---------------------------------------------------------------------------------                                                                           ----          X       X   XXXXXX    XXXXXX    XXXXXX    XXXXXX      X          ----          XX     XX  X      X  X      X  X      X  X           XX          ----          X X   X X  X         X      X  X      X  X          X X          ----          X  X X  X  X         X      X  X      X  X         X  X          ----          X   X   X  X          XXXXXX   X      X   XXXXXX      X          ----          X       X  X         X      X  X      X         X     X          ----          X       X  X         X      X  X      X         X     X          ----          X       X  X      X  X      X  X      X         X     X          ----          X       X   XXXXXX    XXXXXX    XXXXXX    XXXXXX      X          ----                                                                           ----                                                                           ----                       O R E G A N O   S Y S T E M S                       ----                                                                           ----                            Design & Consulting                            ----                                                                           -----------------------------------------------------------------------------------                                                                           ----         Web:           http://www.oregano.at/                             ----                                                                           ----         Contact:       mc8051@oregano.at                                  ----                                                                           -----------------------------------------------------------------------------------                                                                           ----  MC8051 - VHDL 8051 Microcontroller IP Core                               ----  Copyright (C) 2001 OREGANO SYSTEMS                                       ----                                                                           ----  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 2.1 of the License, or (at your option) any later version.       ----                                                                           ----  This library is distributed in the hope that it will be useful,          ----  but WITHOUT ANY WARRANTY; without even the implied warranty of           ----  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU        ----  Lesser General Public License for more details.                          ----                                                                           ----  Full details of the license can be found in the file LGPL.TXT.           ----                                                                           ----  You should have received a copy of the GNU Lesser General Public         ----  License along with this library; if not, write to the Free Software      ----  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA  ----                                                                           ---------------------------------------------------------------------------------------         Author:                 Roland H鰈ler----         Filename:               mc8051_siu_rtl.vhd----         Date of Creation:       Mon Aug  9 12:14:48 1999----         Version:                $Revision: 1.8 $----         Date of Latest Version: $Date: 2002/09/05 11:16:08 $------         Description: Serial interface unit for the mc8051 microcontroller.---------------------------------------------------------------------------------------architecture rtl of mc8051_siu is  signal s_rxpre_count  : unsigned(5 downto 0);  -- Receive prescaler  signal s_txpre_count  : unsigned(5 downto 0);  -- Transmit prescaler  signal s_m0_shift_en  : std_logic;             -- masks out every sixteenth                                                 -- rising edge of clk  signal s_m2_rxshift_en  : std_logic;           -- mode 2 shift enable  signal s_m13_rxshift_en : std_logic;           -- mode 1 and 3 shift enable  signal s_m2_txshift_en  : std_logic;           -- mode 2 shift enable  signal s_m13_txshift_en : std_logic;           -- mode 1 and 3 shift enable  signal s_ff0          : std_logic;             -- flipflop for edge dedection  signal s_ff1          : std_logic;             -- flipflop for edge dedection  signal s_tf           : std_logic;             -- synchronised timer flag  signal s_mode         : unsigned(1 downto 0);  -- mode  signal s_sm2          : std_logic;             -- multi processor comm. bit  signal s_detect       : std_logic;             -- indicates start of recept.   signal s_ren          : std_logic;             -- receive enable  signal s_rxd_val      : std_logic;             -- received data bit  signal s_txdm0        : std_logic;             -- shift clock for m0  signal s_ri           : std_logic;             -- external receive interrupt   signal s_trans        : std_logic;             -- enable transmission   signal s_recv_done    : std_logic;             -- receive interrupt  signal s_tran_done    : std_logic;             -- transmit interrupt  signal s_rb8          : std_logic;             -- 8th data bit  signal s_tb8          : std_logic;             -- 8th data bit  signal s_recv_state   : unsigned(3 downto 0);  -- state reg. of receive unit  signal s_tran_state   : unsigned(3 downto 0);  -- state reg. of transmit unit  signal s_rxd_ff0      : std_logic;             -- sample flip-flop  signal s_rxd_ff1      : std_logic;             -- sample flip-flop  signal s_rxd_ff2      : std_logic;             -- sample flip-flop  signal s_det_ff0      : std_logic;             -- rec. detect flip-flop  signal s_det_ff1      : std_logic;             -- rec. detect flip-flop  signal s_tran_sh      : unsigned(10 downto 0); -- transmission shift register  signal s_recv_sh      : unsigned(7 downto 0);  -- reception shift register  signal s_recv_buf     : unsigned(7 downto 0);  -- reception buffer register  signal s_rxm13_ff0    : std_logic;             -- generates an enable singal  signal s_rxm13_ff1    : std_logic;             -- generates an enable singal  signal s_txm13_ff0    : std_logic;             -- generates an enable singal  signal s_txm13_ff1    : std_logic;             -- generates an enable singal  begin                 -- architecture rtl      s_mode(1) <= scon_i(4);               -- defines the 4 operating modes  s_mode(0) <= scon_i(3);   s_ren  <= scon_i(1);                  -- receive enable  s_sm2  <= scon_i(2);                  -- 1 time or half time baud rate  s_tb8  <= scon_i(0);                  -- 9th data bit for transmission  s_ri   <= scon_i(5);                  -- the receive interrupt bit of the                                        -- control unit  sbuf_o <= std_logic_vector(s_recv_buf);  -- the receive buffer output  scon_o(0) <= s_recv_done;             -- set when reception is completed  scon_o(1) <= s_tran_done;             -- set when transmission is completed  scon_o(2) <= s_rb8;                   -- 9th data bit of reception  -------------------------------------------------------------------------------  -- The two flip flops are updated every rising clock edge of clk.  -- If a rising edge  -- on the port tf_i is dedected the signal s_tf is set to 1 for one period.  --  -- The transmission start signal s_trans is generated and held high till  -- the statemachine has been launched with its first shift.  --  -- The shift clock for mode0 is generated. It toggles with the half  -- s_m0_shift_en rate.    s_tf <= '1' when (s_ff0 = '1' and s_ff1 = '0') else '0';        p_sample_tf: process (clk,                        reset)          begin      if reset = '1' then        s_ff0 <= '0';        s_ff1 <= '0';        s_trans <= '0';      else        if clk'event and clk = '1' then          s_ff0 <= tf_i;          s_ff1 <= s_ff0;                    if trans_i = '1' then            s_trans <= '1';          else            case s_mode is              when ("00") =>                if s_m0_shift_en = '1' then                  s_trans <= '0';                end if;              when ("01") =>                 if s_m13_txshift_en = '1' then                  s_trans <= '0';                end if;              when ("10") =>                 if s_m2_txshift_en = '1' then                  s_trans <= '0';                end if;              when others =>                 if s_m13_txshift_en = '1' then                  s_trans <= '0';                end if;            end case;          end if;        end if;          end if;      end process p_sample_tf;      -------------------------------------------------------------------------------  -- The register s_rxpre_count is driven with the system clock clk. So a  -- good enable signal (which is stable when clk has its rising edge) can be  -- derived to mask out every pulse of clk needed.  -- s_m0_shift_en activates every sixteenth clock cycle  -- s_m2_shift_en activates baud rates of 1/32 or 1/64 the clock frequenzy  -- depending on signal smod_i  -- s_m13_shift_en activates baud rates depending on timer/counter1 flag        s_m0_shift_en <= '1' when s_txpre_count(3 downto 0) = conv_unsigned(15,5)                   else '0';        s_m2_rxshift_en <= '1' when (s_rxpre_count(4 downto 0) = conv_unsigned(31,5)                               and smod_i = '1') or                              (s_rxpre_count = conv_unsigned(63,6)                               and smod_i = '0')                   else '0';  s_m13_rxshift_en <= '1' when s_rxm13_ff0 = '1' and s_rxm13_ff1 = '0'                      else '0';  s_m2_txshift_en <= '1' when (s_txpre_count(4 downto 0) = conv_unsigned(31,5)                               and smod_i = '1') or                              (s_txpre_count = conv_unsigned(63,6)                               and smod_i = '0')                   else '0';  s_m13_txshift_en <= '1' when s_txm13_ff0 = '1' and s_txm13_ff1 = '0'                      else '0';        p_divide_clk: process (clk, reset)        begin      if reset = '1' then        s_rxpre_count <= conv_unsigned(0,6);        s_txpre_count <= conv_unsigned(0,6);        s_rxm13_ff0 <= '0';        s_rxm13_ff1 <= '0';        s_txm13_ff0 <= '0';        s_txm13_ff1 <= '0';      else        if clk'event and clk='1' then                      s_rxm13_ff1 <= s_rxm13_ff0;          s_txm13_ff1 <= s_txm13_ff0;                    if smod_i = '1' then            if s_rxpre_count(3 downto 0) = conv_unsigned(15,4) then              s_rxm13_ff0 <= '1';            else              s_rxm13_ff0 <= '0';            end if;          else            if s_rxpre_count(4 downto 0) = conv_unsigned(31,5) then              s_rxm13_ff0 <= '1';            else              s_rxm13_ff0 <= '0';            end if;                        end if;                       if smod_i = '1' then            if s_txpre_count(3 downto 0) = conv_unsigned(15,4) then              s_txm13_ff0 <= '1';            else              s_txm13_ff0 <= '0';            end if;          else            if s_txpre_count(4 downto 0) = conv_unsigned(31,5) then              s_txm13_ff0 <= '1';            else              s_txm13_ff0 <= '0';            end if;                        end if;                      if trans_i = '1' then            s_txpre_count <= conv_unsigned(0,6);          else            if s_mode=conv_unsigned(0,2) or s_mode=conv_unsigned(2,2) then               s_txpre_count <= s_txpre_count + conv_unsigned(1,1);            else              if s_tf = '1' then                s_txpre_count <= s_txpre_count + conv_unsigned(1,1);                end if;            end if;                        end if;          if s_detect = '1' then            s_rxpre_count <= conv_unsigned(0,6);          else            if s_mode=conv_unsigned(0,2) or s_mode=conv_unsigned(2,2) then               s_rxpre_count <= s_rxpre_count + conv_unsigned(1,1);            else              if s_tf = '1' then                s_rxpre_count <= s_rxpre_count + conv_unsigned(1,1);                end if;            end if;                        end if;        end if;      end if;      end process p_divide_clk;-------------------------------------------------------------------------------  -- This section samples the serial input for data detection, that is a  -- 1-to-0 transition at rxd in state "0000".  -- In all other states this unit reads the data bits depending on the baud  -- rate. In mode0 this section is not active.  s_detect <= '1' when s_det_ff0 = '0' and s_det_ff1 = '1' else '0';   s_rxd_val <= '1' when (s_rxd_ff0 = '1' and s_rxd_ff1 = '1') or                        (s_rxd_ff0 = '1' and s_rxd_ff2 = '1') or                        (s_rxd_ff1 = '1' and s_rxd_ff2 = '1') else '0';                 p_sample_rx: process (clk,                        reset)      begin    if reset = '1' then      s_rxd_ff0 <= '0';      s_rxd_ff1 <= '0';      s_rxd_ff2 <= '0';      s_det_ff0 <= '0';      s_det_ff1 <= '0';    else      if clk'event and clk='1' then                  if s_recv_state = conv_unsigned(0,4) then   -- state "0000" means          if s_ren = '1' then                       -- to listen for a 1 to 0