2022-09-19 02:51:11 -04:00
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//======================================================================
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//
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// uart.v
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// ------
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// Top level wrapper for the uart core.
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//
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// A simple universal asynchronous receiver/transmitter (UART)
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// interface. The interface contains 16 byte wide transmit and
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// receivea buffers and can handle start and stop bits. But in
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// general is rather simple. The primary purpose is as host
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// interface for the coretest design. The core also has a
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// loopback mode to allow testing of a serial link.
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//
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// Note that the UART has a separate API interface to allow
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// a control core to change settings such as speed. But the core
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// has default values to allow it to start operating directly
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// after reset. No config should be needed.
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//
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//
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// Author: Joachim Strombergson
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// Copyright (c) 2014, Secworks Sweden AB
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// SPDX-License-Identifier: BSD-2-Clause
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//
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// Redistribution and use in source and binary forms, with or
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// without modification, are permitted provided that the following
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// conditions are met:
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//
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// 1. Redistributions of source code must retain the above copyright
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// notice, this list of conditions and the following disclaimer.
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//
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// 2. Redistributions in binary form must reproduce the above copyright
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// notice, this list of conditions and the following disclaimer in
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// the documentation and/or other materials provided with the
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// distribution.
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//
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// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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// FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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// COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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// INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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// BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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// LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
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// CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
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// STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
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// ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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//
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//======================================================================
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module uart(
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input wire clk,
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input wire reset_n,
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input wire rxd,
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output wire txd,
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input wire cs,
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input wire we,
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input wire [7 : 0] address,
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2022-10-06 07:23:30 -04:00
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/* verilator lint_off UNUSED */
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2022-09-19 02:51:11 -04:00
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input wire [31 : 0] write_data,
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2022-10-06 07:23:30 -04:00
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/* verilator lint_on UNUSED */
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2022-09-19 02:51:11 -04:00
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output wire [31 : 0] read_data,
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output wire ready
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);
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//----------------------------------------------------------------
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// Internal constant and parameter definitions.
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//----------------------------------------------------------------
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localparam ADDR_BIT_RATE = 8'h10;
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localparam ADDR_DATA_BITS = 8'h11;
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localparam ADDR_STOP_BITS = 8'h12;
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localparam ADDR_RX_STATUS = 8'h20;
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localparam ADDR_RX_DATA = 8'h21;
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localparam ADDR_TX_STATUS = 8'h40;
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localparam ADDR_TX_DATA = 8'h41;
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// The default bit rate is based on target clock frequency
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// divided by the bit rate times in order to hit the
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// center of the bits. I.e.
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2022-10-19 09:32:55 -04:00
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// Clock: 18 MHz, 62500 bps
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// Divisor = 18E6 / 62500 = 288
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// This also satisfies 1E6 % bps == 0 for the CH552 MCU used for USB-serial
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localparam DEFAULT_BIT_RATE = 16'd288;
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2022-09-19 02:51:11 -04:00
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localparam DEFAULT_DATA_BITS = 4'h8;
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localparam DEFAULT_STOP_BITS = 2'h1;
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//----------------------------------------------------------------
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// Registers including update variables and write enable.
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//----------------------------------------------------------------
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reg [15 : 0] bit_rate_reg;
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reg bit_rate_we;
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reg [3 : 0] data_bits_reg;
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reg data_bits_we;
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reg [1 : 0] stop_bits_reg;
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reg stop_bits_we;
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//----------------------------------------------------------------
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// Wires.
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//----------------------------------------------------------------
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wire core_rxd_syn;
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wire [7 : 0] core_rxd_data;
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wire core_rxd_ack;
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reg core_txd_syn;
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reg [7 : 0] core_txd_data;
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wire core_txd_ready;
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wire fifo_out_syn;
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wire [7 : 0] fifo_out_data;
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reg fifo_out_ack;
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reg [31 : 0] tmp_read_data;
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reg tmp_ready;
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//----------------------------------------------------------------
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// Concurrent connectivity for ports etc.
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//----------------------------------------------------------------
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assign read_data = tmp_read_data;
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assign ready = tmp_ready;
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//----------------------------------------------------------------
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// Module instantiations.
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//----------------------------------------------------------------
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uart_core core(
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.clk(clk),
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.reset_n(reset_n),
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// Configuration parameters
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.bit_rate(bit_rate_reg),
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.data_bits(data_bits_reg),
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.stop_bits(stop_bits_reg),
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// External data interface
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.rxd(rxd),
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.txd(txd),
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// Internal receive interface.
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.rxd_syn(core_rxd_syn),
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.rxd_data(core_rxd_data),
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.rxd_ack(core_rxd_ack),
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// Internal transmit interface.
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.txd_syn(core_txd_syn),
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.txd_data(core_txd_data),
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.txd_ready(core_txd_ready)
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);
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uart_fifo fifo(
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.clk(clk),
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.reset_n(reset_n),
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.in_syn(core_rxd_syn),
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.in_data(core_rxd_data),
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.in_ack(core_rxd_ack),
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.out_syn(fifo_out_syn),
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.out_data(fifo_out_data),
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.out_ack(fifo_out_ack)
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);
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//----------------------------------------------------------------
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// reg_update
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//
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// Update functionality for all registers in the core.
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// All registers are positive edge triggered with synchronous
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// active low reset.
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//----------------------------------------------------------------
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always @ (posedge clk)
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begin: reg_update
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if (!reset_n) begin
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bit_rate_reg <= DEFAULT_BIT_RATE;
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data_bits_reg <= DEFAULT_DATA_BITS;
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stop_bits_reg <= DEFAULT_STOP_BITS;
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end
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else begin
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if (bit_rate_we) begin
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bit_rate_reg <= write_data[15 : 0];
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end
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if (data_bits_we) begin
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data_bits_reg <= write_data[3 : 0];
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end
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if (stop_bits_we) begin
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stop_bits_reg <= write_data[1 : 0];
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end
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end
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end // reg_update
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//----------------------------------------------------------------
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// api
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//
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// The core API that allows an internal host to control the
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// core functionality.
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//----------------------------------------------------------------
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always @*
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begin: api
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// Default assignments.
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bit_rate_we = 1'h0;
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data_bits_we = 1'h0;
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stop_bits_we = 1'h0;
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core_txd_syn = 1'h0;
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fifo_out_ack = 1'h0;
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tmp_read_data = 32'h0;
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tmp_ready = 1'h0;
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core_txd_data = write_data[7 : 0];
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if (cs) begin
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tmp_ready = 1'h1;
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if (we) begin
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case (address)
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ADDR_BIT_RATE: begin
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bit_rate_we = 1;
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end
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ADDR_DATA_BITS: begin
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data_bits_we = 1;
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end
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ADDR_STOP_BITS: begin
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stop_bits_we = 1;
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end
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ADDR_TX_DATA: begin
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core_txd_syn = 1'h1;
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end
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default: begin
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end
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endcase // case (address)
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end
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else begin
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case (address)
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ADDR_BIT_RATE: begin
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tmp_read_data = {16'h0, bit_rate_reg};
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end
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ADDR_DATA_BITS: begin
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tmp_read_data = {28'h0, data_bits_reg};
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end
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ADDR_STOP_BITS: begin
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tmp_read_data = {30'h0, stop_bits_reg};
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end
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ADDR_RX_STATUS: begin
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tmp_read_data = {31'h0, fifo_out_syn};
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end
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ADDR_RX_DATA: begin
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fifo_out_ack = 1'h1;
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tmp_read_data = {24'h0, fifo_out_data};
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end
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ADDR_TX_STATUS: begin
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tmp_read_data = {31'h0, core_txd_ready};
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end
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default: begin
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end
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endcase // case (address)
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end
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end
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end
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endmodule // uart
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//======================================================================
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// EOF uart.v
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//======================================================================
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