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//
// Copyright 2011-2013 Ettus Research LLC
// Copyright 2018 Ettus Research, a National Instruments Company
//
// SPDX-License-Identifier: LGPL-3.0-or-later
//
module simple_uart_rx
#(parameter SIZE=8)
(input clk, input rst,
output [7:0] fifo_out, input fifo_read, output [15:0] fifo_level, output fifo_empty,
input [15:0] clkdiv, input rx);
reg rx_d1, rx_d2;
always @(posedge clk)
if(rst)
{rx_d2,rx_d1} <= 0;
else
{rx_d2,rx_d1} <= {rx_d1,rx};
reg [15:0] baud_ctr;
reg [3:0] bit_ctr;
reg [7:0] sr;
wire neg_trans = rx_d2 & ~rx_d1;
wire shift_now = baud_ctr == (clkdiv>>1);
wire stop_now = (bit_ctr == 10) && shift_now;
wire go_now = (bit_ctr == 0) && neg_trans;
always @(posedge clk)
if(rst)
sr <= 0;
else if(shift_now)
sr <= {rx_d2,sr[7:1]};
always @(posedge clk)
if(rst)
baud_ctr <= 0;
else
if(go_now)
baud_ctr <= 1;
else if(stop_now)
baud_ctr <= 0;
else if(baud_ctr >= clkdiv)
baud_ctr <= 1;
else if(baud_ctr != 0)
baud_ctr <= baud_ctr + 1;
always @(posedge clk)
if(rst)
bit_ctr <= 0;
else
if(go_now)
bit_ctr <= 1;
else if(stop_now)
bit_ctr <= 0;
else if(baud_ctr == clkdiv)
bit_ctr <= bit_ctr + 1;
wire i_tready, o_tvalid;
wire full = ~i_tready;
wire write = ~full & stop_now;
assign fifo_empty = ~o_tvalid;
axi_fifo #(.WIDTH(8), .SIZE(SIZE)) fifo
(.clk(clk),.reset(rst), .clear(1'b0),
.i_tdata(sr),.i_tvalid(write),.i_tready(i_tready),
.o_tdata(fifo_out),.o_tvalid(o_tvalid),.o_tready(fifo_read),
.space(),.occupied(fifo_level) );
endmodule // simple_uart_rx
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