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[/] [mod_sim_exp/] [trunk/] [rtl/] [vhdl/] [core/] [pulse_cdc.vhd] - Rev 94
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---------------------------------------------------------------------- ---- pulse_cdc ---- ---- ---- ---- This file is part of the ---- ---- Modular Simultaneous Exponentiation Core project ---- ---- http://www.opencores.org/cores/mod_sim_exp/ ---- ---- ---- ---- Description ---- ---- transfers a pulse (1clk wide) from clock domain A to ---- ---- clock domain B by using a toggling signal. This design ---- ---- avoids metastable states ---- ---- ---- ---- Dependencies: none ---- ---- ---- ---- Authors: ---- ---- - Geoffrey Ottoy, DraMCo research group ---- ---- - Jonas De Craene, JonasDC@opencores.org ---- ---- ---- ---------------------------------------------------------------------- ---- ---- ---- Copyright (C) 2011 DraMCo research group and OPENCORES.ORG ---- ---- ---- ---- This source file may be used and distributed without ---- ---- restriction provided that this copyright statement is not ---- ---- removed from the file and that any derivative work contains ---- ---- the original copyright notice and the associated disclaimer. ---- ---- ---- ---- This source file 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 2.1 of the License, or (at your option) any ---- ---- later version. ---- ---- ---- ---- This source 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 this source; if not, download it ---- ---- from http://www.opencores.org/lgpl.shtml ---- ---- ---- ---------------------------------------------------------------------- library ieee; use ieee.std_logic_1164.all; use ieee.std_logic_unsigned.all; entity pulse_cdc is port ( reset : in std_logic; clkA : in std_logic; pulseA : in std_logic; clkB : in std_logic; pulseB : out std_logic ); end pulse_cdc; architecture arch of pulse_cdc is signal pulseA_d : std_logic; signal toggle : std_logic := '0'; signal toggle_d, toggle_d2, toggle_d3 : std_logic; begin -- Convert pulse from clock domain A to a toggling signal PulseAtoToggle : process (clkA, reset) begin if reset='1' then toggle <= '0'; else if rising_edge(clkA) then pulseA_d <= pulseA; toggle <= toggle xor (pulseA and not pulseA_d); end if; end if; end process; -- Convert toggling signal to a pulse of 1clk wide to clock domain B ToggletoPulseB : process (clkB, reset) begin if reset='1' then toggle_d <= '0'; toggle_d2 <= '0'; toggle_d3 <= '0'; else if rising_edge(clkB) then toggle_d <= toggle; -- this signal may have metastability isues toggle_d2 <= toggle_d; -- stable now toggle_d3 <= toggle_d2; end if; end if; end process; pulseB <= toggle_d2 xor toggle_d3; end arch;