I2C controller core之Bit controller(04)

　　4)　detect start/stop condition

　　　　START- falling edge on SDA while SCL is high;  STOP -  rising edge on SDA while SCL is high　　

 1 -- block

 2  signal sta_condition : std_logic;       -- start detected

 3  signal sto_condition : std_logic;       -- stop detected

 4 

 5 detect_sta_sto: process(clk, nRst)

 6 begin

 7    if (nRst = '0') then

 8        sta_condition <= '0';

 9        sto_condition <= '0';

10    elsif (clk'event and clk = '1') then

11        if (rst = '1') then

12            sta_condition <= '0';

13            sto_condition <= '0';

14        else

15            sta_condition <= (not sSDA and dSDA) and sSCL;

16            sto_condition <= (sSDA and not dSDA) and sSCL;

17        end if;

18    end if;

19 end process detect_sta_sto;

　　5)　　generate i2c-bus busy signal

 1 -- port

 2  busy    : out std_logic;      -- i2c bus busy

 3 

 4 -- architecture

 5  signal ibusy  : std_logic;    -- internal busy signal

 6 

 7 gen_busy: process(clk, nRst)

 8 begin

 9    if (nRst = '0') then

10        ibusy <= '0';

11    elsif (clk'event and clk = '1') then

12        if (rst = '1') then

13            ibusy <= '0';

14        else

15            ibusy <= (sta_condition or ibusy) and not sto_condition;

16        end if;

17    end if;

18 end process gen_busy;

19 

20 busy <= ibusy;

　　6)　generate arbitration lost signal 

 0　-- port
 1　 al　　: out std_logic;  　　-- arbitration lost
 1 -- architecture

 2  constant I2C_CMD_NOP    : std_logic_vector(3 downto 0) := "0000";

 3  constant I2C_CMD_START  : std_logic_vector(3 downto 0) := "0001";

 4  constant I2C_CMD_STOP   : std_logic_vector(3 downto 0) := "0010";

 5  constant I2C_CMD_READ   : std_logic_vector(3 downto 0) := "0100";

 6  constant I2C_CMD_WRITE  : std_logic_vector(3 downto 0) := "1000";

 7 

 8  signal ial        : std_logic; -- internal arbitration lost signal

 9  signal sda_chk    : std_logic; -- check SDA status (multi-master arbitration)

10 

11 -- block

12   signal cmd_stop    : std_logic;    -- STOP command

13 

14 -- aribitration lost when:

15 -- 1) master drives SDA high, but the i2c bus is low

16 -- 2) stop detected while not requested (detect during 'idle' state)

17 gen_al: process(clk, nRst)

18 begin

19    if (nRst = '0') then

20        cmd_stop  <= '0';

21        ial       <= '0';

22    elsif (clk'event and clk = '1') then

23        if (rst = '1') then

24            cmd_stop  <= '0';

25            ial       <= '0';

26        else

27            if (clk_en = '1') then

28                if (cmd = I2C_CMD_STOP) then

29                    cmd_stop <= '1';

30                else

31                    cmd_stop <= '0';

32                end if;

33            end if;

34 

35            if (c_state = idle) then

36                ial <= (sda_chk and not sSDA and isda_oen) or (sto_condition and not cmd_stop);

37            else

38                ial <= (sda_chk and not sSDA and isda_oen);

39            end if;

40        end if;

41   end if;

42 end process gen_al;

43 al <= ial;

 　　7)　generate dout signal

 1 -- store dout on rising edge of SCL

 2 gen_dout: process(clk, nReset)

 3 begin

 4    if (nReset = '0') then

 5        dout <= '0';

 6    elsif (clk'event and clk = '1') then

 7        if (sSCL = '1' and dSCL = '0') then

 8            dout <= sSDA;

 9        end if;

10    end if;

11 end process gen_dout;

12 end block bus_status_ctrl;