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

-- # << NEORV32 - Serial Peripheral Interface Controller (SPI) >>                                  #

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

-- # Frame format: 8/16/24/32-bit receive/transmit data, always MSB first, 2 clock modes,          #

-- # 8 clock speeds (derived from system clock), 8 dedicated chip-select lines (low-active).       #

-- # Interrupt: SPI_transfer_done                                                                  #

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

-- # BSD 3-Clause License                                                                          #

-- #                                                                                               #

-- # Copyright (c) 2020, 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,     #

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

-- # 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_spi 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 --

    spi_sck_o   : out std_ulogic; -- SPI serial clock

    spi_sdo_o   : out std_ulogic; -- controller data out, peripheral data in

    spi_sdi_i   : in  std_ulogic; -- controller data in, peripheral data out

    spi_csn_o   : out std_ulogic_vector(07 downto 0); -- SPI CS

    -- interrupt --

    spi_irq_o   : out std_ulogic -- transmission done interrupt

  );

end neorv32_spi;

architecture neorv32_spi_rtl of neorv32_spi 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(spi_size_c); -- low address boundary bit

  -- control reg bits --

  constant ctrl_spi_cs0_c    : natural :=  0; -- r/w: spi CS 0

  constant ctrl_spi_cs1_c    : natural :=  1; -- r/w: spi CS 1

  constant ctrl_spi_cs2_c    : natural :=  2; -- r/w: spi CS 2

  constant ctrl_spi_cs3_c    : natural :=  3; -- r/w: spi CS 3

  constant ctrl_spi_cs4_c    : natural :=  4; -- r/w: spi CS 4

  constant ctrl_spi_cs5_c    : natural :=  5; -- r/w: spi CS 5

  constant ctrl_spi_cs6_c    : natural :=  6; -- r/w: spi CS 6

  constant ctrl_spi_cs7_c    : natural :=  7; -- r/w: spi CS 7

  --

  constant ctrl_spi_en_c     : natural :=  8; -- r/w: spi enable

  constant ctrl_spi_cpha_c   : natural :=  9; -- r/w: spi clock phase

  constant ctrl_spi_prsc0_c  : natural := 10; -- r/w: spi prescaler select bit 0

  constant ctrl_spi_prsc1_c  : natural := 11; -- r/w: spi prescaler select bit 1

  constant ctrl_spi_prsc2_c  : natural := 12; -- r/w: spi prescaler select bit 2

  constant ctrl_spi_size0_c  : natural := 13; -- r/w: data size (00:  8-bit, 01: 16-bit)

  constant ctrl_spi_size1_c  : natural := 14; -- r/w: data size (10: 24-bit, 11: 32-bit)

  constant ctrl_spi_irq_en_c : natural := 15; -- r/w: spi transmission done interrupt enable

  --

  constant ctrl_spi_busy_c   : natural := 31; -- r/-: spi transceiver is busy

  -- 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

  -- accessible regs --

  signal ctrl        : std_ulogic_vector(15 downto 0);

  signal tx_data_reg : std_ulogic_vector(31 downto 0);

  signal rx_data     : std_ulogic_vector(31 downto 0);

  -- clock generator --

  signal spi_clk : std_ulogic;

  -- spi transceiver --

  signal spi_start      : std_ulogic;

  signal spi_busy       : std_ulogic;

  signal spi_state0     : std_ulogic;

  signal spi_state1     : std_ulogic;

  signal spi_rtx_sreg   : std_ulogic_vector(31 downto 0);

  signal spi_rx_data    : std_ulogic_vector(31 downto 0);

  signal spi_bitcnt     : std_ulogic_vector(05 downto 0);

  signal spi_bitcnt_max : std_ulogic_vector(05 downto 0);

  signal spi_sdi_ff0    : std_ulogic;

  signal spi_sdi_ff1    : std_ulogic;

begin

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

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

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

  addr   <= spi_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 <= acc_en and (rden_i or wren_i);

      -- write access --

      spi_start <= '0';

      if (wren = '1') then

        if (addr = spi_ctrl_addr_c) then -- control

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

        end if;

        if (addr = spi_rtx_addr_c) then -- tx data

          tx_data_reg <= data_i;

          spi_start   <= '1';

        end if;

      end if;

      -- read access --

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

      if (rden = '1') then

        if (addr = spi_ctrl_addr_c) then

          data_o(ctrl_spi_cs0_c)    <= ctrl(ctrl_spi_cs0_c);

          data_o(ctrl_spi_cs1_c)    <= ctrl(ctrl_spi_cs1_c);

          data_o(ctrl_spi_cs2_c)    <= ctrl(ctrl_spi_cs2_c);

          data_o(ctrl_spi_cs3_c)    <= ctrl(ctrl_spi_cs3_c);

          data_o(ctrl_spi_cs4_c)    <= ctrl(ctrl_spi_cs4_c);

          data_o(ctrl_spi_cs5_c)    <= ctrl(ctrl_spi_cs5_c);

          data_o(ctrl_spi_cs6_c)    <= ctrl(ctrl_spi_cs6_c);

          data_o(ctrl_spi_cs7_c)    <= ctrl(ctrl_spi_cs7_c);

          --

          data_o(ctrl_spi_en_c)     <= ctrl(ctrl_spi_en_c);

          data_o(ctrl_spi_cpha_c)   <= ctrl(ctrl_spi_cpha_c);

          data_o(ctrl_spi_prsc0_c)  <= ctrl(ctrl_spi_prsc0_c);

          data_o(ctrl_spi_prsc1_c)  <= ctrl(ctrl_spi_prsc1_c);

          data_o(ctrl_spi_prsc2_c)  <= ctrl(ctrl_spi_prsc2_c);

          data_o(ctrl_spi_size0_c)  <= ctrl(ctrl_spi_size0_c);

          data_o(ctrl_spi_size1_c)  <= ctrl(ctrl_spi_size1_c);

          data_o(ctrl_spi_irq_en_c) <= ctrl(ctrl_spi_irq_en_c);

          --

          data_o(ctrl_spi_busy_c)   <= spi_busy;

        else -- spi_rtx_addr_c

          data_o <= rx_data;

        end if;

      end if;

    end if;

  end process rw_access;

  -- direct chip-select (CS) (output is low-active) --  

  spi_csn_o(7 downto 0) <= not ctrl(ctrl_spi_cs7_c downto ctrl_spi_cs0_c);

  -- Clock Selection ------------------------------------------------------------------------

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

  -- clock generator enable --

  clkgen_en_o <= ctrl(ctrl_spi_en_c);

  -- spi clock select --

  spi_clk <= clkgen_i(to_integer(unsigned(ctrl(ctrl_spi_prsc2_c downto ctrl_spi_prsc0_c))));

  -- SPI Transceiver ------------------------------------------------------------------------

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

  spi_rtx_unit: process(clk_i)

  begin

    if rising_edge(clk_i) then

      -- input (sdi) synchronizer --

      spi_sdi_ff0 <= spi_sdi_i;

      spi_sdi_ff1 <= spi_sdi_ff0;

      -- serial engine --

      spi_irq_o <= '0';

      if (spi_state0 = '0') or (ctrl(ctrl_spi_en_c) = '0') then -- idle or disabled

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

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

        spi_state1 <= '0';

        spi_sdo_o  <= '0';

        spi_sck_o  <= '0';

        if (ctrl(ctrl_spi_en_c) = '0') then -- disabled

          spi_busy <= '0';

        elsif (spi_start = '1') then -- start new transmission

          spi_rtx_sreg <= tx_data_reg;

          spi_busy     <= '1';

        end if;

        spi_state0 <= spi_busy and spi_clk; -- start with next new clock pulse

      else -- transmission in progress

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

        if (spi_state1 = '0') then -- first half of transmission

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

          spi_sck_o <= ctrl(ctrl_spi_cpha_c);

          case ctrl(ctrl_spi_size1_c downto ctrl_spi_size0_c) is

            when "00"   => spi_sdo_o <= spi_rtx_sreg(07); -- 8-bit mode

            when "01"   => spi_sdo_o <= spi_rtx_sreg(15); -- 16-bit mode

            when "10"   => spi_sdo_o <= spi_rtx_sreg(23); -- 24-bit mode

            when others => spi_sdo_o <= spi_rtx_sreg(31); -- 32-bit mode

          end case;

          if (spi_clk = '1') then

            spi_state1 <= '1';

            if (ctrl(ctrl_spi_cpha_c) = '0') then

              spi_rtx_sreg <= spi_rtx_sreg(30 downto 0) & spi_sdi_ff1;

            end if;

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

          end if;

        else -- second half of transmission

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

          spi_sck_o <= not ctrl(ctrl_spi_cpha_c);

          if (spi_clk = '1') then

            spi_state1 <= '0';

            if (ctrl(ctrl_spi_cpha_c) = '1') then

              spi_rtx_sreg <= spi_rtx_sreg(30 downto 0) & spi_sdi_ff1;

            end if;

            if (spi_bitcnt = spi_bitcnt_max) then

              spi_state0 <= '0';

              spi_busy   <= '0';

              spi_irq_o  <= ctrl(ctrl_spi_irq_en_c);

            end if;

          end if;

        end if;

      end if;

    end if;

  end process spi_rtx_unit;

  -- RTX Data size ------------------------------------------------------------------------

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

  data_size: process(ctrl)

  begin

    case ctrl(ctrl_spi_size1_c downto ctrl_spi_size0_c) is

      when "00"   => spi_bitcnt_max <= "001000"; -- 8-bit mode

      when "01"   => spi_bitcnt_max <= "010000"; -- 16-bit mode

      when "10"   => spi_bitcnt_max <= "011000"; -- 24-bit mode

      when others => spi_bitcnt_max <= "100000"; -- 32-bit mode

    end case;

  end process data_size;

  -- RX-Data Masking ------------------------------------------------------------------------

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

  rx_mapping: process(ctrl, spi_rtx_sreg)

  begin

    case ctrl(ctrl_spi_size1_c downto ctrl_spi_size0_c) is

      when "00"   => rx_data <= x"000000" & spi_rtx_sreg(07 downto 0); -- 8-bit mode

      when "01"   => rx_data <= x"0000"   & spi_rtx_sreg(15 downto 0); -- 16-bit mode

      when "10"   => rx_data <= x"00"     & spi_rtx_sreg(23 downto 0); -- 24-bit mode

      when others => rx_data <=             spi_rtx_sreg(31 downto 0); -- 32-bit mode

    end case;

  end process rx_mapping;

end neorv32_spi_rtl;