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[/] [astron_fifo/] [trunk/] [common_rl_decrease.vhd] - Rev 2
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------------------------------------------------------------------------------- -- -- Copyright (C) 2013 -- ASTRON (Netherlands Institute for Radio Astronomy) <http://www.astron.nl/> -- JIVE (Joint Institute for VLBI in Europe) <http://www.jive.nl/> -- P.O.Box 2, 7990 AA Dwingeloo, The Netherlands -- -- This program is free software: you can redistribute it and/or modify -- it under the terms of the GNU General Public License as published by -- the Free Software Foundation, either version 3 of the License, or -- (at your option) any later version. -- -- This program 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 General Public License for more details. -- -- You should have received a copy of the GNU General Public License -- along with this program. If not, see <http://www.gnu.org/licenses/>. -- ------------------------------------------------------------------------------- -- >>> Ported from UniBoard dp_latency_adapter for fixed RL 0 --> 1 LIBRARY IEEE; USE IEEE.std_logic_1164.ALL; -- Purpose: Adapt from ready latency 1 to 0 to make a look ahead FIFO -- Description: - -- Remark: -- . A show ahead FIFO with RL=0 does not need a rd_emp output signal, because -- with RL=0 the rd_val='0' when it is empty (so emp <= NOT rd_val). ENTITY common_rl_decrease IS GENERIC ( g_adapt : BOOLEAN := TRUE; -- default when TRUE then decrease sink RL 1 to source RL 0, else then implement wires g_dat_w : NATURAL := 18 ); PORT ( rst : IN STD_LOGIC; clk : IN STD_LOGIC; -- ST sink: RL = 1 snk_out_ready : OUT STD_LOGIC; snk_in_dat : IN STD_LOGIC_VECTOR(g_dat_w-1 DOWNTO 0); snk_in_val : IN STD_LOGIC := 'X'; -- ST source: RL = 0 src_in_ready : IN STD_LOGIC; src_out_dat : OUT STD_LOGIC_VECTOR(g_dat_w-1 DOWNTO 0); src_out_val : OUT STD_LOGIC ); END common_rl_decrease; ARCHITECTURE rtl OF common_rl_decrease IS -- Internally use streaming record for the SOSI, for the SISO.ready directly use src_in_ready TYPE t_sosi IS RECORD -- Source Out or Sink In data : STD_LOGIC_VECTOR(g_dat_w-1 DOWNTO 0); valid : STD_LOGIC; END RECORD; TYPE t_sosi_arr IS ARRAY (INTEGER RANGE <>) OF t_sosi; CONSTANT c_sosi_rst : t_sosi := ((OTHERS=>'0'), '0'); -- SOSI IO SIGNAL snk_in : t_sosi; SIGNAL src_out : t_sosi; -- The default FIFO has ready latency RL = 1, need to use input RL + 1 words for the buf array, to go to output RL = 0 for show ahead FIFO SIGNAL buf : t_sosi_arr(1 DOWNTO 0); SIGNAL nxt_buf : t_sosi_arr(1 DOWNTO 0); BEGIN gen_wires : IF g_adapt=FALSE GENERATE snk_out_ready <= src_in_ready; src_out_dat <= snk_in_dat; src_out_val <= snk_in_val; END GENERATE; gen_adapt : IF g_adapt=TRUE GENERATE snk_in.data <= snk_in_dat; snk_in.valid <= snk_in_val; src_out_dat <= src_out.data; src_out_val <= src_out.valid; -- Buf[0] contains the FIFO output with zero ready latency src_out <= buf(0); p_clk : PROCESS(rst, clk) BEGIN IF rst='1' THEN buf <= (OTHERS=>c_sosi_rst); ELSIF rising_edge(clk) THEN buf <= nxt_buf; END IF; END PROCESS; p_snk_out_ready : PROCESS(buf, src_in_ready, snk_in) BEGIN snk_out_ready <= '0'; IF src_in_ready='1' THEN -- Default snk_out_ready when src_in_ready. snk_out_ready <= '1'; ELSE -- Extra snk_out_ready to look ahead for RL = 0. IF buf(0).valid='0' THEN snk_out_ready <= '1'; ELSIF buf(1).valid='0' THEN snk_out_ready <= NOT(snk_in.valid); END IF; END IF; END PROCESS; p_buf : PROCESS(buf, src_in_ready, snk_in) BEGIN -- Keep or shift the buf dependent on src_in_ready, no need to explicitly check buf().valid nxt_buf <= buf; IF src_in_ready='1' THEN nxt_buf(0) <= buf(1); nxt_buf(1).valid <= '0'; -- not strictly necessary, but robust END IF; -- Put input data at the first available location dependent on src_in_ready, no need to explicitly check snk_in_val IF buf(0).valid='0' THEN nxt_buf(0) <= snk_in; ELSE IF buf(1).valid='0' THEN IF src_in_ready='0' THEN nxt_buf(1) <= snk_in; ELSE nxt_buf(0) <= snk_in; END IF; END IF; END IF; END PROCESS; END GENERATE; END rtl;
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