Subversion Repositories astron_mm

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

--

-- Copyright 2020

-- ASTRON (Netherlands Institute for Radio Astronomy) <http://www.astron.nl/>

-- P.O.Box 2, 7990 AA Dwingeloo, The Netherlands

-- 

-- Licensed under the Apache License, Version 2.0 (the "License");

-- you may not use this file except in compliance with the License.

-- You may obtain a copy of the License at

-- 

--     http://www.apache.org/licenses/LICENSE-2.0

-- 

-- Unless required by applicable law or agreed to in writing, software

-- distributed under the License is distributed on an "AS IS" BASIS,

-- WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

-- See the License for the specific language governing permissions and

-- limitations under the License.

--

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

LIBRARY IEEE, common_pkg_lib, common_components_lib, astron_ram_lib;

USE IEEE.std_logic_1164.ALL;

USE IEEE.numeric_std.ALL;

USE common_pkg_lib.common_pkg.ALL;

USE astron_ram_lib.common_ram_pkg.ALL;

-- Purpose: Get in_dat from in_clk to out_clk domain when in_new is asserted.

-- Remarks:

-- . If in_new is a pulse, then new in_dat is available after g_in_new_latency.

-- . It is also allowed to hold in_new high, then out_new will pulse once for

--   every 24 out_clk cycles.

-- . Use in_done to be sure that in_dat due to in_new has crossed the clock

--   domain, in case of multiple in_new pulses in a row the in_done will only

--   pulse when this state remains s_idle, so after the last in_new.

-- . If the in_dat remains unchanged during the crossing of in_new to out_en

--   then g_input_buf=FALSE may be used to save some flipflops

ENTITY common_reg_cross_domain IS

  GENERIC (

    g_input_buf      : BOOLEAN := TRUE;

    g_in_new_latency : NATURAL := 0;  -- >= 0

    g_out_dat_init   : STD_LOGIC_VECTOR(c_mem_reg_init_w-1 DOWNTO 0) := (OTHERS => '0')

  );

  PORT (

    in_rst      : IN  STD_LOGIC;

    in_clk      : IN  STD_LOGIC;

    in_new      : IN  STD_LOGIC := '1';  -- when '1' then new in_dat is available after g_in_new_latency

    in_dat      : IN  STD_LOGIC_VECTOR;

    in_done     : OUT STD_LOGIC;         -- pulses when no more pending in_new

    out_rst     : IN  STD_LOGIC;

    out_clk     : IN  STD_LOGIC;

    out_dat     : OUT STD_LOGIC_VECTOR;

    out_new     : OUT STD_LOGIC          -- when '1' then the out_dat was updated with in_dat due to in_new

  );

END common_reg_cross_domain;

ARCHITECTURE rtl OF common_reg_cross_domain IS

  CONSTANT c_dat : STD_LOGIC_VECTOR(in_dat'RANGE) := g_out_dat_init(in_dat'RANGE);

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

  -- in_clk domain

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

  SIGNAL reg_new          : STD_LOGIC_VECTOR(0 TO g_in_new_latency) := (OTHERS=>'0');

  SIGNAL nxt_reg_new      : STD_LOGIC_VECTOR(reg_new'RANGE);

  SIGNAL in_buf           : STD_LOGIC_VECTOR(c_dat'RANGE) := c_dat;

  SIGNAL in_buf_reg       : STD_LOGIC_VECTOR(c_dat'RANGE) := c_dat;

  SIGNAL nxt_in_buf_reg   : STD_LOGIC_VECTOR(c_dat'RANGE);

  -- Register access clock domain crossing

  TYPE t_state_enum IS (s_idle, s_busy);

  SIGNAL cross_req        : STD_LOGIC;

  SIGNAL cross_busy       : STD_LOGIC;

  SIGNAL nxt_in_done      : STD_LOGIC;

  SIGNAL state            : t_state_enum;

  SIGNAL nxt_state        : t_state_enum;

  SIGNAL prev_state       : t_state_enum;

  SIGNAL in_new_hold      : STD_LOGIC;

  SIGNAL nxt_in_new_hold  : STD_LOGIC;

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

  -- out_clk domain

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

  SIGNAL out_en           : STD_LOGIC;

  SIGNAL i_out_dat        : STD_LOGIC_VECTOR(c_dat'RANGE) := c_dat;  -- register init without physical reset

  SIGNAL nxt_out_dat      : STD_LOGIC_VECTOR(c_dat'RANGE);

BEGIN

  out_dat <= i_out_dat;

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

  -- in_clk domain

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

  reg_new(0) <= in_new;

  gen_latency : IF g_in_new_latency>0 GENERATE

    p_reg_new : PROCESS(in_rst, in_clk)

    BEGIN

      IF in_rst='1' THEN

        reg_new(1 TO g_in_new_latency) <= (OTHERS=>'0');

      ELSIF rising_edge(in_clk) THEN

        reg_new(1 TO g_in_new_latency) <= nxt_reg_new(1 TO g_in_new_latency);

      END IF;

    END PROCESS;

    nxt_reg_new(1 TO g_in_new_latency) <= reg_new(0 TO g_in_new_latency-1);

  END GENERATE;

  p_in_clk : PROCESS(in_rst, in_clk)

  BEGIN

    IF in_rst='1' THEN

      in_new_hold <= '0';

      in_done     <= '0';

      state       <= s_idle;

      prev_state  <= s_idle;

    ELSIF rising_edge(in_clk) THEN

      in_buf_reg  <= nxt_in_buf_reg;

      in_new_hold <= nxt_in_new_hold;

      in_done     <= nxt_in_done;

      state       <= nxt_state;

      prev_state  <= state;

    END IF;

  END PROCESS;

  -- capture the new register data

  no_in_buf : IF g_input_buf=FALSE GENERATE

    in_buf <= in_dat;  -- assumes that in_dat remains unchanged during the crossing of in_new to out_en

  END GENERATE;

  gen_in_buf : IF g_input_buf=TRUE GENERATE

    nxt_in_buf_reg <= in_dat WHEN cross_req='1' ELSE in_buf_reg;

    in_buf         <= in_buf_reg;

  END GENERATE;

  -- handshake control of the clock domain crossing by u_cross_req

  -- hold any subsequent in_new during cross domain busy to ensure that the out_dat will get the latest value of in_dat

  p_state : PROCESS(state, prev_state, reg_new, in_new_hold, cross_busy)

  BEGIN

    cross_req <= '0';

    nxt_in_done <= '0';

    nxt_in_new_hold <= in_new_hold;

    nxt_state <= state;

    CASE state IS

      WHEN s_idle =>

        nxt_in_new_hold <= '0';

        IF reg_new(g_in_new_latency)='1' OR in_new_hold='1' THEN

          cross_req <= '1';

          nxt_state <= s_busy;

        ELSIF UNSIGNED(reg_new)=0 AND prev_state=s_busy THEN

          nxt_in_done <= '1';  -- no pending in_new at input or in shift register and just left s_busy, so signal in_done

        END IF;

      WHEN OTHERS => -- s_busy

        IF reg_new(g_in_new_latency)='1' THEN

          nxt_in_new_hold <= '1';

        END IF;

        IF cross_busy='0' THEN

          nxt_state <= s_idle;

        END IF;

    END CASE;

  END PROCESS;

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

  -- cross clock domain

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

  u_cross_req : ENTITY common_components_lib.common_spulse

  PORT MAP (

    in_rst     => in_rst,

    in_clk     => in_clk,

    in_pulse   => cross_req,

    in_busy    => cross_busy,

    out_rst    => out_rst,

    out_clk    => out_clk,

    out_pulse  => out_en

  );

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

  -- out_clk domain

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

  p_out_clk : PROCESS(out_rst, out_clk)

  BEGIN

    IF out_rst='1' THEN

      out_new   <= '0';

    ELSIF rising_edge(out_clk) THEN

      i_out_dat <= nxt_out_dat;

      out_new   <= out_en;

    END IF;

  END PROCESS;

  -- some clock cycles after the cross_req the in_buf data is stable for sure

  nxt_out_dat <= in_buf WHEN out_en='1' ELSE i_out_dat;

END rtl;