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//////////////////////////////////////////////////////////////////////////////
// SPDX-FileCopyrightText: 2021 , Dinesh Annayya
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// SPDX-License-Identifier: Apache-2.0
// SPDX-FileContributor: Created by Dinesh Annayya <dinesha@opencores.org>
//
//////////////////////////////////////////////////////////////////////
//// ////
//// UART RX FSM ////
//// ////
//// This file is part of the YIFive cores project ////
//// https://github.com/dineshannayya/yifive_r0.git ////
//// http://www.opencores.org/cores/yifive/ ////
//// ////
//// Description ////
//// ////
//// To Do: ////
//// nothing ////
//// ////
//// Author(s): ////
//// - Dinesh Annayya, dinesha@opencores.org ////
//// ////
//// Revision : ////
//// 0.1 - 20th June 2021, Dinesh A ////
//// 1. initial version picked from ////
//// http://www.opencores.org/cores/oms8051mini ////
//// ////
//////////////////////////////////////////////////////////////////////
//// ////
//// Copyright (C) 2000 Authors and OPENCORES.ORG ////
//// ////
//// This source file may be used and distributed without ////
//// restriction provided that this copyright statement is not ////
//// removed from the file and that any derivative work contains ////
//// the original copyright notice and the associated disclaimer. ////
//// ////
//// This source file is free software; you can redistribute it ////
//// and/or modify it under the terms of the GNU Lesser General ////
//// Public License as published by the Free Software Foundation; ////
//// either version 2.1 of the License, or (at your option) any ////
//// later version. ////
//// ////
//// This source 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 Lesser General Public License for more ////
//// details. ////
//// ////
//// You should have received a copy of the GNU Lesser General ////
//// Public License along with this source; if not, download it ////
//// from http://www.opencores.org/lgpl.shtml ////
//// ////
//////////////////////////////////////////////////////////////////////
module uart_rxfsm (
reset_n ,
baud_clk_16x ,
cfg_rx_enable ,
cfg_stop_bit ,
cfg_pri_mod ,
error_ind ,
// FIFO control signal
fifo_aval ,
fifo_wr ,
fifo_data ,
// Line Interface
si
);
input reset_n ; // active low reset signal
input baud_clk_16x ; // baud clock-16x
input cfg_rx_enable ; // transmit interface enable
input cfg_stop_bit ; // stop bit
// 0 --> 1 stop, 1 --> 2 Stop
input [1:0] cfg_pri_mod ;// Priority Mode
// 2'b00 --> None
// 2'b10 --> Even priority
// 2'b11 --> Odd priority
output [1:0] error_ind ; // 2'b00 --> Normal
// 2'b01 --> framing error
// 2'b10 --> parity error
// 2'b11 --> fifo full
//--------------------------------------
// FIFO control signal
//--------------------------------------
input fifo_aval ; // fifo empty
output fifo_wr ; // fifo write, assumed no back to back write
output [7:0] fifo_data ; // fifo write data
// Line Interface
input si ; // rxd pin
reg [7:0] fifo_data ; // fifo write data
reg fifo_wr ; // fifo write
reg [1:0] error_ind ;
reg [2:0] cnt ;
reg [3:0] offset ; // free-running counter from 0 - 15
reg [3:0] rxpos ; // stable rx position
reg [2:0] rxstate ;
parameter idle_st = 3'b000;
parameter xfr_start = 3'b001;
parameter xfr_data_st = 3'b010;
parameter xfr_pri_st = 3'b011;
parameter xfr_stop_st1 = 3'b100;
parameter xfr_stop_st2 = 3'b101;
always @(negedge reset_n or posedge baud_clk_16x) begin
if(reset_n == 0) begin
rxstate <= 3'b0;
offset <= 4'b0;
rxpos <= 4'b0;
cnt <= 3'b0;
error_ind <= 2'b0;
fifo_wr <= 1'b0;
fifo_data <= 8'h0;
end
else begin
offset <= offset + 1;
case(rxstate)
idle_st : begin
if(!si) begin // Start indication
if(fifo_aval && cfg_rx_enable) begin
rxstate <= xfr_start;
cnt <= 0;
rxpos <= offset + 8; // Assign center rxoffset
error_ind <= 2'b00;
end
else begin
error_ind <= 2'b11; // fifo full error indication
end
end else begin
error_ind <= 2'b00; // Reset Error
end
end
xfr_start : begin
// Make Sure that minimum 8 cycle low is detected
if(cnt < 7 && si) begin // Start indication
rxstate <= idle_st;
end
else if(cnt == 7 && !si) begin // Start indication
rxstate <= xfr_data_st;
cnt <= 0;
end else begin
cnt <= cnt +1;
end
end
xfr_data_st : begin
if(rxpos == offset) begin
fifo_data[cnt] <= si;
cnt <= cnt+1;
if(cnt == 7) begin
fifo_wr <= 1;
if(cfg_pri_mod == 2'b00) // No Priority
rxstate <= xfr_stop_st1;
else rxstate <= xfr_pri_st;
end
end
end
xfr_pri_st : begin
fifo_wr <= 0;
if(rxpos == offset) begin
if(cfg_pri_mod == 2'b10) // even priority
if( si != ^fifo_data) error_ind <= 2'b10;
else // Odd Priority
if( si != ~(^fifo_data)) error_ind <= 2'b10;
rxstate <= xfr_stop_st1;
end
end
xfr_stop_st1 : begin
fifo_wr <= 0;
if(rxpos == offset) begin
if(si) begin
if(cfg_stop_bit) // Two Stop bit
rxstate <= xfr_stop_st2;
else
rxstate <= idle_st;
end else begin // Framing error
error_ind <= 2'b01;
rxstate <= idle_st;
end
end
end
xfr_stop_st2 : begin
if(rxpos == offset) begin
if(si) begin
rxstate <= idle_st;
end else begin // Framing error
error_ind <= 2'b01;
rxstate <= idle_st;
end
end
end
default: rxstate <= idle_st;
endcase
end
end
endmodule