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-------------------------------------------------------------------------------
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--
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-- Copyright (C) 2010
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-- ASTRON (Netherlands Institute for Radio Astronomy) <http://www.astron.nl/>
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-- JIVE (Joint Institute for VLBI in Europe) <http://www.jive.nl/>
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-- P.O.Box 2, 7990 AA Dwingeloo, The Netherlands
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--
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-- This program is free software: you can redistribute it and/or modify
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-- it under the terms of the GNU General Public License as published by
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-- the Free Software Foundation, either version 3 of the License, or
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-- (at your option) any later version.
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--
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-- This program is distributed in the hope that it will be useful,
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-- but WITHOUT ANY WARRANTY; without even the implied warranty of
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-- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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-- GNU General Public License for more details.
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--
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-- You should have received a copy of the GNU General Public License
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-- along with this program. If not, see <http://www.gnu.org/licenses/>.
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--
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-------------------------------------------------------------------------------
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LIBRARY IEEE, dp_pkg_lib;
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USE IEEE.std_logic_1164.all;
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USE dp_pkg_lib.dp_stream_pkg.ALL;
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-- Purpose:
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-- Hold the sink input
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-- Description:
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-- This dp_hold_input provides the necessary input logic to hold the input
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-- data and control to easily register the source output. Compared to
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-- dp_pipeling the dp_hold_input is the same except for the output register
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-- stage. In this way dp_hold_input can be used in a more complicated stream
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-- component where the output is not always the same as the input.
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-- The snk_in.valid and hold_in.valid are never high at the same time.
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-- If src_in.ready goes low while snk_in.valid is high then this snk_in.valid
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-- is held in hold_in.valid and the corresponding snk_in.data will get held
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-- in the external src_out_reg.data. When src_in.ready goes high again then
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-- the held data becomes valid via src_out_reg.valid and hold_in.valid goes
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-- low. Due to the RL=1 the next cycle the snk_in.valid from the sink may go
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-- high. The next_src_out control signals are equal to pend_src_out AND
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-- src_in.ready, so they can directly be assigned to src_out_reg.data if the
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-- snk_in.data needs to be passed on.
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-- The internal pend_src_out control signals are available outside, in
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-- addition to the next_src_out control signals, to support external control
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-- independent of src_in.ready. Use pend_scr_out instead of next_src_out
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-- to avoid combinatorial loop when src_in.ready depends on next_src_out.
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-- The pend_src_out signals are used to implement show ahead behaviour like
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-- with RL=0, but for RL=1. The input can then be stopped based on the snk_in
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-- data and later on continued again without losing this snk_in data, because
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-- it was held as described above.
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-- Remarks:
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-- . Ready latency = 1
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-- . Without flow control so when src_in.ready = '1' fixed, then dp_hold_input
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-- becomes void because the dp_hold_ctrl output then remains '0'.
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ENTITY dp_hold_input IS
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PORT (
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rst : IN STD_LOGIC;
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clk : IN STD_LOGIC;
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-- ST sink
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snk_out : OUT t_dp_siso;
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snk_in : IN t_dp_sosi;
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-- ST source
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src_in : IN t_dp_siso;
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next_src_out : OUT t_dp_sosi;
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pend_src_out : OUT t_dp_sosi; -- the SOSI data fields are the same as for next_src_out
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src_out_reg : IN t_dp_sosi -- uses only the SOSI data fields
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);
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END dp_hold_input;
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ARCHITECTURE rtl OF dp_hold_input IS
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SIGNAL i_pend_src_out : t_dp_sosi;
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SIGNAL hold_in : t_dp_sosi; -- uses only the SOSI ctrl fields
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BEGIN
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pend_src_out <= i_pend_src_out;
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-- SISO:
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snk_out <= src_in; -- No change in ready latency, pass on xon frame level flow control
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-- SOSI:
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-- Take care of active snk_in.valid, snk_in.sync, snk_in.sop and snk_in.eop
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-- when src_in.ready went low. If hold_in.valid would not be used for
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-- pend_src_out.valid and next_src_out.valid, then the pipeline would still
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-- work, but the valid snk_in.data that came when src_in.ready went low,
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-- will then only get pushed out on the next valid snk_in.valid. Whereas
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-- hold_in.valid ensures that it will get pushed out as soon as src_in.ready
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-- goes high again. This is typically necessary in case of packetized data
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-- where the eop of one packet should not have to wait for the valid (sop)
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-- of a next packet to get pushed out.
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u_hold_val : ENTITY work.dp_hold_ctrl
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PORT MAP (
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rst => rst,
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clk => clk,
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ready => src_in.ready,
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in_ctrl => snk_in.valid,
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hld_ctrl => hold_in.valid
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);
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u_hold_sync : ENTITY work.dp_hold_ctrl
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PORT MAP (
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rst => rst,
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clk => clk,
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ready => src_in.ready,
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in_ctrl => snk_in.sync,
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hld_ctrl => hold_in.sync
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);
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u_hold_sop : ENTITY work.dp_hold_ctrl
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PORT MAP (
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rst => rst,
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clk => clk,
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ready => src_in.ready,
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in_ctrl => snk_in.sop,
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hld_ctrl => hold_in.sop
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);
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u_hold_eop : ENTITY work.dp_hold_ctrl
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PORT MAP (
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rst => rst,
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clk => clk,
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ready => src_in.ready,
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in_ctrl => snk_in.eop,
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hld_ctrl => hold_in.eop
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);
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p_pend_src_out : PROCESS(snk_in, src_out_reg, hold_in)
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BEGIN
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-- Pend data
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IF snk_in.valid='1' THEN
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i_pend_src_out <= snk_in; -- Input data
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ELSE
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i_pend_src_out <= src_out_reg; -- Hold data
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END IF;
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i_pend_src_out.valid <= snk_in.valid OR hold_in.valid;
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i_pend_src_out.sync <= snk_in.sync OR hold_in.sync;
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i_pend_src_out.sop <= snk_in.sop OR hold_in.sop;
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i_pend_src_out.eop <= snk_in.eop OR hold_in.eop;
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END PROCESS;
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p_next_src_out : PROCESS(i_pend_src_out, src_in)
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BEGIN
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-- Next data
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next_src_out <= i_pend_src_out;
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-- Next control
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next_src_out.valid <= i_pend_src_out.valid AND src_in.ready;
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next_src_out.sync <= i_pend_src_out.sync AND src_in.ready;
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next_src_out.sop <= i_pend_src_out.sop AND src_in.ready;
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next_src_out.eop <= i_pend_src_out.eop AND src_in.ready;
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END PROCESS;
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END rtl;
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