Subversion Repositories udp_ipv4_for_10g_ethernet

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

--

-- (C) Copyright 2017 DFC Design, s.r.o., Brno, Czech Republic

-- Author: Marek Kvas (m.kvas@dfcdesign.cz)

--

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

-- This file is part of UDP/IPv4 for 10 G Ethernet core.

-- 

-- UDP/IPv4 for 10 G Ethernet core is free software: you can 

-- redistribute it and/or modify it under the terms of 

-- the GNU Lesser General Public License as published by the Free 

-- Software Foundation, either version 3 of the License, or

-- (at your option) any later version.

-- 

-- UDP/IPv4 for 10 G Ethernet core is distributed in the hope that 

-- it will be useful, but WITHOUT ANY WARRANTY; without even 

-- the implied warranty of MERCHANTABILITY or FITNESS FOR A 

-- PARTICULAR PURPOSE.  See the GNU Lesser General Public License 

-- for more details.

-- 

-- You should have received a copy of the GNU Lesser General Public 

-- License along with UDP/IPv4 for 10 G Ethernet core.  If not, 

-- see <http://www.gnu.org/licenses/>.

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

--

-- This simple core is used to slow transmission of frames down when

-- link speed is lower than maximum 10 Gbps. AS RXAUI runs on the same

-- frequency regardless of link speed and data are stored in the PHY FIFO

-- it is necessary to insert such IFG that average speed is equal to

-- link speed. Otherwise PHY FIFO overflows and frames get corrupted.

--

-- Output is combinatorial.

--

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

library ieee;

use ieee.std_logic_1164.all;

use ieee.numeric_std.all;

entity frame_throttle is

   port (

      CLK            : in  std_logic;

      LINK_SPEED     : in  std_logic_vector(2 downto 0);

      FG_BUSY        : in  std_logic;

      FG_IDLE_IFG    : in  std_logic;

      BUSY_THROTTLED : out std_logic

        );

end entity;

architecture synthesis of frame_throttle is

   function spd_to_ratio_cnt(spd : std_logic_vector) return natural is

      variable ratio : natural;

   begin

      case to_integer(unsigned(spd)) is

         -- 10 Gbps must be handled differently

         when 1 => ratio := 2; -- 5 Gbps

         when 2 => ratio := 4; -- 2.5 Gbps

         when 3 => ratio := 10; -- 1 Gbps

         when 4 => ratio := 100; -- 100 Mbps

         when others => ratio := 1000; -- 10 Mbps and unsupported link speds

      end case;

      return ratio;

   end function;

   signal busy_throttle_i     : std_logic;

   signal throttle_cnt        : integer range 0 to 2**16-1;

   signal ratio_cnt           : integer range 0 to 1000 -1;

begin

   throttle_proc : process(CLK)

   begin

      if rising_edge(CLK) then

         if LINK_SPEED = "000" then

            -- 10 Gbps - maximal speed

            busy_throttle_i <= '0';

         elsif FG_BUSY = '1' or FG_IDLE_IFG = '1' then

            busy_throttle_i <= '1';

            throttle_cnt <= throttle_cnt + 1;

            ratio_cnt <= 0;

         else

            -- -1 for one cycle spent in cycle counting and

            -- -1 for counter limit as usual forms -2 altogether.

            if ratio_cnt < spd_to_ratio_cnt(LINK_SPEED) - 2 then

               ratio_cnt <= ratio_cnt + 1;

            else

               ratio_cnt <= 0;

               if throttle_cnt > 1 then

                  throttle_cnt <= throttle_cnt - 1;

               else

                  busy_throttle_i <= '0';

               end if;

            end if;

         end if;

      end if;

   end process;

   BUSY_THROTTLED <= FG_BUSY or busy_throttle_i;

end architecture;