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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 [7 : 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 = 8'h00;
- parameter ADDR_CORE_NAME1 = 8'h01;
- parameter ADDR_CORE_TYPE = 8'h02;
- parameter ADDR_CORE_VERSION = 8'h03;
-
- parameter ADDR_BIT_RATE = 8'h10;
- parameter ADDR_DATA_BITS = 8'h11;
- parameter ADDR_STOP_BITS = 8'h12;
-
- // 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 bit 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, 9600 bps
- // Divisor = 50*10E6 / 9600 = 5208
- parameter DEFAULT_BIT_RATE = 16'd5208;
- parameter DEFAULT_DATA_BITS = 4'h8;
- parameter DEFAULT_STOP_BITS = 2'h1;
-
-
- //----------------------------------------------------------------
- // Registers including update variables and write enable.
- //----------------------------------------------------------------
- reg [15 : 0] bit_rate_reg;
- reg [15 : 0] bit_rate_new;
- reg bit_rate_we;
-
- reg [3 : 0] data_bits_reg;
- reg [3 : 0] data_bits_new;
- reg data_bits_we;
-
- reg [1 : 0] stop_bits_reg;
- reg [1 : 0] stop_bits_new;
- reg stop_bits_we;
-
-
- //----------------------------------------------------------------
- // 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_reg),
- .data_bits(data_bits_reg),
- .stop_bits(stop_bits_reg),
-
- // 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
- // asynchronous active low reset.
- //----------------------------------------------------------------
- always @ (posedge clk or negedge reset_n)
- begin: reg_update
- if (!reset_n)
- begin
- bit_rate_reg <= DEFAULT_BIT_RATE;
- data_bits_reg <= DEFAULT_DATA_BITS;
- stop_bits_reg <= DEFAULT_STOP_BITS;
- end
- else
- begin
- if (bit_rate_we)
- begin
- bit_rate_reg <= bit_rate_new;
- end
-
- if (data_bits_we)
- begin
- data_bits_reg <= data_bits_new;
- end
-
- if (stop_bits_we)
- begin
- stop_bits_reg <= stop_bits_new;
- end
-
- end
- end // reg_update
-
-
- //----------------------------------------------------------------
- // api
- //
- // The core API that allows an internal host to control the
- // core functionality.
- //----------------------------------------------------------------
- always @*
- begin: api
- // Default assignments.
- bit_rate_new = 16'h0000;
- bit_rate_we = 0;
- data_bits_new = 4'h0;
- data_bits_we = 0;
- stop_bits_new = 2'b00;
- stop_bits_we = 0;
- tmp_read_data = 32'h00000000;
- tmp_error = 0;
-
- if (cs)
- begin
- if (we)
- begin
- // Write operations.
- case (address)
- ADDR_BIT_RATE:
- begin
- bit_rate_new = write_data[15 : 0];
- bit_rate_we = 1;
- end
-
- ADDR_DATA_BITS:
- begin
- data_bits_new = write_data[3 : 0];
- data_bits_we = 1;
- end
-
- ADDR_STOP_BITS:
- begin
- stop_bits_new = write_data[1 : 0];
- stop_bits_we = 1;
- end
-
- 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
-
- ADDR_BIT_RATE:
- begin
- tmp_read_data = {16'h0000, bit_rate_reg};
- end
-
- ADDR_DATA_BITS:
- begin
- tmp_read_data = {28'h0000000, data_bits_reg};
- end
-
- ADDR_STOP_BITS:
- begin
- tmp_read_data = {30'h0000000, stop_bits_reg};
- end
-
- default:
- begin
- tmp_error = 1;
- end
- endcase // case (address)
- end
- end
- end
-
-endmodule // uart
-
-//======================================================================
-// EOF uart.v
-//======================================================================
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