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// 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
// <> for a copy.
// License: GPL, v3, as defined and found on,
// 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.
// Two versions of the UART can be found in the rtl directory: a full featured
// UART, and a LITE UART that only handles 8N1 -- no break sending, break
// detection, parity error detection, etc. If we set USE_LITE_UART here, those
// simplified UART modules will be used.
// `define USE_LITE_UART
module linetest(i_clk,
i_uart_rx, o_uart_tx);
input i_clk;
input [30:0] i_setup;
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.
wire [30:0] i_setup;
assign i_setup = 31'd868; // 115200 Baud, if clk @ 100MHz
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;
/* verilator lint_off UNUSED */
wire rx_ignored;
/* verilator lint_on UNUSED */
wire [7:0] rx_data;
rxuartlite #(24'd868)
receiver(i_clk, i_uart_rx, rx_stb, 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)
run_tx <= 1'b0;
lineend <= 8'h00;
end else if(((rx_data == 8'h0a)||(rx_data == 8'hd))&&(rx_stb))
// 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))
// 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)
tail <= 8'h00;
else if ((tx_stb)&&(!tx_busy))
tail <= tail + 8'h01;
// Bypass any hardwaare flow control
wire cts_n;
assign cts_n = 1'b0;
txuartlite #(24'd868)
transmitter(i_clk, tx_stb, tx_data, o_uart_tx, tx_busy);
txuart transmitter(i_clk, pwr_reset, i_setup, tx_break,
tx_stb, tx_data, cts_n, o_uart_tx, tx_busy);