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--==============================================================================

--                                                                             |

--    Project: IIC Multiple Bus Controller (IICMB)                             |

--                                                                             |

--    Module:  Byte layer FSM (master mode).                                   |

--    Version:                                                                 |

--             1.0,   April 29, 2016                                           |

--                                                                             |

--    Author:  Sergey Shuvalkin, (sshuv2@opencores.org)                        |

--                                                                             |

--==============================================================================

--==============================================================================

-- Copyright (c) 2016, Sergey Shuvalkin                                        |

-- All rights reserved.                                                        |

--                                                                             |

-- Redistribution and use in source and binary forms, with or without          |

-- modification, are permitted provided that the following conditions are met: |

--                                                                             |

-- 1. Redistributions of source code must retain the above copyright notice,   |

--    this list of conditions and the following disclaimer.                    |

-- 2. Redistributions in binary form must reproduce the above copyright        |

--    notice, this list of conditions and the following disclaimer in the      |

--    documentation and/or other materials provided with the distribution.     |

--                                                                             |

-- THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" |

-- AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE   |

-- IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE  |

-- ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE    |

-- LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR         |

-- CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF        |

-- SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS    |

-- INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN     |

-- CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)     |

-- ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE  |

-- POSSIBILITY OF SUCH DAMAGE.                                                 |

--==============================================================================

library ieee;

use ieee.std_logic_1164.all;

use ieee.numeric_std.all;

use work.iicmb_pkg.all;

use work.iicmb_int_pkg.all;

--==============================================================================

entity mbyte is

  generic

  (

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

    g_bus_num   :       positive range 1 to 16 := 1;               -- Number of separate I2C buses

    g_f_clk     :       real                   := 100000.0         -- Frequency of system clock 'clk' (in kHz)

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

  );

  port

  (

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

    clk         : in    std_logic;                                 -- Clock

    s_rst       : in    std_logic;                                 -- Synchronous reset (active high)

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

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

    captured    :   out std_logic := '0';                          -- 'Bus is captured' indication (captured = high)

    busy        : in    std_logic;                                 -- 'Bus is busy' indication (busy = high)

    bus_id      :   out natural range 0 to g_bus_num - 1 := 0;     -- Bus selector

    fsm_state   :   out std_logic_vector(3 downto 0);              -- FSM state

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

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

    mcmd_wr     : in    std_logic;                                 -- Byte command write (active high)

    mcmd_id     : in    std_logic_vector(2 downto 0);              -- Byte command ID

    mcmd_data   : in    std_logic_vector(7 downto 0);              -- Byte command data

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

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

    mrsp_wr     :   out std_logic                    := '0';       -- Byte command response write (active high)

    mrsp_id     :   out std_logic_vector(2 downto 0) := mrsp_done; -- Byte command response control bit

    mrsp_data   :   out std_logic_vector(7 downto 0);              -- Byte command response data

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

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

    mbc_wr      :   out std_logic                    := '0';       -- Bit command write (active high)

    mbc         :   out mbc_type                     := mbc_stop;  -- Bit command

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

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

    mbr_wr      : in    std_logic;                                 -- Bit command response write (active high)

    mbr         : in    mbr_type                                   -- Bit command response

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

  );

end entity mbyte;

--==============================================================================

--==============================================================================

architecture rtl of mbyte is

  constant c_cycle_cnt_inc : integer := 1;

  constant c_cycle_cnt_max : integer := integer(g_f_clk);

  constant c_cycle_cnt_thr : integer := c_cycle_cnt_max - c_cycle_cnt_inc;

  type state_type is

  (

    s_idle,          -- Idle

    s_bus_taken,     -- Bus is taken

    s_start_pending, -- Waiting for right moment to capture bus

    s_start,         -- Sending Start Condition (Capturing the bus)

    s_stop,          -- Sending Stop Condition (Releasing the bus)

    s_write,         -- Sending a byte

    s_read,          -- Receiving a byte

    s_wait           -- Receiving a byte

  );

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

  -- Converting states to std_logic_vector

  function to_std_logic_vector(a : state_type) return std_logic_vector is

  begin

    case (a) is

      when s_idle          => return "0000";

      when s_bus_taken     => return "0001";

      when s_start_pending => return "0010";

      when s_start         => return "0011";

      when s_stop          => return "0100";

      when s_write         => return "0101";

      when s_read          => return "0110";

      when s_wait          => return "0111";

    end case;

  end function to_std_logic_vector;

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

  signal   state           : state_type                         := s_idle;

  signal   cnt             : integer range 0 to 8               := 0;

  signal   sbuf            : std_logic_vector(7 downto 0)       := (others => '0');

  signal   ack             : std_logic                          := '0';

  signal   cycle_cnt       : integer range 0 to c_cycle_cnt_max := 0;

  signal   us_cnt          : unsigned( 7 downto 0)              := to_unsigned(0, 8);

begin

  mrsp_data <= sbuf;

  fsm_state <= to_std_logic_vector(state);

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

  -- Main FSM:

  main_fsm_proc:

  process(clk)

    ---------

    procedure bit_command(a : mbc_type) is

    begin

      mbc_wr <= '1';

      mbc    <= a;

    end procedure bit_command;

    ---------

    ---------

    procedure bit_command(a : std_logic) is

    begin

      mbc_wr <= '1';

      if (a = '0') then

        mbc <= mbc_write_0;

      else

        mbc <= mbc_write_1;

      end if;

    end procedure bit_command;

    ---------

    ---------

    function get_bit(a : mbr_type) return std_logic is

    begin

      if (a = mbr_bit_0) then

        return '0';

      else

        return '1';

      end if;

    end function get_bit;

    ---------

    ---------

    procedure byte_response(a : std_logic_vector(2 downto 0)) is

    begin

      mrsp_wr <= '1';

      mrsp_id <= a;

    end procedure byte_response;

    ---------

    variable v_bus_id   : integer range 0 to 15;

  begin

    if rising_edge(clk) then

      if (s_rst = '1') then

        state     <= s_idle;

        cnt       <= 0;

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

        ack       <= '0';

        mbc_wr    <= '0';

        mbc       <= mbc_stop;

        mrsp_wr   <= '0';

        mrsp_id   <= mrsp_done;

        bus_id    <= 0;

        captured  <= '0';

        cycle_cnt <= 0;

        us_cnt    <= to_unsigned(0, 8);

      else

        -- Default:

        mbc_wr    <= '0';

        mrsp_wr   <= '0';

        ------

        case (state) is

          -- 'Idle' state ----------------------------------

          when s_idle =>

            if (mcmd_wr = '1') then

              case (mcmd_id) is

                when mcmd_start =>

                  -- Begin procedure of bus capturing

                  state     <= s_start_pending;

                when mcmd_set_bus =>

                  -- Switch to another bus

                  state     <= s_idle;

                  v_bus_id  := to_integer(unsigned(mcmd_data(3 downto 0)));

                  if (v_bus_id > (g_bus_num - 1)) then

                    byte_response(mrsp_error);

                  else

                    bus_id    <= v_bus_id;

                    byte_response(mrsp_done);

                  end if;

                when mcmd_wait =>

                  -- Wait for specified period:

                  state     <= s_wait;

                  cycle_cnt <= 0;

                  us_cnt    <= unsigned(mcmd_data);

                when others =>

                  -- Other commands are rejected in 'Idle' state

                  state     <= s_idle;

                  byte_response(mrsp_error);

              end case;

              cnt       <= 0;

            end if;

            captured  <= '0';

          -- 'Idle' state ----------------------------------

          -- 'Wait' state ----------------------------------

          when s_wait =>

            captured  <= '0';

            if (us_cnt = 0) then

              state     <= s_idle;

              byte_response(mrsp_done);

            else

              if (cycle_cnt < c_cycle_cnt_thr) then

                cycle_cnt <= cycle_cnt + c_cycle_cnt_inc;

              else

                cycle_cnt <= cycle_cnt - c_cycle_cnt_thr;

                us_cnt    <= us_cnt - 1;

              end if;

            end if;

          -- 'Wait' state ----------------------------------

          -- 'Bus is Taken' state --------------------------

          when s_bus_taken =>

            if (mcmd_wr = '1') then

              case (mcmd_id) is

                when mcmd_start =>

                  -- Generate Repeated Start condition

                  state     <= s_start;

                  bit_command(mbc_start);

                when mcmd_read_ack =>

                  -- Byte reading with acknowledge

                  state     <= s_read;

                  ack       <= '0';

                  bit_command(mbc_read);

                when mcmd_read_nak =>

                  -- Byte reading with not-acknowledge

                  state     <= s_read;

                  ack       <= '1';

                  bit_command(mbc_read);

                when mcmd_stop =>

                  -- Issue Stop condition

                  state     <= s_stop;

                  bit_command(mbc_stop);

                when mcmd_write =>

                  -- Byte writing

                  state     <= s_write;

                  sbuf      <= mcmd_data(6 downto 0) & '0';

                  bit_command(mcmd_data(7));

                when others =>

                  -- Other commands are rejected in 'Bus Is Taken' state

                  state     <= s_bus_taken;

                  byte_response(mrsp_error);

              end case;

              cnt       <= 0;

            end if;

            captured <= '1';

          -- 'Bus is Taken' state --------------------------

          -- 'Start is Pending' state ----------------------

          when s_start_pending =>

            captured  <= '0';

            if (busy = '0') then

              state     <= s_start;

              bit_command(mbc_start);

            end if;

          -- 'Start is Pending' state ----------------------

          -- 'Start' state ---------------------------------

          when s_start =>

            if (mbr_wr = '1') then

              if (mbr = mbr_done) then

                state     <= s_bus_taken;

                captured  <= '1';

                byte_response(mrsp_done);

              else

                -- (mbr = mbr_arb_lost)

                state     <= s_idle;

                captured  <= '0';

                byte_response(mrsp_arb_lost);

              end if;

            end if;

          -- 'Start' state ---------------------------------

          -- 'Stop' state ----------------------------------

          when s_stop =>

            captured  <= '1';

            if (mbr_wr = '1') then

              state     <= s_idle;

              captured  <= '0';

              byte_response(mrsp_done);

            end if;

          -- 'Stop' state ----------------------------------

          -- 'Byte Reading' state --------------------------

          when s_read =>

            captured  <= '1';

            if (mbr_wr = '1') then

              case (cnt) is

                when 8 =>

                  if (mbr = mbr_done) then

                    -- Return to 'Bus Is Taken' state and

                    -- respond with a byte of data.

                    state     <= s_bus_taken;

                    byte_response(mrsp_byte);

                  else

                    -- (mbr = mbr_arb_lost)

                    state     <= s_idle;

                    captured  <= '0';

                    byte_response(mrsp_arb_lost);

                  end if;

                when others =>

                  if (mbr = mbr_error) then

                    state     <= s_idle;

                    captured  <= '0';

                    byte_response(mrsp_error);

                  else

                    -- (mbr = mbr_bit_0)or(mbr = mbr_bit_1)

                    sbuf      <= sbuf(6 downto 0) & get_bit(mbr);

                    cnt       <= cnt + 1;

                    if (cnt = 7) then

                      -- Write Ack/Nak

                      bit_command(ack);

                    else

                      -- Read a bit

                      bit_command(mbc_read);

                    end if;

                  end if;

              end case;

            end if;

          -- 'Byte Reading' state --------------------------

          -- 'Byte Writing' state --------------------------

          when s_write =>

            captured  <= '1';

            if (mbr_wr = '1') then

              case (cnt) is

                when 8 =>

                  state     <= s_bus_taken;

                  if (mbr = mbr_error) then

                    -- Something went wrong

                    state     <= s_idle;

                    captured  <= '0';

                    byte_response(mrsp_error);

                  elsif (mbr = mbr_bit_0) then

                    -- Write is acknowledged

                    byte_response(mrsp_done);

                  else

                    -- Write is not acknowledged

                    byte_response(mrsp_nak);

                  end if;

                when others =>

                  if (mbr = mbr_done) then

                    sbuf      <= sbuf(6 downto 0) & '0';

                    cnt       <= cnt + 1;

                    if (cnt = 7) then

                      -- Read Ack/Nak

                      bit_command(mbc_read);

                    else

                      -- Write a bit

                      bit_command(sbuf(7));

                    end if;

                  else

                    -- (mbr = mbr_arb_lost)

                    state     <= s_idle;

                    captured  <= '0';

                    byte_response(mrsp_arb_lost);

                  end if;

              end case;

            end if;

          -- 'Byte Writing' state --------------------------

        end case;

      end if;

    end if;

  end process main_fsm_proc;

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

end architecture rtl;

--==============================================================================