source: PlatformSupport/CustomPeripherals/pcores/w3_iic_eeprom_v1_00_b/opencores_src/rtl/vhdl/i2c_master_top.vhd

---------------------------------------------------------------------
----                                                             ----
----  WISHBONE revB2 compl. I2C Master Core; top level           ----
----                                                             ----
----                                                             ----
----  Author: Richard Herveille                                  ----
----          richard@asics.ws                                   ----
----          www.asics.ws                                       ----
----                                                             ----
----  Downloaded from: http://www.opencores.org/projects/i2c/    ----
----                                                             ----
---------------------------------------------------------------------
----                                                             ----
---- Copyright (C) 2000 Richard Herveille                        ----
----                    richard@asics.ws                         ----
----                                                             ----
---- This source file may be used and distributed without        ----
---- restriction provided that this copyright statement is not   ----
---- removed from the file and that any derivative work contains ----
---- the original copyright notice and the associated disclaimer.----
----                                                             ----
----     THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY     ----
---- EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED   ----
---- TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS   ----
---- FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL THE AUTHOR      ----
---- 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.                                 ----
----                                                             ----
---------------------------------------------------------------------

--  CVS Log
--
--  $Id: i2c_master_top.vhd,v 1.8 2009-01-20 10:38:45 rherveille Exp $
--
--  $Date: 2009-01-20 10:38:45 $
--  $Revision: 1.8 $
--  $Author: rherveille $
--  $Locker:  $
--  $State: Exp $
--
-- Change History:
--               Revision 1.7  2004/03/14 10:17:03  rherveille
--               Fixed simulation issue when writing to CR register
--
--               Revision 1.6  2003/08/09 07:01:13  rherveille
--               Fixed a bug in the Arbitration Lost generation caused by delay on the (external) sda line.
--               Fixed a potential bug in the byte controller's host-acknowledge generation.
--
--               Revision 1.5  2003/02/01 02:03:06  rherveille
--               Fixed a few 'arbitration lost' bugs. VHDL version only.
--
--               Revision 1.4  2002/12/26 16:05:47  rherveille
--               Core is now a Multimaster I2C controller.
--
--               Revision 1.3  2002/11/30 22:24:37  rherveille
--               Cleaned up code
--
--               Revision 1.2  2001/11/10 10:52:44  rherveille
--               Changed PRER reset value from 0x0000 to 0xffff, conform specs.
--


library ieee;
use ieee.std_logic_1164.all;

entity i2c_master_top is
    generic(
            ARST_LVL : std_logic := '0'                   -- asynchronous reset level
    );
    port   (
            -- wishbone signals
            wb_clk_i      : in  std_logic;                    -- master clock input
            wb_rst_i      : in  std_logic := '0';             -- synchronous active high reset
            arst_i        : in  std_logic := not ARST_LVL;    -- asynchronous reset
            wb_adr_i      : in  std_logic_vector(2 downto 0); -- lower address bits
            wb_dat_i      : in  std_logic_vector(7 downto 0); -- Databus input
            wb_dat_o      : out std_logic_vector(7 downto 0); -- Databus output
            wb_we_i       : in  std_logic;                    -- Write enable input
            wb_stb_i      : in  std_logic;                    -- Strobe signals / core select signal
            wb_cyc_i      : in  std_logic;                    -- Valid bus cycle input
            wb_ack_o      : out std_logic;                    -- Bus cycle acknowledge output
            wb_inta_o     : out std_logic;                    -- interrupt request output signal

            -- i2c lines
            scl_pad_i     : in  std_logic;                    -- i2c clock line input
            scl_pad_o     : out std_logic;                    -- i2c clock line output
            scl_padoen_o  : out std_logic;                    -- i2c clock line output enable, active low
            sda_pad_i     : in  std_logic;                    -- i2c data line input
            sda_pad_o     : out std_logic;                    -- i2c data line output
            sda_padoen_o  : out std_logic                     -- i2c data line output enable, active low
    );
end entity i2c_master_top;

architecture structural of i2c_master_top is
    component i2c_master_byte_ctrl is
    port (
          clk    : in std_logic;
          rst    : in std_logic; -- synchronous active high reset (WISHBONE compatible)
          nReset : in std_logic; -- asynchornous active low reset (FPGA compatible)
          ena    : in std_logic; -- core enable signal

          clk_cnt : in unsigned(15 downto 0); -- 4x SCL

          -- input signals
          start,
          stop,
          read,
          write,
          ack_in : std_logic;
          din    : in std_logic_vector(7 downto 0);

          -- output signals
          cmd_ack  : out std_logic;
          ack_out  : out std_logic;
          i2c_busy : out std_logic;
          i2c_al   : out std_logic;
          dout     : out std_logic_vector(7 downto 0);

          -- i2c lines
          scl_i   : in std_logic;  -- i2c clock line input
          scl_o   : out std_logic; -- i2c clock line output
          scl_oen : out std_logic; -- i2c clock line output enable, active low
          sda_i   : in std_logic;  -- i2c data line input
          sda_o   : out std_logic; -- i2c data line output
          sda_oen : out std_logic  -- i2c data line output enable, active low
    );
    end component i2c_master_byte_ctrl;

    -- registers
    signal prer : unsigned(15 downto 0);             -- clock prescale register
    signal ctr  : std_logic_vector(7 downto 0);      -- control register
    signal txr  : std_logic_vector(7 downto 0);      -- transmit register
    signal rxr  : std_logic_vector(7 downto 0);      -- receive register
    signal cr   : std_logic_vector(7 downto 0);      -- command register
    signal sr   : std_logic_vector(7 downto 0);      -- status register

    -- internal reset signal
    signal rst_i : std_logic;

    -- wishbone write access
    signal wb_wacc : std_logic;

    -- internal acknowledge signal
    signal iack_o : std_logic;

    -- done signal: command completed, clear command register
    signal done : std_logic;

    -- command register signals
    signal sta, sto, rd, wr, ack, iack : std_logic;

    signal core_en : std_logic;                      -- core enable signal
    signal ien     : std_logic;                      -- interrupt enable signal

    -- status register signals
    signal irxack, rxack : std_logic;                -- received aknowledge from slave
    signal tip           : std_logic;                -- transfer in progress
    signal irq_flag      : std_logic;                -- interrupt pending flag
    signal i2c_busy      : std_logic;                -- i2c bus busy (start signal detected)
    signal i2c_al, al    : std_logic;                -- arbitration lost

begin
    -- generate internal reset signal
    rst_i <= arst_i xor ARST_LVL;

    -- generate acknowledge output signal
    gen_ack_o : process(wb_clk_i)
    begin
        if (wb_clk_i'event and wb_clk_i = '1') then
            iack_o <= wb_cyc_i and wb_stb_i and not iack_o;         -- because timing is always honored
        end if;
    end process gen_ack_o;
    wb_ack_o <= iack_o;

    -- generate wishbone write access signal
    wb_wacc <= wb_we_i and iack_o;

    -- assign wb_dat_o
    assign_dato : process(wb_clk_i)
    begin
        if (wb_clk_i'event and wb_clk_i = '1') then
            case wb_adr_i is
                when "000"  => wb_dat_o <= std_logic_vector(prer( 7 downto 0));
                when "001"  => wb_dat_o <= std_logic_vector(prer(15 downto 8));
                when "010"  => wb_dat_o <= ctr;
                when "011"  => wb_dat_o <= rxr; -- write is transmit register TxR
                when "100"  => wb_dat_o <= sr;  -- write is command register CR

                -- Debugging registers:
                -- These registers are not documented.
                -- Functionality could change in future releases
                when "101"  => wb_dat_o <= txr;
                when "110"  => wb_dat_o <= cr;
                when "111"  => wb_dat_o <= (others => '0');
                when others => wb_dat_o <= (others => 'X'); -- for simulation only
            end case;
        end if;
    end process assign_dato;


    -- generate registers (CR, SR see below)
    gen_regs: process(rst_i, wb_clk_i)
    begin
        if (rst_i = '0') then
            prer <= (others => '1');
            ctr  <= (others => '0');
            txr  <= (others => '0');
        elsif (wb_clk_i'event and wb_clk_i = '1') then
               if (wb_rst_i = '1') then
                   prer <= (others => '1');
                   ctr  <= (others => '0');
                   txr  <= (others => '0');
               elsif (wb_wacc = '1') then
                   case wb_adr_i is
                       when "000" => prer( 7 downto 0) <= unsigned(wb_dat_i);
                       when "001" => prer(15 downto 8) <= unsigned(wb_dat_i);
                       when "010" => ctr               <= wb_dat_i;
                       when "011" => txr               <= wb_dat_i;
                       when "100" => null; --write to CR, avoid executing the others clause

                      -- illegal cases, for simulation only
                      when others =>
                          report ("Illegal write address, setting all registers to unknown.");
                          prer <= (others => 'X');
                          ctr  <= (others => 'X');
                          txr  <= (others => 'X');
                   end case;
               end if;
        end if;
    end process gen_regs;


    -- generate command register
    gen_cr: process(rst_i, wb_clk_i)
    begin
        if (rst_i = '0') then
            cr <= (others => '0');
        elsif (wb_clk_i'event and wb_clk_i = '1') then
            if (wb_rst_i = '1') then
                cr <= (others => '0');
            elsif (wb_wacc = '1') then
                if ( (core_en = '1') and (wb_adr_i = "100") ) then
                    -- only take new commands when i2c core enabled
                    -- pending commands are finished
                    cr <= wb_dat_i;
                end if;
            else
                if (done = '1' or i2c_al = '1') then
                    cr(7 downto 4) <= (others => '0'); -- clear command bits when command done or arbitration lost
                end if;

                cr(2 downto 1) <= (others => '0');   -- reserved bits, always '0'
                cr(0) <= '0';                        -- clear IRQ_ACK bit
            end if;
        end if;
    end process gen_cr;

    -- decode command register
    sta  <= cr(7);
    sto  <= cr(6);
    rd   <= cr(5);
    wr   <= cr(4);
    ack  <= cr(3);
    iack <= cr(0);

    -- decode control register
    core_en <= ctr(7);
    ien     <= ctr(6);

    -- hookup byte controller block
    byte_ctrl: i2c_master_byte_ctrl
    port map (
              clk      => wb_clk_i,
              rst      => wb_rst_i,
              nReset   => rst_i,
              ena      => core_en,
              clk_cnt  => prer,
              start    => sta,
              stop     => sto,
              read     => rd,
              write    => wr,
              ack_in   => ack,
              i2c_busy => i2c_busy,
              i2c_al   => i2c_al,
              din      => txr,
              cmd_ack  => done,
              ack_out  => irxack,
              dout     => rxr,
              scl_i    => scl_pad_i,
              scl_o    => scl_pad_o,
              scl_oen  => scl_padoen_o,
              sda_i    => sda_pad_i,
              sda_o    => sda_pad_o,
              sda_oen  => sda_padoen_o
    );


    -- status register block + interrupt request signal
    st_irq_block : block
    begin
        -- generate status register bits
        gen_sr_bits: process (wb_clk_i, rst_i)
        begin
            if (rst_i = '0') then
                al       <= '0';
                rxack    <= '0';
                tip      <= '0';
                irq_flag <= '0';
            elsif (wb_clk_i'event and wb_clk_i = '1') then
                   if (wb_rst_i = '1') then
                       al       <= '0';
                       rxack    <= '0';
                       tip      <= '0';
                       irq_flag <= '0';
                   else
                       al       <= i2c_al or (al and not sta);
                       rxack    <= irxack;
                       tip      <= (rd or wr);

                       -- interrupt request flag is always generated
                       irq_flag <= (done or i2c_al or irq_flag) and not iack;
                   end if;
            end if;
        end process gen_sr_bits;

        -- generate interrupt request signals
        gen_irq: process (wb_clk_i, rst_i)
        begin
            if (rst_i = '0') then
                wb_inta_o <= '0';
            elsif (wb_clk_i'event and wb_clk_i = '1') then
                   if (wb_rst_i = '1') then
                       wb_inta_o <= '0';
                   else
                       -- interrupt signal is only generated when IEN (interrupt enable bit) is set
                       wb_inta_o <= irq_flag and ien;
                   end if;
            end if;
        end process gen_irq;

        -- assign status register bits
        sr(7)          <= rxack;
        sr(6)          <= i2c_busy;
        sr(5)          <= al;
        sr(4 downto 2) <= (others => '0'); -- reserved
        sr(1)          <= tip;
        sr(0)          <= irq_flag;
    end block;

end architecture structural;