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//======================================================================
//
// uart.v
// ------
// Top level wrapper for the uart core.
//
// A simple universal asynchronous receiver/transmitter (UART)
// interface. The interface contains 16 byte wide transmit and
// receivea buffers and can handle start and stop bits. But in
// general is rather simple. The primary purpose is as host
// interface for the coretest design. The core also has a
// loopback mode to allow testing of a serial link.
//
// Note that the UART has a separate API interface to allow
// a control core to change settings such as speed. But the core
// has default values to allow it to start operating directly
// after reset. No config should be needed.
//
//
// Author: Joachim Strombergson
// Copyright (c) 2014 SUNET
//
// Redistribution and use in source and binary forms, with or
// without modification, are permitted provided that the following
// conditions are met:
//
// 1. Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
//
// 2. Redistributions in binary form must reproduce the above copyright
// notice, this list of conditions and the following disclaimer in
// the documentation and/or other materials provided with the
// distribution.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
// FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
// COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
// INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
// BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
// LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
// CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
// STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
// ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
//
//======================================================================
module uart(
input wire clk,
input wire reset_n,
// External interface.
input wire rxd,
output wire txd,
// Internal receive interface.
output wire rxd_syn,
output [7 : 0] rxd_data,
input wire rxd_ack,
// Internal transmit interface.
input wire txd_syn,
input wire [7 : 0] txd_data,
output wire txd_ack,
// API interface.
input wire cs,
input wire we,
input wire [3 : 0] address,
input wire [31 : 0] write_data,
output wire [31 : 0] read_data,
output wire error,
// Debug output.
output wire [7 : 0] debug
);
//----------------------------------------------------------------
// Internal constant and parameter definitions.
//----------------------------------------------------------------
// API addresses.
parameter ADDR_CORE_NAME0 = 4'h0;
parameter ADDR_CORE_NAME1 = 4'h1;
parameter ADDR_CORE_TYPE = 4'h2;
parameter ADDR_CORE_VERSION = 4'h3;
// Core ID constants.
parameter CORE_NAME0 = 32'h75617274; // "uart"
parameter CORE_NAME1 = 32'h20202020; // " "
parameter CORE_TYPE = 32'h20202031; // " 1"
parameter CORE_VERSION = 32'h302e3031; // "0.01"
// The default clock rate is based on target clock frequency
// divided by the bit rate times in order to hit the
// center of the bits. I.e.
// Clock: 50 MHz
// Bitrate: 19200 bps
// Divisor = 50*10E6 / 9600 = 5208
parameter DEFAULT_CLK_RATE = 16'd5208;
parameter DEFAULT_HALF_CLK_RATE = DEFAULT_CLK_RATE / 2;
parameter DEFAULT_DATA_BITS = 4'h8;
parameter DEFAULT_STOP_BITS = 2'h2;
//----------------------------------------------------------------
// Registers including update variables and write enable.
//----------------------------------------------------------------
//----------------------------------------------------------------
// Wires.
//----------------------------------------------------------------
wire [15 : 0] bit_rate;
wire [1 : 0] stop_bits;
wire core_rxd;
wire core_txd;
wire core_rxd_syn;
wire [7 : 0] core_rxd_data;
wire core_rxd_ack;
wire core_txd_syn;
wire [7 : 0] core_txd_data;
wire core_txd_ack;
reg [31 : 0] tmp_read_data;
reg tmp_error;
//----------------------------------------------------------------
// Concurrent connectivity for ports etc.
//----------------------------------------------------------------
assign txd = core_txd;
assign core_rxd = rxd;
assign rxd_syn = core_rxd_syn;
assign rxd_data = core_rxd_data;
assign core_rxd_ack = rxd_ack;
assign core_txd_syn = txd_syn;
assign core_txd_data = txd_data;
assign txd_ack = core_txd_ack;
assign read_data = tmp_read_data;
assign error = tmp_error;
assign debug = core_rxd_data;
//----------------------------------------------------------------
// core
//
// Instantiation of the uart core.
//----------------------------------------------------------------
uart_core core(
.clk(clk),
.reset_n(reset_n),
// Configuration parameters
.bit_rate(bit_rate),
.stop_bits(stop_bits),
// External data interface
.rxd(core_rxd),
.txd(core_txd),
// Internal receive interface.
.rxd_syn(core_rxd_syn),
.rxd_data(core_rxd_data),
.rxd_ack(core_rxd_ack),
// Internal transmit interface.
.txd_syn(core_txd_syn),
.txd_data(core_txd_data),
.txd_ack(core_txd_ack)
);
//----------------------------------------------------------------
// reg_update
//
// Update functionality for all registers in the core.
// All registers are positive edge triggered with synchronous
// active low reset. All registers have write enable.
//----------------------------------------------------------------
always @ (posedge clk)
begin: reg_update
if (!reset_n)
begin
end
else
begin
end
end // reg_update
//----------------------------------------------------------------
// api
//
// The core API that allows an internal host to control the
// core functionality.
//----------------------------------------------------------------
always @*
begin: api
// Default assignments.
tmp_read_data = 32'h00000000;
tmp_error = 0;
if (cs)
begin
if (we)
begin
// Write operations.
case (address)
default:
begin
tmp_error = 1;
end
endcase // case (address)
end
else
begin
// Read operations.
case (address)
ADDR_CORE_NAME0:
begin
tmp_read_data = CORE_NAME0;
end
ADDR_CORE_NAME1:
begin
tmp_read_data = CORE_NAME1;
end
ADDR_CORE_TYPE:
begin
tmp_read_data = CORE_TYPE;
end
ADDR_CORE_VERSION:
begin
tmp_read_data = CORE_VERSION;
end
default:
begin
tmp_error = 1;
end
endcase // case (address)
end
end
end
endmodule // uart
//======================================================================
// EOF uart.v
//======================================================================
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