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//
// Copyright 2011-2013 Ettus Research LLC
//
// This program is free software: 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
// MERCHANTABILITY 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. If not, see <http://www.gnu.org/licenses/>.
//
module simple_uart_tx
#(parameter SIZE=0)
(input clk, input rst,
input [7:0] fifo_in, input fifo_write, output [5:0] fifo_level, output fifo_full,
input [15:0] clkdiv, output baudclk, output reg tx);
reg [15:0] baud_ctr;
reg [3:0] bit_ctr;
wire read, empty;
wire [7:0] char_to_send;
wire i_tready, o_tvalid;
assign fifo_full = ~i_tready;
assign empty = ~o_tvalid;
axi_fifo #(.WIDTH(8), .SIZE(SIZE)) fifo
(.clk(clk),.reset(rst), .clear(1'b0),
.i_tdata(fifo_in), .i_tvalid(fifo_write), .i_tready(i_tready),
.o_tdata(char_to_send),.o_tvalid(o_tvalid),.o_tready(read),
.space(fifo_level),.occupied() );
always @(posedge clk)
if(rst)
baud_ctr <= 0;
else if (baud_ctr >= clkdiv)
baud_ctr <= 0;
else
baud_ctr <= baud_ctr + 1;
always @(posedge clk)
if(rst)
bit_ctr <= 0;
else if(baud_ctr == clkdiv)
if(bit_ctr == 10)
bit_ctr <= 0;
else if(bit_ctr != 0)
bit_ctr <= bit_ctr + 1;
else if(~empty)
bit_ctr <= 1;
always @(posedge clk)
if(rst)
tx <= 1;
else
case(bit_ctr)
0 : tx <= 1;
1 : tx <= 0;
2 : tx <= char_to_send[0];
3 : tx <= char_to_send[1];
4 : tx <= char_to_send[2];
5 : tx <= char_to_send[3];
6 : tx <= char_to_send[4];
7 : tx <= char_to_send[5];
8 : tx <= char_to_send[6];
9 : tx <= char_to_send[7];
default : tx <= 1;
endcase // case(bit_ctr)
assign read = (bit_ctr == 9) && (baud_ctr == clkdiv);
assign baudclk = (baud_ctr == 1); // Only for debug purposes
endmodule // simple_uart_tx
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