Subversion Repositories wbuart32

////////////////////////////////////////////////////////////////////////////////

//

// Filename:    helloworld.v

//

// Project:     wbuart32, a full featured UART with simulator

//

// Purpose:     To create a *very* simple UART test program, which can be used

//              as the top level design file of any FPGA program.

//

//      With some modifications (discussed below), this RTL should be able to

//      run as a top-level testing file, requiring only the UART and clock pin

//      to work.

//

// Creator:     Dan Gisselquist, Ph.D.

//              Gisselquist Technology, LLC

//

////////////////////////////////////////////////////////////////////////////////

//

// Copyright (C) 2015-2016, Gisselquist Technology, LLC

//

// This program is free software (firmware): you can redistribute it and/or

// modify it under the terms of  the GNU General Public License as published

// by the Free Software Foundation, either version 3 of the License, or (at

// your option) any later version.

//

// This program is distributed in the hope that it will be useful, but WITHOUT

// ANY WARRANTY; without even the implied warranty of MERCHANTIBILITY or

// FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

// for more details.

//

// You should have received a copy of the GNU General Public License along

// with this program.  (It's in the $(ROOT)/doc directory, run make with no

// target there if the PDF file isn't present.)  If not, see

// <http://www.gnu.org/licenses/> for a copy.

//

// License:     GPL, v3, as defined and found on www.gnu.org,

//              http://www.gnu.org/licenses/gpl.html

//

//

////////////////////////////////////////////////////////////////////////////////

//

//

// One issue with the design is how to set the values of the setup register.

// (*This is a comment, not a verilator attribute ... )  Verilator needs to

// know/set those values in order to work.  However, this design can also be

// used as a stand-alone top level configuration file.  In this latter case,

// the setup register needs to be set internal to the file.  Here, we use

// OPT_STANDALONE to distinguish between the two.  If set, the file runs under

// (* Another comment still ...) Verilator and we need to get i_setup from the

// external environment.  If not, it must be set internally.

//

`ifndef VERILATOR

`define OPT_STANDALONE

`endif

//

module  helloworld(i_clk,

`ifndef OPT_STANDALONE

                        i_setup,

`endif

                        o_uart_tx);

        input           i_clk;

        output  wire    o_uart_tx;

        // Here we set i_setup to something appropriate to create a 115200 Baud

        // UART system from a 100MHz clock.  This also sets us to an 8-bit data

        // word, 1-stop bit, and no parity.  This will be overwritten by

        // i_setup, but at least it gives us something to start with/from.

        parameter       INITIAL_UART_SETUP = 31'd868;

        // The i_setup wires are input when run under Verilator, but need to

        // be set internally if this is going to run as a standalone top level

        // test configuration.

`ifdef  OPT_STANDALONE

        wire    [30:0]   i_setup;

        assign  i_setup = INITIAL_UART_SETUP;

`else

        input   [30:0]   i_setup;

`endif

        reg     pwr_reset;

        initial pwr_reset = 1'b1;

        always @(posedge i_clk)

                pwr_reset <= 1'b0;

        reg     [7:0]    message [0:15];

        initial begin

                message[ 0] = "H";

                message[ 1] = "e";

                message[ 2] = "l";

                message[ 3] = "l";

                message[ 4] = "o";

                message[ 5] = ",";

                message[ 6] = " ";

                message[ 7] = "W";

                message[ 8] = "o";

                message[ 9] = "r";

                message[10] = "l";

                message[11] = "d";

                message[12] = "!";

                message[13] = " ";

                message[14] = "\r";

                message[15] = "\n";

        end

        reg     [27:0]   counter;

        initial counter = 28'hffffff0;

        always @(posedge i_clk)

                counter <= counter + 1'b1;

        wire            tx_break, tx_busy;

        reg             tx_stb;

        reg     [3:0]    tx_index;

        reg     [7:0]    tx_data;

        assign  tx_break = 1'b0;

        initial tx_index = 4'h0;

        always @(posedge i_clk)

                if ((tx_stb)&&(!tx_busy))

                        tx_index <= tx_index + 1'b1;

        always @(posedge i_clk)

                tx_data <= message[tx_index];

        initial tx_stb = 1'b0;

        always @(posedge i_clk)

                if (&counter)

                        tx_stb <= 1'b1;

                else if ((tx_stb)&&(!tx_busy)&&(tx_index==4'hf))

                        tx_stb <= 1'b0;

        // Bypass any hardware flow control

        wire    rts;

        assign  rts = 1'b1;

        txuart  transmitter(i_clk, pwr_reset, i_setup, tx_break,

                        tx_stb, tx_data, rts, o_uart_tx, tx_busy);

endmodule