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
  signal sta_condition : std_logic;       -- start detected
  signal sto_condition : std_logic;       -- stop detected

 detect_sta_sto: process(clk, nRst)
 begin
    if (nRst = '') then
        sta_condition <= '';
        sto_condition <= '';
    elsif (clk'event and clk = '') then
        if (rst = '') then
            sta_condition <= '';
            sto_condition <= '';
        else
            sta_condition <= (not sSDA and dSDA) and sSCL;
            sto_condition <= (sSDA and not dSDA) and sSCL;
        end if;
    end if;
 end process detect_sta_sto;

　　5)　　generate i2c-bus busy signal

 1 -- port
  busy    : out std_logic;      -- i2c bus busy

 4 -- architecture
  signal ibusy  : std_logic;    -- internal busy signal

 gen_busy: process(clk, nRst)
 begin
    if (nRst = '') then
        ibusy <= '';
    elsif (clk'event and clk = '') then
        if (rst = '') then
            ibusy <= '';
        else
            ibusy <= (sta_condition or ibusy) and not sto_condition;
        end if;
    end if;
 end process gen_busy;

 busy <= ibusy;

　　6)　generate arbitration lost signal

 0　-- port
 1　 al　　: out std_logic;  　　-- arbitration lost
 1 -- architecture
  constant I2C_CMD_NOP    : std_logic_vector( downto ) := "";
  constant I2C_CMD_START  : std_logic_vector( downto ) := "";
  constant I2C_CMD_STOP   : std_logic_vector( downto ) := "";
  constant I2C_CMD_READ   : std_logic_vector( downto ) := "";
  constant I2C_CMD_WRITE  : std_logic_vector( downto ) := "";

  signal ial        : std_logic; -- internal arbitration lost signal
  signal sda_chk    : std_logic; -- check SDA status (multi-master arbitration)

11 -- block
   signal cmd_stop    : std_logic;    -- STOP command

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)
 gen_al: process(clk, nRst)
 begin
    if (nRst = '') then
        cmd_stop  <= '';
        ial       <= '';
    elsif (clk'event and clk = '') then
        if (rst = '') then
            cmd_stop  <= '';
            ial       <= '';
        else
            if (clk_en = '') then
                if (cmd = I2C_CMD_STOP) then
                    cmd_stop <= '';
                else
                    cmd_stop <= '';
                end if;
            end if;

            if (c_state = idle) then
                ial <= (sda_chk and not sSDA and isda_oen) or (sto_condition and not cmd_stop);
            else
                ial <= (sda_chk and not sSDA and isda_oen);
            end if;
        end if;
   end if;
 end process gen_al;
 al <= ial;

　　7)　generate dout signal

 1 -- store dout on rising edge of SCL
 gen_dout: process(clk, nReset)
 begin
    if (nReset = '') then
        dout <= '';
    elsif (clk'event and clk = '') then
        if (sSCL = '' and dSCL = '') then
            dout <= sSDA;
        end if;
    end if;
 end process gen_dout;
 end block bus_status_ctrl;