Subversion Repositories neorv32

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

-- # << NEORV32 - Machine System Timer (MTIME) >>                                                  #

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

-- # Compatible to RISC-V spec's mtime & mtimecmp.                                                 #

-- # Write mtime.LO first when updating the system time. System time should be written only at     #

-- # system start. RISC-V spec. exception: The MTIME interrupt is ACKed by the processor itself.   #

-- # However, the  achine time cannot issue a new interrupt until the mtimecmp.HI register is      #

-- # written again.                                                                                #

-- # Note: The 64-bit time and compare system is broken and de-coupled into two 32-bit systems.    #

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

-- # 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,     #

-- # 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_mtime is

  port (

    -- host access --

    clk_i     : in  std_ulogic; -- global clock line

    rstn_i    : in  std_ulogic := '0'; -- global reset, low-active, async

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

    rden_i    : in  std_ulogic; -- read enable

    wren_i    : in  std_ulogic; -- write enable

    ben_i     : in  std_ulogic_vector(03 downto 0); -- byte 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

    -- interrupt --

    irq_o     : out std_ulogic  -- interrupt request

  );

end neorv32_mtime;

architecture neorv32_mtime_rtl of neorv32_mtime 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(mtime_size_c); -- low address boundary bit

  -- access control --

  signal acc_en : std_ulogic; -- module access enable

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

  signal wren   : std_ulogic; -- module access enable

  -- accessible regs --

  signal mtimecmp        : std_ulogic_vector(63 downto 0);

  signal mtime_lo        : std_ulogic_vector(32 downto 0);

  signal mtime_lo_msb_ff : std_ulogic;

  signal mtime_hi        : std_ulogic_vector(31 downto 0);

  -- irq control --

  signal cmp_lo       : std_ulogic;

  signal cmp_lo_ff    : std_ulogic;

  signal cmp_hi       : std_ulogic;

  signal cmp_match_ff : std_ulogic;

  signal irq_flag     : std_ulogic;

  signal irq_flag_ff  : std_ulogic;

begin

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

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

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

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

  wren   <= acc_en and wren_i;

  -- System Time Update ---------------------------------------------------------------------

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

  system_time: process(clk_i)

  begin

    if rising_edge(clk_i) then

      if (rstn_i = '0') then

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

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

      else

        -- mtime low --

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

        -- mtime high --

        if ((mtime_lo_msb_ff xor mtime_lo(mtime_lo'left)) = '1') then -- mtime_lo carry?

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

        end if;

      end if;

    end if;

  end process system_time;

  -- Write Access ---------------------------------------------------------------------------

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

  wr_access: process(clk_i)

  begin

    if rising_edge(clk_i) then

      ack_o <= acc_en and (rden_i or wren_i);

      -- mtimecmp low --

      if (wren = '1') and (addr = mtime_cmp_lo_addr_c) then

        for i in 0 to 3 loop

          if (ben_i(i) = '1') then

            mtimecmp(00+7+i*8 downto 00+0+i*8) <= data_i(7+i*8 downto 0+i*8);

          end if;

        end loop; -- byte enable

      end if;

      -- mtimecmp high --

      if (wren = '1') and (addr = mtime_cmp_hi_addr_c) then

        for i in 0 to 3 loop

          if (ben_i(i) = '1') then

            mtimecmp(32+7+i*8 downto 32+0+i*8) <= data_i(7+i*8 downto 0+i*8);

          end if;

        end loop; -- byte enable

      end if;

    end if;

  end process wr_access;

  -- Read Access ----------------------------------------------------------------------------

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

  rd_access: process(clk_i)

  begin

    if rising_edge(clk_i) then

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

      if (rden_i = '1') and (acc_en = '1') then

        if (addr = mtime_time_lo_addr_c) then -- mtime LOW

          data_o <= mtime_lo(31 downto 00);

        elsif (addr = mtime_time_hi_addr_c) then -- mtime HIGH

          data_o <= mtime_hi;

        elsif (addr = mtime_cmp_lo_addr_c) then -- mtimecmp LOW

          data_o <= mtimecmp(31 downto 00);

        else -- (addr = mtime_cmp_hi_addr_c) then -- mtimecmp HIGH

          data_o <= mtimecmp(63 downto 32);

        end if;

      end if;

    end if;

  end process rd_access;

  -- Comparator -----------------------------------------------------------------------------

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

  cmp_sync: process(clk_i)

  begin

    if rising_edge(clk_i) then

      cmp_lo_ff    <= cmp_lo;

      cmp_match_ff <= cmp_lo_ff and cmp_hi;

    end if;

  end process cmp_sync;

  -- test words --

  cmp_lo <= '1' when (unsigned(mtime_lo(31 downto 00)) >= unsigned(mtimecmp(31 downto 00))) else '0';

  cmp_hi <= '1' when (unsigned(mtime_hi(31 downto 00)) >= unsigned(mtimecmp(63 downto 32))) else '0';

  -- Interrupt Logic ------------------------------------------------------------------------

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

  irq_ctrl: process(clk_i)

  begin

    if rising_edge(clk_i) then

      if (rstn_i = '0') then

        irq_flag_ff <= '0';

        irq_flag    <= '0';

      else

        irq_flag_ff  <= irq_flag;

        if (irq_flag = '0') then -- idle

          irq_flag <= '0';

          if (cmp_match_ff = '1') then

            irq_flag <= '1';

          end if;

        elsif (wren = '1') and (addr = mtime_cmp_hi_addr_c) then -- ACK

          irq_flag <= '0';

        end if;

      end if;

    end if;

  end process irq_ctrl;

  -- irq output to CPU --

  irq_o <= irq_flag and (not irq_flag_ff); -- rising edge detector

end neorv32_mtime_rtl;