        v.scaler := "111111111111111011";

        if (r.brate(17 downto 4) = r.scaler(17 downto 4)) then

          v.tcnt := r.tcnt + 1;

          if r.tcnt = "10" then

            v.brate := "0000" & r.scaler(17 downto 4);

            v.scaler := v.brate; v.rxen := '1';

          end if;

        end if;

      end if;

    else

      if (r.break and r.rxdb2) = '1' then

        v.scaler := "111111111111111011";

        v.brate := (others => '1'); v.tcnt := "00";

        v.break := '0'; v.rxen := '0';

      end if;

    end if;

    if r.rxen = '1' then

      v.scaler := scaler;

      v.tick := scaler(15) and not r.scaler(15);

      if v.tick = '1' then v.scaler := r.brate; end if;

    end if;

-- read/write registers

    if uarti.read = '1' then

      v.dready := '0';

    end if;

    case apbi.paddr(3 downto 2) is

--    when "00" => 

--      rdata(7 downto 0) := r.rhold; 

--      if (apbi.psel and apbi.penable and (not apbi.pwrite)) = '1' then 

--      v.dready := '0';

--      end if;

    when "01" =>

      rdata(6 downto 0) := r.frame & '0' & r.ovf &

                r.break & r.thempty & r.tsempty & r.dready;

--pragma translate_off

      if DEBUGUART then rdata(2 downto 1) := "11"; end if;

--pragma translate_on

    when "10" =>

      rdata(1 downto 0) := (r.tcnt(1) or r.tcnt(0)) & r.rxen;

    when others =>

      rdata(17 downto 0) := r.brate;

    end case;

    if (apbi.psel and apbi.penable and apbi.pwrite) = '1' then

      case apbi.paddr(3 downto 2) is

      when "01" =>

        v.frame  := apbi.pwdata(6);

        v.ovf    := apbi.pwdata(4);

        v.break  := apbi.pwdata(3);

      when "10" =>

        v.tcnt   := apbi.pwdata(1) & apbi.pwdata(1);

        v.rxen   := apbi.pwdata(0);

      when "11" =>

        v.brate := apbi.pwdata(17 downto 0);

        v.scaler := apbi.pwdata(17 downto 0);

      when others =>

      end case;

    end if;

-- tx clock

-- pragma translate_off

    if not is_x(r.txclk) then           -- avoid warnings at reset time

-- pragma translate_on

      txclk := r.txclk + 1;

-- pragma translate_off

    else

      txclk := (others => 'X');

    end if;

-- pragma translate_on

    if r.tick = '1' then

      v.txclk := txclk;

      v.txtick := r.txclk(2) and not txclk(2);

    end if;

-- rx clock

-- pragma translate_off

    if not is_x(r.rxclk) then           -- avoid warnings at reset time

-- pragma translate_on

      rxclk := r.rxclk + 1;

-- pragma translate_off

    else

      rxclk := (others => 'X');

    end if;

-- pragma translate_on

    if r.tick = '1' then

      v.rxclk := rxclk;

      v.rxtick := r.rxclk(2) and not rxclk(2);

    end if;

-- filter rx data

    v.rxf := r.rxf(6 downto 0) & uarti.rxd;

    if ((r.rxf(7) & r.rxf(7) & r.rxf(7) & r.rxf(7) & r.rxf(7) & r.rxf(7) &

         r.rxf(7)) = r.rxf(6 downto 0))

    then v.rxdb := r.rxf(7); end if;

    rxd := r.rxdb;

-- transmitter operation

    case r.txstate is

    when idle =>        -- idle state

      if (r.txtick = '1') then v.tsempty := '1'; end if;

      if (r.rxen and (not r.thempty) and r.txtick) = '1' then

        v.tshift := "10" & r.thold & '0'; v.txstate := data;

        v.thempty := '1';

        v.tsempty := '0'; v.txclk := "00" & r.tick; v.txtick := '0';

      end if;

    when data =>        -- transmitt data frame

      if r.txtick = '1' then

        v.tshift := '1' & r.tshift(10 downto 1);

        if r.tshift(10 downto 1) = "1111111110" then

        v.tshift(0) := '1'; v.txstate := stopbit;

        end if;

      end if;

    when stopbit =>     -- transmitt stop bit

      if r.txtick = '1' then

        v.tshift := '1' & r.tshift(10 downto 1); v.txstate := idle;

      end if;

    end case;

-- writing of tx data register must be done after tx fsm to get correct

-- operation of thempty flag

    if uarti.write = '1' then

      v.thold := uarti.data(7 downto 0); v.thempty := '0';

    end if;

-- receiver operation

    case r.rxstate is

    when idle =>        -- wait for start bit

      if ((not r.rsempty) and not r.dready) = '1' then

        v.rhold := r.rshift; v.rsempty := '1'; v.dready := '1';

      end if;

      if (r.rxen and r.rxdb2 and (not rxd)) = '1' then

        v.rxstate := startbit; v.rshift := (others => '1'); v.rxclk := "100";

        if v.rsempty = '0' then v.ovf := '1'; end if;

        v.rsempty := '0'; v.rxtick := '0';

      end if;

    when startbit =>    -- check validity of start bit

      if r.rxtick = '1' then

        if rxd = '0' then

          v.rshift := rxd & r.rshift(7 downto 1); v.rxstate := data;

        else

          v.rxstate := idle;

        end if;

      end if;

    when data =>        -- receive data frame

      if r.rxtick = '1' then

        v.rshift := rxd & r.rshift(7 downto 1);

        if r.rshift(0) = '0' then

        v.rxstate := stopbit;

        end if;

      end if;

    when stopbit =>     -- receive stop bit

      if r.rxtick = '1' then

        if rxd = '1' then

          v.rsempty := '0';

          if v.dready = '0' then

            v.rhold := r.rshift; v.rsempty := '1'; v.dready := '1';

          end if;

        else

          if r.rshift = "00000000" then

            v.break := '1';              -- break

          else

            v.frame := '1';              -- framing error

          end if;

          v.rsempty := '1';

        end if;

        v.rxstate := idle;

      end if;

    end case;

-- reset operation

    if rst = '0' then

      v.frame := '0'; v.rsempty := '1';

      v.ovf := '0'; v.break := '0'; v.thempty := '1';

      v.tsempty := '1'; v.dready := '0'; v.fedge := '0';

      v.txstate := idle; v.rxstate := idle; v.tshift(0) := '1';

      v.scaler := "111111111111111011"; v.brate := (others => '1');

      v.rxen := '0'; v.tcnt := "00";

      v.txclk := (others => '0'); v.rxclk := (others => '0');

    end if;

-- update registers

    rin <= v;

-- drive outputs

    uarto.txd <= r.tshift(0);

    uarto.dready <= r.dready;

    uarto.tsempty <= r.tsempty;

    uarto.thempty <= r.thempty;

    uarto.lock <= r.tcnt(1) and  r.tcnt(0);

    uarto.enable <= r.rxen;

    uarto.data <= r.rhold;

    apbo.prdata <= rdata;

  end process;

  regs : process(clk)

  begin if rising_edge(clk) then r <= rin; end if; end process;

end;