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//////////////////////////////////////////////////////////////////////
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//// ////
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//// uart_transmitter.v ////
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//// ////
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//// ////
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//// This file is part of the "UART 16550 compatible" project ////
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//// http://www.opencores.org/cores/uart16550/ ////
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//// ////
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//// Documentation related to this project: ////
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//// - http://www.opencores.org/cores/uart16550/ ////
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//// ////
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//// Projects compatibility: ////
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//// - WISHBONE ////
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//// RS232 Protocol ////
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//// 16550D uart (mostly supported) ////
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//// ////
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//// Overview (main Features): ////
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//// UART core transmitter logic ////
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//// ////
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//// Known problems (limits): ////
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//// None known ////
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//// ////
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//// To Do: ////
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//// Thourough testing. ////
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//// ////
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//// Author(s): ////
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//// - gorban@opencores.org ////
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//// - Jacob Gorban ////
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//// - Igor Mohor (igorm@opencores.org) ////
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//// ////
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//// Created: 2001/05/12 ////
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//// Last Updated: 2001/05/17 ////
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//// (See log for the revision history) ////
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//// ////
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//// ////
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//////////////////////////////////////////////////////////////////////
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//// ////
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//// Copyright (C) 2000, 2001 Authors ////
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//// ////
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//// This source file may be used and distributed without ////
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//// restriction provided that this copyright statement is not ////
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//// removed from the file and that any derivative work contains ////
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//// the original copyright notice and the associated disclaimer. ////
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//// ////
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//// This source file is free software; you can redistribute it ////
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//// and/or modify it under the terms of the GNU Lesser General ////
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//// Public License as published by the Free Software Foundation; ////
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//// either version 2.1 of the License, or (at your option) any ////
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//// later version. ////
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//// ////
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//// This source is distributed in the hope that it will be ////
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//// useful, but WITHOUT ANY WARRANTY; without even the implied ////
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//// warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR ////
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//// PURPOSE. See the GNU Lesser General Public License for more ////
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//// details. ////
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//// ////
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//// You should have received a copy of the GNU Lesser General ////
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//// Public License along with this source; if not, download it ////
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//// from http://www.opencores.org/lgpl.shtml ////
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//// ////
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//////////////////////////////////////////////////////////////////////
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//
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// CVS Revision History
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//
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// $Log: not supported by cvs2svn $
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// Revision 1.18 2002/07/22 23:02:23 gorban
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// Bug Fixes:
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// * Possible loss of sync and bad reception of stop bit on slow baud rates fixed.
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// Problem reported by Kenny.Tung.
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// * Bad (or lack of ) loopback handling fixed. Reported by Cherry Withers.
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//
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// Improvements:
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// * Made FIFO's as general inferrable memory where possible.
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// So on FPGA they should be inferred as RAM (Distributed RAM on Xilinx).
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// This saves about 1/3 of the Slice count and reduces P&R and synthesis times.
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//
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// * Added optional baudrate output (baud_o).
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// This is identical to BAUDOUT* signal on 16550 chip.
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// It outputs 16xbit_clock_rate - the divided clock.
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// It's disabled by default. Define UART_HAS_BAUDRATE_OUTPUT to use.
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//
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// Revision 1.16 2002/01/08 11:29:40 mohor
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// tf_pop was too wide. Now it is only 1 clk cycle width.
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//
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// Revision 1.15 2001/12/17 14:46:48 mohor
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// overrun signal was moved to separate block because many sequential lsr
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// reads were preventing data from being written to rx fifo.
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// underrun signal was not used and was removed from the project.
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//
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// Revision 1.14 2001/12/03 21:44:29 gorban
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// Updated specification documentation.
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// Added full 32-bit data bus interface, now as default.
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// Address is 5-bit wide in 32-bit data bus mode.
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// Added wb_sel_i input to the core. It's used in the 32-bit mode.
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// Added debug interface with two 32-bit read-only registers in 32-bit mode.
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// Bits 5 and 6 of LSR are now only cleared on TX FIFO write.
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// My small test bench is modified to work with 32-bit mode.
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//
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// Revision 1.13 2001/11/08 14:54:23 mohor
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// Comments in Slovene language deleted, few small fixes for better work of
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// old tools. IRQs need to be fix.
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//
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// Revision 1.12 2001/11/07 17:51:52 gorban
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// Heavily rewritten interrupt and LSR subsystems.
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// Many bugs hopefully squashed.
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//
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// Revision 1.11 2001/10/29 17:00:46 gorban
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// fixed parity sending and tx_fifo resets over- and underrun
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//
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// Revision 1.10 2001/10/20 09:58:40 gorban
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// Small synopsis fixes
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//
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// Revision 1.9 2001/08/24 21:01:12 mohor
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// Things connected to parity changed.
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// Clock devider changed.
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//
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// Revision 1.8 2001/08/23 16:05:05 mohor
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// Stop bit bug fixed.
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// Parity bug fixed.
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// WISHBONE read cycle bug fixed,
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// OE indicator (Overrun Error) bug fixed.
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// PE indicator (Parity Error) bug fixed.
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// Register read bug fixed.
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//
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// Revision 1.6 2001/06/23 11:21:48 gorban
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// DL made 16-bit long. Fixed transmission/reception bugs.
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//
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// Revision 1.5 2001/06/02 14:28:14 gorban
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// Fixed receiver and transmitter. Major bug fixed.
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//
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// Revision 1.4 2001/05/31 20:08:01 gorban
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// FIFO changes and other corrections.
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//
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// Revision 1.3 2001/05/27 17:37:49 gorban
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// Fixed many bugs. Updated spec. Changed FIFO files structure. See CHANGES.txt file.
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//
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// Revision 1.2 2001/05/21 19:12:02 gorban
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// Corrected some Linter messages.
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//
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// Revision 1.1 2001/05/17 18:34:18 gorban
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// First 'stable' release. Should be sythesizable now. Also added new header.
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//
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// Revision 1.0 2001-05-17 21:27:12+02 jacob
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// Initial revision
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//
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//
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// synopsys translate_off
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`include "timescale.v"
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// synopsys translate_on
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`include "uart_defines.v"
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module uart_transmitter (clk, wb_rst_i, lcr, tf_push, wb_dat_i, enable, stx_pad_o, tstate, tf_count, tx_reset, lsr_mask);
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input clk;
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input wb_rst_i;
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input [7:0] lcr;
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input tf_push;
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input [7:0] wb_dat_i;
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input enable;
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input tx_reset;
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input lsr_mask; //reset of fifo
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output stx_pad_o;
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output [2:0] tstate;
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output [`UART_FIFO_COUNTER_W-1:0] tf_count;
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reg [2:0] tstate;
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reg [4:0] counter;
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reg [2:0] bit_counter; // counts the bits to be sent
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reg [6:0] shift_out; // output shift register
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reg stx_o_tmp;
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reg parity_xor; // parity of the word
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reg tf_pop;
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reg bit_out;
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// TX FIFO instance
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//
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// Transmitter FIFO signals
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wire [`UART_FIFO_WIDTH-1:0] tf_data_in;
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wire [`UART_FIFO_WIDTH-1:0] tf_data_out;
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wire tf_push;
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wire tf_overrun;
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wire [`UART_FIFO_COUNTER_W-1:0] tf_count;
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assign tf_data_in = wb_dat_i;
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uart_tfifo fifo_tx( // error bit signal is not used in transmitter FIFO
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.clk( clk ),
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.wb_rst_i( wb_rst_i ),
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.data_in( tf_data_in ),
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.data_out( tf_data_out ),
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.push( tf_push ),
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.pop( tf_pop ),
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.overrun( tf_overrun ),
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.count( tf_count ),
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.fifo_reset( tx_reset ),
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.reset_status(lsr_mask)
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);
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// TRANSMITTER FINAL STATE MACHINE
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parameter s_idle = 3'd0;
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parameter s_send_start = 3'd1;
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parameter s_send_byte = 3'd2;
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parameter s_send_parity = 3'd3;
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parameter s_send_stop = 3'd4;
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parameter s_pop_byte = 3'd5;
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always @(posedge clk or posedge wb_rst_i)
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begin
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if (wb_rst_i)
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begin
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tstate <= s_idle;
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stx_o_tmp <= 1'b1;
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counter <= 5'b0;
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shift_out <= 7'b0;
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bit_out <= 1'b0;
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parity_xor <= 1'b0;
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tf_pop <= 1'b0;
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bit_counter <= 3'b0;
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end
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else
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if (enable)
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begin
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case (tstate)
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s_idle : if (~|tf_count) // if tf_count==0
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begin
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tstate <= s_idle;
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stx_o_tmp <= 1'b1;
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end
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else
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begin
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tf_pop <= 1'b0;
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stx_o_tmp <= 1'b1;
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tstate <= s_pop_byte;
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end
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s_pop_byte : begin
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tf_pop <= 1'b1;
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case (lcr[/*`UART_LC_BITS*/1:0]) // number of bits in a word
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2'b00 : begin
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bit_counter <= 3'b100;
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parity_xor <= ^tf_data_out[4:0];
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end
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2'b01 : begin
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bit_counter <= 3'b101;
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parity_xor <= ^tf_data_out[5:0];
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end
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2'b10 : begin
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bit_counter <= 3'b110;
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parity_xor <= ^tf_data_out[6:0];
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end
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2'b11 : begin
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bit_counter <= 3'b111;
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parity_xor <= ^tf_data_out[7:0];
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end
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endcase
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{shift_out[6:0], bit_out} <= tf_data_out;
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tstate <= s_send_start;
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end
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s_send_start : begin
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tf_pop <= 1'b0;
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if (~|counter)
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counter <= 5'b01111;
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else
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if (counter == 5'b00001)
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begin
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counter <= 0;
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tstate <= s_send_byte;
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end
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else
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counter <= counter - 1'b1;
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stx_o_tmp <= 1'b0;
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end
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s_send_byte : begin
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if (~|counter)
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counter <= 5'b01111;
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else
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if (counter == 5'b00001)
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begin
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if (bit_counter > 3'b0)
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begin
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bit_counter <= bit_counter - 1'b1;
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{shift_out[5:0],bit_out } <= {shift_out[6:1], shift_out[0]};
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tstate <= s_send_byte;
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end
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else // end of byte
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if (~lcr[`UART_LC_PE])
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begin
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tstate <= s_send_stop;
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end
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else
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begin
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case ({lcr[`UART_LC_EP],lcr[`UART_LC_SP]})
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2'b00: bit_out <= ~parity_xor;
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2'b01: bit_out <= 1'b1;
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2'b10: bit_out <= parity_xor;
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2'b11: bit_out <= 1'b0;
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endcase
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tstate <= s_send_parity;
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end
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counter <= 0;
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end
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else
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counter <= counter - 1'b1;
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stx_o_tmp <= bit_out; // set output pin
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end
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s_send_parity : begin
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if (~|counter)
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counter <= 5'b01111;
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else
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if (counter == 5'b00001)
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begin
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counter <= 4'b0;
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tstate <= s_send_stop;
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end
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else
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counter <= counter - 1'b1;
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stx_o_tmp <= bit_out;
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end
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s_send_stop : begin
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if (~|counter)
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begin
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casex ({lcr[`UART_LC_SB],lcr[`UART_LC_BITS]})
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3'b0xx: counter <= 5'b01101; // 1 stop bit ok igor
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3'b100: counter <= 5'b10101; // 1.5 stop bit
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default: counter <= 5'b11101; // 2 stop bits
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endcase
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end
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else
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if (counter == 5'b00001)
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begin
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counter <= 0;
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tstate <= s_idle;
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end
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else
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counter <= counter - 1'b1;
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stx_o_tmp <= 1'b1;
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end
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default : // should never get here
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tstate <= s_idle;
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endcase
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end // end if enable
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else
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tf_pop <= 1'b0; // tf_pop must be 1 cycle width
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end // transmitter logic
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assign stx_pad_o = lcr[`UART_LC_BC] ? 1'b0 : stx_o_tmp; // Break condition
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endmodule
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