I2C controller core之Bit controller(05)

6　generate statemachine　　

  1 -- port
   cmd_ack : out std_logic;    -- command completed

  4 -- architecture
  type states is (idle, start_a, start_b, start_c, start_d, start_e, stop_a, stop_b,
                  stop_c, stop_d, rd_a, rd_b, rd_c, rd_d, wr_a, wr_b, wr_c, wr_d);
  signal c_state : states;
  signal iscl_oen, isda_oen  : std_logic;   -- internal I2C lines
  signal sda_chk  : std_logic;  -- check SDA status (multi-master arbitration)

 11 -- statemachine
 nxt_state_decoder : process (clk, nRst)
 begin
     if (nRst = '') then
         c_state  <= idle;
         cmd_ack  <= '';
         iscl_oen <= '';
         isda_oen <= '';
         sda_chk  <= '';
     elsif (clk'event and clk = '') then
            if (rst = '' or ial = '') then
                c_state  <= idle;
                cmd_ack  <= '';
                iscl_oen <= '';
                isda_oen <= '';
                sda_chk  <= '';
            else
                cmd_ack <= ''; -- default no acknowledge

                if (clk_en = '') then
                    case (c_state) is
                          -- idle
                          when idle =>
                              case cmd is
                                  when I2C_CMD_START => c_state <= start_a;
                                  when I2C_CMD_STOP  => c_state <= stop_a;
                                  when I2C_CMD_WRITE => c_state <= wr_a;
                                  when I2C_CMD_READ  => c_state <= rd_a;
                                  when others        => c_state <= idle; -- NOP command
                              end case;

                              iscl_oen <= iscl_oen; -- keep SCL in same state
                              isda_oen <= isda_oen; -- keep SDA in same state
                              sda_chk  <= '';      -- don't check SDA

                          -- start
                          when start_a =>
                              c_state  <= start_b;
                              iscl_oen <= iscl_oen; -- keep SCL in same state (for repeated start)
                              isda_oen <= '';      -- set SDA high
                              sda_chk  <= '';      -- don't check SDA

                          when start_b =>
                              c_state  <= start_c;
                              iscl_oen <= ''; -- set SCL high
                              isda_oen <= ''; -- keep SDA high
                              sda_chk  <= ''; -- don't check SDA

                          when start_c =>
                              c_state  <= start_d;
                              iscl_oen <= ''; -- keep SCL high
                              isda_oen <= ''; -- set SDA low
                              sda_chk  <= ''; -- don't check SDA

                          when start_d =>
                              c_state  <= start_e;
                              iscl_oen <= ''; -- keep SCL high
                              isda_oen <= ''; -- keep SDA low
                              sda_chk  <= ''; -- don't check SDA

                          when start_e =>
                              c_state  <= idle;
                              cmd_ack  <= ''; -- command completed
                              iscl_oen <= ''; -- set SCL low
                              isda_oen <= ''; -- keep SDA low
                              sda_chk  <= ''; -- don't check SDA

                          -- stop
                         when stop_a =>
                             c_state  <= stop_b;
                             iscl_oen <= ''; -- keep SCL low
                             isda_oen <= ''; -- set SDA low
                             sda_chk  <= ''; -- don't check SDA

                         when stop_b =>
                             c_state  <= stop_c;
                             iscl_oen <= ''; -- set SCL high
                             isda_oen <= ''; -- keep SDA low
                             sda_chk  <= ''; -- don't check SDA

                         when stop_c =>
                             c_state  <= stop_d;
                             iscl_oen <= ''; -- keep SCL high
                             isda_oen <= ''; -- keep SDA low
                             sda_chk  <= ''; -- don't check SDA

                         when stop_d =>
                             c_state  <= idle;
                             cmd_ack  <= ''; -- command completed
                             iscl_oen <= ''; -- keep SCL high
                             isda_oen <= ''; -- set SDA high
                             sda_chk  <= ''; -- don't check SDA

                         -- read
                         when rd_a =>
                             c_state  <= rd_b;
                             iscl_oen <= ''; -- keep SCL low
                             isda_oen <= ''; -- tri-state SDA
                             sda_chk  <= ''; -- don't check SDA

                         when rd_b =>
                             c_state  <= rd_c;
                             iscl_oen <= ''; -- set SCL high
                             isda_oen <= ''; -- tri-state SDA
                             sda_chk  <= ''; -- don't check SDA

                         when rd_c =>
                             c_state  <= rd_d;
                             iscl_oen <= ''; -- keep SCL high
                             isda_oen <= ''; -- tri-state SDA
                             sda_chk  <= ''; -- don't check SDA

                         when rd_d =>
                             c_state  <= idle;
                             cmd_ack  <= ''; -- command completed
                             iscl_oen <= ''; -- set SCL low
                             isda_oen <= ''; -- tri-state SDA
                             sda_chk  <= ''; -- don't check SDA

                         -- write
                         when wr_a =>
                             c_state  <= wr_b;
                             iscl_oen <= ''; -- keep SCL low
                             isda_oen <= din; -- set SDA
                             sda_chk  <= ''; -- don't check SDA (SCL low)

                         when wr_b =>
                             c_state  <= wr_c;
                             iscl_oen <= ''; -- set SCL high
                             isda_oen <= din; -- keep SDA
                             sda_chk  <= ''; -- don't check SDA yet
                                              -- Allow some more time for SDA and SCL to settle

                         when wr_c =>
                             c_state  <= wr_d;
                             iscl_oen <= ''; -- keep SCL high
                             isda_oen <= din; -- keep SDA
                             sda_chk  <= ''; -- check SDA

                         when wr_d =>
                             c_state  <= idle;
                             cmd_ack  <= ''; -- command completed
                             iscl_oen <= ''; -- set SCL low
                             isda_oen <= din; -- keep SDA
                             sda_chk  <= ''; -- don't check SDA (SCL low)

                         when others =>

                    end case;
                end if;
            end if;
     end if;
 end process nxt_state_decoder;