Subversion Repositories wbuart32

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

//

// Filename:    linetest.v

//

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

//

// Purpose:     To test that the txuart and rxuart modules work properly, by

//              buffering one line's worth of input, and then piping that line

//      to the transmitter while (possibly) receiving a new line.

//

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

//      run as a top-level testing file, requiring only the transmit and receive

//      UART pins and the clock 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  linetest(i_clk,

`ifndef OPT_STANDALONE

                        i_setup,

`endif

                        i_uart_rx, o_uart_tx);

        input           i_clk;

`ifndef OPT_STANDALONE

        input   [30:0]   i_setup;

`endif

        input           i_uart_rx;

        output  wire    o_uart_tx;

        // If i_setup isnt set up as an input parameter, it needs to be set.

        // We do so here, to a setting appropriate to create a 115200 Baud

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

        // data word, 1-stop bit, and no parity.

`ifdef  OPT_STANDALONE

        wire    [30:0]   i_setup;

        assign          i_setup = 31'd868;      // 115200 Baud, if clk @ 100MHz

`endif

        reg     [7:0]    buffer  [0:255];

        reg     [7:0]    head, tail;

        // Create a reset line that will always be true on a power on reset

        reg     pwr_reset;

        initial pwr_reset = 1'b1;

        always @(posedge i_clk)

                pwr_reset = 1'b0;

        // The UART Receiver

        //

        // This is where everything begins, by reading data from the UART.

        //

        // Data (rx_data) is present when rx_stb is true.  Any parity or

        // frame errors will also be valid at that time.  Finally, we'll ignore

        // errors, and even the clocked uart input distributed from here.

        wire    rx_stb, rx_break, rx_perr, rx_ferr, rx_ignored;

        wire    [7:0]    rx_data;

        rxuart  receiver(i_clk, pwr_reset, i_setup, i_uart_rx, rx_stb, rx_data,

                        rx_break, rx_perr, rx_ferr, rx_ignored);

        // The next step in this process is to dump everything we read into a 

        // FIFO.  First step: writing into the FIFO.  Always write into FIFO

        // memory.  (The next step will step the memory address if rx_stb was

        // true ...)

        wire    [7:0]    nxt_head;

        assign  nxt_head = head + 8'h01;

        always @(posedge i_clk)

                buffer[head] <= rx_data;

        // Select where in our FIFO memory to write.  On reset, we clear the 

        // memory.  In all other cases/respects, we step the memory forward.

        //

        // However ... we won't step it forward IF ...

        //      rx_break        - we are in a BREAK condition on the line

        //              (i.e. ... it's disconnected)

        //      rx_perr         - We've seen a parity error

        //      rx_ferr         - Same thing for a frame error

        //      nxt_head != tail - If the FIFO is already full, we'll just drop

        //              this new value, rather than dumping random garbage

        //              from the FIFO until we go round again ...  i.e., we

        //              don't write on potential overflow.

        //

        // Adjusting this address will make certain that the next write to the

        // FIFO goes to the next address--since we've already written the FIFO

        // memory at this address.

        initial head= 8'h00;

        always @(posedge i_clk)

                if (pwr_reset)

                        head <= 8'h00;

                else if ((rx_stb)&&(!rx_break)&&(!rx_perr)&&(!rx_ferr)&&(nxt_head != tail))

                        head <= nxt_head;

        wire    [7:0]    nused;

        reg     [7:0]    lineend;

        reg             run_tx;

        // How much of the FIFO is in use?  head - tail.  What if they wrap

        // around?  Still: head-tail, but this time truncated to the number of

        // bits of interest.  It can never be negative ... so ... we're good,

        // this just measures that number.

        assign  nused = head-tail;

        // Here's the guts of the algorithm--setting run_tx.  Once set, the

        // buffer will flush.  Here, we set it on one of two conditions: 1)

        // a newline is received, or 2) the line is now longer than 80

        // characters.

        //

        // Once the line has ben transmitted (separate from emptying the buffer)

        // we stop transmitting.

        initial run_tx = 0;

        initial lineend = 0;

        always @(posedge i_clk)

                if (pwr_reset)

                begin

                        run_tx <= 1'b0;

                        lineend <= 8'h00;

                end else if(((rx_data == 8'h0a)||(rx_data == 8'hd))&&(rx_stb))

                begin

                        // Start transmitting once we get to either a newline

                        // or a carriage return character

                        lineend <= head+8'h1;

                        run_tx <= 1'b1;

                end else if ((!run_tx)&&(nused>8'd80))

                begin

                        // Start transmitting once we get to 80 chars

                        lineend <= head;

                        run_tx <= 1'b1;

                end else if (tail == lineend)

                        // Line buffer has been emptied

                        run_tx <= 1'b0;

        // Now ... let's deal with the transmitter

        wire    tx_break, tx_busy;

        assign  tx_break = 1'b0;

        reg     [7:0]    tx_data;

        reg             tx_stb;

        // When do we wish to transmit?

        //

        // Any time run_tx is true--but we'll give it an extra clock.

        initial tx_stb = 1'b0;

        always @(posedge i_clk)

                tx_stb <= run_tx;

        // We'll transmit the data from our FIFO from ... wherever our tail

        // is pointed.

        always @(posedge i_clk)

                tx_data <= buffer[tail];

        // We increment the pointer to where we read from any time 1) we are

        // requesting to transmit a character, and 2) the transmitter was not

        // busy and thus accepted our request.  At that time, increment the

        // pointer, and we'll be ready for another round.

        initial tail = 8'h00;

        always @(posedge i_clk)

                if(pwr_reset)

                        tail <= 8'h00;

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

                        tail <= tail + 8'h01;

        // Bypass any hardwaare 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