Subversion Repositories neorv32

-- #################################################################################################

-- # << NEORV32 - Two-Wire Interface Controller (TWI) >>                                           #

-- # ********************************************************************************************* #

-- # Supports START and STOP conditions, 8 bit data + ACK/NACK transfers and clock stretching.     #

-- # Supports ACKs by the controller. No multi-controller support and no peripheral mode support   #

-- # yet. Interrupt: "operation done"                                                              #

-- # ********************************************************************************************* #

-- # BSD 3-Clause License                                                                          #

-- #                                                                                               #

-- # Copyright (c) 2021, Stephan Nolting. 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.                                                            #

-- #                                                                                               #

-- # 3. Neither the name of the copyright holder nor the names of its contributors may be used to  #

-- #    endorse or promote products derived from this software without specific prior written      #

-- #    permission.                                                                                #

-- #                                                                                               #

-- # 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 HOLDER 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.                                                            #

-- # ********************************************************************************************* #

-- # The NEORV32 Processor - https://github.com/stnolting/neorv32              (c) Stephan Nolting #

-- #################################################################################################

library ieee;

use ieee.std_logic_1164.all;

use ieee.numeric_std.all;

library neorv32;

use neorv32.neorv32_package.all;

entity neorv32_twi is

  port (

    -- host access --

    clk_i       : in  std_ulogic; -- global clock line

    addr_i      : in  std_ulogic_vector(31 downto 0); -- address

    rden_i      : in  std_ulogic; -- read enable

    wren_i      : in  std_ulogic; -- write enable

    data_i      : in  std_ulogic_vector(31 downto 0); -- data in

    data_o      : out std_ulogic_vector(31 downto 0); -- data out

    ack_o       : out std_ulogic; -- transfer acknowledge

    -- clock generator --

    clkgen_en_o : out std_ulogic; -- enable clock generator

    clkgen_i    : in  std_ulogic_vector(07 downto 0);

    -- com lines --

    twi_sda_io  : inout std_logic; -- serial data line

    twi_scl_io  : inout std_logic; -- serial clock line

    -- interrupt --

    irq_o       : out std_ulogic -- transfer done IRQ

  );

end neorv32_twi;

architecture neorv32_twi_rtl of neorv32_twi is

  -- IO space: module base address --

  constant hi_abb_c : natural := index_size_f(io_size_c)-1; -- high address boundary bit

  constant lo_abb_c : natural := index_size_f(twi_size_c); -- low address boundary bit

  -- control register --

  constant ctrl_en_c    : natural := 0; -- r/w: TWI enable

  constant ctrl_start_c : natural := 1; -- -/w: Generate START condition

  constant ctrl_stop_c  : natural := 2; -- -/w: Generate STOP condition

  constant ctrl_prsc0_c : natural := 3; -- r/w: CLK prsc bit 0

  constant ctrl_prsc1_c : natural := 4; -- r/w: CLK prsc bit 1

  constant ctrl_prsc2_c : natural := 5; -- r/w: CLK prsc bit 2

  constant ctrl_mack_c  : natural := 6; -- r/w: generate ACK by controller for transmission

  --

  constant ctrl_ack_c   : natural := 30; -- r/-: Set if ACK received

  constant ctrl_busy_c  : natural := 31; -- r/-: Set if TWI unit is busy

  --

  signal ctrl : std_ulogic_vector(6 downto 0); -- unit's control register

  -- access control --

  signal acc_en : std_ulogic; -- module access enable

  signal addr   : std_ulogic_vector(31 downto 0); -- access address

  signal wren   : std_ulogic; -- word write enable

  signal rden   : std_ulogic; -- read enable

  -- twi clocking --

  signal twi_clk       : std_ulogic;

  signal twi_phase_gen : std_ulogic_vector(3 downto 0);

  signal twi_clk_phase : std_ulogic_vector(3 downto 0);

  -- twi clock stretching --

  signal twi_clk_halt : std_ulogic;

  -- twi transceiver core --

  signal arbiter  : std_ulogic_vector(2 downto 0);

  signal bitcnt   : std_ulogic_vector(3 downto 0);

  signal rtx_sreg : std_ulogic_vector(8 downto 0); -- main rx/tx shift reg

  -- tri-state I/O --

  signal twi_sda_in_ff : std_ulogic_vector(1 downto 0); -- SDA input sync

  signal twi_scl_in_ff : std_ulogic_vector(1 downto 0); -- SCL input sync

  signal twi_sda_in    : std_ulogic;

  signal twi_scl_in    : std_ulogic;

  signal twi_sda_out   : std_ulogic;

  signal twi_scl_out   : std_ulogic;

begin

  -- Access Control -------------------------------------------------------------------------

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

  acc_en <= '1' when (addr_i(hi_abb_c downto lo_abb_c) = twi_base_c(hi_abb_c downto lo_abb_c)) else '0';

  addr   <= twi_base_c(31 downto lo_abb_c) & addr_i(lo_abb_c-1 downto 2) & "00"; -- word aligned

  wren   <= acc_en and wren_i;

  rden   <= acc_en and rden_i;

  -- Read/Write Access ----------------------------------------------------------------------

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

  rw_access: process(clk_i)

  begin

    if rising_edge(clk_i) then

      ack_o <= rden or wren;

      -- write access --

      if (wren = '1') then

        if (addr = twi_ctrl_addr_c) then

          ctrl <= data_i(ctrl'left downto 0);

        end if;

      end if;

      -- read access --

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

      if (rden = '1') then

        if (addr = twi_ctrl_addr_c) then

          data_o(ctrl_en_c)    <= ctrl(ctrl_en_c);

          data_o(ctrl_prsc0_c) <= ctrl(ctrl_prsc0_c);

          data_o(ctrl_prsc1_c) <= ctrl(ctrl_prsc1_c);

          data_o(ctrl_prsc2_c) <= ctrl(ctrl_prsc2_c);

          data_o(ctrl_mack_c)  <= ctrl(ctrl_mack_c);

          --

          data_o(ctrl_ack_c)   <= not rtx_sreg(0);

          data_o(ctrl_busy_c)  <= arbiter(1) or arbiter(0);

        else -- twi_rtx_addr_c =>

          data_o(7 downto 0)   <= rtx_sreg(8 downto 1);

        end if;

      end if;

    end if;

  end process rw_access;

  -- Clock Generation -----------------------------------------------------------------------

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

  -- clock generator enable --

  clkgen_en_o <= ctrl(ctrl_en_c);

  -- twi clock select --

  twi_clk <= clkgen_i(to_integer(unsigned(ctrl(ctrl_prsc2_c downto ctrl_prsc0_c))));

  -- generate four non-overlapping clock ticks at twi_clk/4 --

  clock_phase_gen: process(clk_i)

  begin

    if rising_edge(clk_i) then

      if (arbiter(2) = '0') or (arbiter(1 downto 0) = "00") then -- offline or idle

        twi_phase_gen <= "0001"; -- make sure to start with a new phase, bit 0,1,2,3 stepping

      elsif (twi_clk = '1') and (twi_clk_halt = '0') then -- enabled and no clock stretching detected

        twi_phase_gen <= twi_phase_gen(2 downto 0) & twi_phase_gen(3); -- rotate left

      end if;

    end if;

  end process clock_phase_gen;

  -- TWI bus signals are set/sampled using 4 clock phases --

  twi_clk_phase(0) <= twi_phase_gen(0) and twi_clk; -- first step

  twi_clk_phase(1) <= twi_phase_gen(1) and twi_clk;

  twi_clk_phase(2) <= twi_phase_gen(2) and twi_clk;

  twi_clk_phase(3) <= twi_phase_gen(3) and twi_clk; -- last step

  -- TWI Transceiver ------------------------------------------------------------------------

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

  twi_rtx_unit: process(clk_i)

  begin

    if rising_edge(clk_i) then

      -- input synchronizer & sampler --

      twi_sda_in_ff <= twi_sda_in_ff(0) & twi_sda_in;

      twi_scl_in_ff <= twi_scl_in_ff(0) & twi_scl_in;

      -- defaults --

      irq_o <= '0';

      -- serial engine --

      arbiter(2) <= ctrl(ctrl_en_c); -- still activated?

      case arbiter is

        when "100" => -- IDLE: waiting for requests, bus might be still claimed by this controller if no STOP condition was generated

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

          if (wren = '1') then

            if (addr = twi_ctrl_addr_c) then

              if (data_i(ctrl_start_c) = '1') then -- issue START condition

                arbiter(1 downto 0) <= "01";

              elsif (data_i(ctrl_stop_c) = '1') then  -- issue STOP condition

                arbiter(1 downto 0) <= "10";

              end if;

            elsif (addr = twi_rtx_addr_c) then -- start a data transmission

              -- one bit extra for ack, issued by controller if ctrl_mack_c is set,

              -- sampled from peripheral if ctrl_mack_c is cleared

              rtx_sreg <= data_i(7 downto 0) & (not ctrl(ctrl_mack_c));

              arbiter(1 downto 0) <= "11";

            end if;

          end if;

        when "101" => -- START: generate START condition

          if (twi_clk_phase(0) = '1') then

            twi_sda_out <= '1';

          elsif (twi_clk_phase(1) = '1') then

            twi_sda_out <= '0';

          end if;

          --

          if (twi_clk_phase(0) = '1') then

            twi_scl_out <= '1';

          elsif (twi_clk_phase(3) = '1') then

            twi_scl_out <= '0';

            irq_o       <= '1'; -- Interrupt!

            arbiter(1 downto 0) <= "00"; -- go back to IDLE

          end if;

        when "110" => -- STOP: generate STOP condition

          if (twi_clk_phase(0) = '1') then

            twi_sda_out <= '0';

          elsif (twi_clk_phase(3) = '1') then

            twi_sda_out <= '1';

            irq_o       <= '1'; -- Interrupt!

            arbiter(1 downto 0) <= "00"; -- go back to IDLE

          end if;

          --

          if (twi_clk_phase(0) = '1') then

            twi_scl_out <= '0';

          elsif (twi_clk_phase(1) = '1') then

            twi_scl_out <= '1';

          end if;

        when "111" => -- TRANSMISSION: transmission in progress

          if (twi_clk_phase(0) = '1') then

            bitcnt    <= std_ulogic_vector(unsigned(bitcnt) + 1);

            twi_scl_out <= '0';

            twi_sda_out <= rtx_sreg(8); -- MSB first

          elsif (twi_clk_phase(1) = '1') then -- first half + second half of valid data strobe

            twi_scl_out <= '1';

          elsif (twi_clk_phase(3) = '1') then

            rtx_sreg  <= rtx_sreg(7 downto 0) & twi_sda_in_ff(twi_sda_in_ff'left); -- sample and shift left

            twi_scl_out <= '0';

          end if;

          --

          if (bitcnt = "1010") then -- 8 data bits + 1 bit for ACK + 1 tick delay

            irq_o <= '1'; -- Interrupt!

            arbiter(1 downto 0) <= "00"; -- go back to IDLE

          end if;

        when others => -- "0--" OFFLINE: TWI deactivated

          twi_sda_out <= '1';

          twi_scl_out <= '1';

          arbiter(1 downto 0) <= "00"; -- stay here, go to idle when activated

      end case;

    end if;

  end process twi_rtx_unit;

  -- Clock Stretching Detector --------------------------------------------------------------

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

  -- controller wants to pull SCL high, but SCL is pulled low by peripheral --

  twi_clk_halt <= '1' when (twi_scl_out = '1') and (twi_scl_in_ff(twi_scl_in_ff'left) = '0') else '0';

  -- Tri-State Driver -----------------------------------------------------------------------

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

  -- SDA and SCL need to be of type std_logic to be correctly resolved in simulation

  twi_sda_io <= '0' when (twi_sda_out = '0') else 'Z';

  twi_scl_io <= '0' when (twi_scl_out = '0') else 'Z';

  -- read-back --

  twi_sda_in <= std_ulogic(twi_sda_io);

  twi_scl_in <= std_ulogic(twi_scl_io);

end neorv32_twi_rtl;