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////////////////////////////////////////////////////////////////////////////////
//
// Filename:    rxuart.v
//
// Project:     XuLA2 board
//
// Purpose:     Receive and decode inputs from a single UART line.
//
//      To interface with this module, connect it to your system clock,
//      pass it the 32 bit setup register (defined below) and the UART
//      input.  When data becomes available, the o_wr line will be asserted
//      for one clock cycle.  On parity or frame errors, the o_parity_err
//      or o_frame_err lines will be asserted.  Likewise, on a break 
//      condition, o_break will be asserted.  These lines are self clearing.
//
//      There is a synchronous reset line, logic high.
//
//      Now for the setup register.  The register is 32 bits, so that this
//      UART may be set up over a 32-bit bus.
//
//      i_setup[29:28]  Indicates the number of data bits per word.  This will
//      either be 2'b00 for an 8-bit word, 2'b01 for a 7-bit word, 2'b10
//      for a six bit word, or 2'b11 for a five bit word.
//
//      i_setup[27]     Indicates whether or not to use one or two stop bits.
//              Set this to one to expect two stop bits, zero for one.
//
//      i_setup[26]     Indicates whether or not a parity bit exists.  Set this
//              to 1'b1 to include parity.
//
//      i_setup[25]     Indicates whether or not the parity bit is fixed.  Set
//              to 1'b1 to include a fixed bit of parity, 1'b0 to allow the
//              parity to be set based upon data.  (Both assume the parity
//              enable value is set.)
//
//      i_setup[24]     This bit is ignored if parity is not used.  Otherwise,
//              in the case of a fixed parity bit, this bit indicates whether
//              mark (1'b1) or space (1'b0) parity is used.  Likewise if the
//              parity is not fixed, a 1'b1 selects even parity, and 1'b0
//              selects odd.
//
//      i_setup[23:0]   Indicates the speed of the UART in terms of clocks.
//              So, for example, if you have a 200 MHz clock and wish to
//              run your UART at 9600 baud, you would take 200 MHz and divide
//              by 9600 to set this value to 24'd20834.  Likewise if you wished
//              to run this serial port at 115200 baud from a 200 MHz clock,
//              you would set the value to 24'd1736
//
//      Thus, to set the UART for the common setting of an 8-bit word, 
//      one stop bit, no parity, and 115200 baud over a 200 MHz clock, you
//      would want to set the setup value to:
//
//      32'h0006c8              // For 115,200 baud, 8 bit, no parity
//      32'h005161              // For 9600 baud, 8 bit, no parity
//      
//
//
// Creator:     Dan Gisselquist, Ph.D.
//              Gisselquist Technology, LLC
//
////////////////////////////////////////////////////////////////////////////////
//
// Copyright (C) 2015, 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.
//
// License:     GPL, v3, as defined and found on www.gnu.org,
//              http://www.gnu.org/licenses/gpl.html
//
//
////////////////////////////////////////////////////////////////////////////////
//
//
 
// States: (@ baud counter == 0)
//      0        First bit arrives
//      ..7     Bits arrive
//      8       Stop bit (x1)
//      9       Stop bit (x2)
///     c       break condition
//      d       Waiting for the channel to go high
//      e       Waiting for the reset to complete
//      f       Idle state
`define RXU_BIT_ZERO            4'h0
`define RXU_BIT_ONE             4'h1
`define RXU_BIT_TWO             4'h2
`define RXU_BIT_THREE           4'h3
`define RXU_BIT_FOUR            4'h4
`define RXU_BIT_FIVE            4'h5
`define RXU_BIT_SIX             4'h6
`define RXU_BIT_SEVEN           4'h7
`define RXU_PARITY              4'h8
`define RXU_STOP                4'h9
`define RXU_SECOND_STOP         4'ha
// Unused 4'hb
// Unused 4'hc
`define RXU_BREAK               4'hd
`define RXU_RESET_IDLE          4'he
`define RXU_IDLE                4'hf
 
module rxuart(i_clk, i_reset, i_setup, i_uart, o_wr, o_data, o_break,
                        o_parity_err, o_frame_err, o_ck_uart);
        //  parameter // CLOCKS_PER_BAUD = 25'd004340,
                        //  BREAK_CONDITION = CLOCKS_PER_BAUD * 12,
                        //  CLOCKS_PER_HALF_BAUD = CLOCKS_PER_BAUD/2;
        // 8 data bits, no parity, (at least 1) stop bit
        input                   i_clk, i_reset;
        input           [29:0]   i_setup;
        input                   i_uart;
        output  reg             o_wr;
        output  reg     [7:0]    o_data;
        output  reg             o_break;
        output  reg             o_parity_err, o_frame_err;
        output  wire            o_ck_uart;
 
 
        wire    [27:0]   clocks_per_baud, break_condition, half_baud;
        wire    [1:0]    data_bits;
        wire            use_parity, parity_even, dblstop, fixd_parity;
        reg     [29:0]   r_setup;
        assign  clocks_per_baud = { 4'h0, r_setup[23:0] };
        assign  data_bits   = r_setup[29:28];
        assign  dblstop     = r_setup[27];
        assign  use_parity  = r_setup[26];
        assign  fixd_parity = r_setup[25];
        assign  parity_even = r_setup[24];
        assign  break_condition = { r_setup[23:0], 4'h0 };
        assign  half_baud = { 5'h00, r_setup[23:1] };
 
        reg     q_uart, qq_uart, ck_uart;
        initial q_uart  = 1'b0;
        initial qq_uart = 1'b0;
        initial ck_uart = 1'b0;
        always @(posedge i_clk)
        begin
                q_uart <= i_uart;
                qq_uart <= q_uart;
                ck_uart <= qq_uart;
        end
        assign  o_ck_uart = ck_uart;
 
        reg     [27:0]   chg_counter;
        initial chg_counter = 28'h00;
        always @(posedge i_clk)
                if (i_reset)
                        chg_counter <= 28'h00;
                else if (qq_uart != ck_uart)
                        chg_counter <= 28'h00;
                else if (chg_counter < break_condition)
                        chg_counter <= chg_counter + 1;
 
        always @(posedge i_clk)
                o_break <=((chg_counter >= break_condition)&&(~ck_uart))? 1'b1:1'b0;
 
        reg     [3:0]    state;
        reg     [27:0]   baud_counter;
        reg     [7:0]    data_reg;
        reg             calc_parity;
        initial o_wr = 1'b0;
        initial state = `RXU_RESET_IDLE;
        initial o_parity_err = 1'b0;
        initial o_frame_err  = 1'b0;
        // initial      baud_counter = clocks_per_baud;
        always @(posedge i_clk)
        begin
                if (i_reset)
                begin
                        o_wr <= 1'b0;
                        o_data <= 8'h00;
                        state <= `RXU_RESET_IDLE;
                        baud_counter <= clocks_per_baud; // Set, not reset
                        data_reg <= 8'h00;
                        calc_parity <= 1'b0;
                        o_parity_err <= 1'b0;
                        o_frame_err <= 1'b0;
                end else if (state == `RXU_RESET_IDLE)
                begin
                        r_setup <= i_setup;
                        data_reg <= 8'h00; o_data <= 8'h00; o_wr <= 1'b0;
                        baud_counter <= clocks_per_baud-28'h01;// Set, not reset
                        if ((ck_uart)&&(chg_counter >= break_condition))
                                // Goto idle state from a reset
                                state <= `RXU_IDLE;
                        else // Otherwise, stay in this condition 'til reset
                                state <= `RXU_RESET_IDLE;
                        calc_parity <= 1'b0;
                        o_parity_err <= 1'b0;
                        o_frame_err <= 1'b0;
                end else if ((~ck_uart)&&(chg_counter >= break_condition))
                begin // We are in a break condition
                        state <= `RXU_BREAK;
                        o_wr <= 1'b0;
                        o_data <= 8'h00;
                        baud_counter <= clocks_per_baud-28'h01;// Set, not reset
                        data_reg <= 8'h00;
                        calc_parity <= 1'b0;
                        o_parity_err <= 1'b0;
                        o_frame_err <= 1'b0;
                        r_setup <= i_setup;
                end else if (state == `RXU_BREAK)
                begin // Goto idle state following return ck_uart going high
                        data_reg <= 8'h00; o_data <= 8'h00; o_wr <= 1'b0;
                        baud_counter <= clocks_per_baud - 28'h01;
                        if (ck_uart)
                                state <= `RXU_IDLE;
                        else
                                state <= `RXU_BREAK;
                        calc_parity <= 1'b0;
                        o_parity_err <= 1'b0;
                        o_frame_err <= 1'b0;
                        r_setup <= i_setup;
                end else if (state == `RXU_IDLE)
                begin // Idle state, independent of baud counter
                        data_reg <= 8'h00; o_data <= 8'h00; o_wr <= 1'b0;
                        baud_counter <= clocks_per_baud - 28'h01;
                        if ((ck_uart == 1'b0)&&(chg_counter > half_baud))
                        begin
                                // We are in the center of a valid start bit
                                case (data_bits)
                                2'b00: state <= `RXU_BIT_ZERO;
                                2'b01: state <= `RXU_BIT_ONE;
                                2'b10: state <= `RXU_BIT_TWO;
                                2'b11: state <= `RXU_BIT_THREE;
                                endcase
                        end else // Otherwise, just stay here in idle
                                state <= `RXU_IDLE;
                        calc_parity <= 1'b0;
                        o_parity_err <= 1'b0;
                        o_frame_err <= 1'b0;
                end else if (baud_counter == 0)
                begin
                        baud_counter <= clocks_per_baud-28'h1;
                        if (state < `RXU_BIT_SEVEN)
                        begin
                                // Data arrives least significant bit first.
                                // By the time this is clocked in, it's what
                                // you'll have.
                                data_reg <= { ck_uart, data_reg[7:1] };
                                calc_parity <= calc_parity ^ ck_uart;
                                o_data <= 8'h00;
                                o_wr <= 1'b0;
                                state <= state + 1;
                                o_parity_err <= 1'b0;
                                o_frame_err <= 1'b0;
                        end else if (state == `RXU_BIT_SEVEN)
                        begin
                                data_reg <= { ck_uart, data_reg[7:1] };
                                calc_parity <= calc_parity ^ ck_uart;
                                o_data <= 8'h00;
                                o_wr <= 1'b0;
                                state <= (use_parity) ? `RXU_PARITY:`RXU_STOP;
                                o_parity_err <= 1'b0;
                                o_frame_err <= 1'b0;
                        end else if (state == `RXU_PARITY)
                        begin
                                if (fixd_parity)
                                        o_parity_err <= (ck_uart ^ parity_even);
                                else
                                        o_parity_err <= ((parity_even && (calc_parity != ck_uart))
                                                ||((~parity_even)&&(calc_parity==ck_uart)));
                                state <= `RXU_STOP;
                                o_frame_err <= 1'b0;
                        end else if (state == `RXU_STOP)
                        begin // Stop (or parity) bit(s)
                                case (data_bits)
                                2'b00: o_data <= data_reg;
                                2'b01: o_data <= { 1'b0, data_reg[7:1] };
                                2'b10: o_data <= { 2'b0, data_reg[7:2] };
                                2'b11: o_data <= { 3'b0, data_reg[7:3] };
                                endcase
                                o_wr <= 1'b1; // Pulse the write
                                o_frame_err <= (~ck_uart);
                                if (~ck_uart)
                                        state <= `RXU_RESET_IDLE;
                                else if (dblstop)
                                        state <= `RXU_SECOND_STOP;
                                else
                                        state <= `RXU_IDLE;
                                // o_parity_err <= 1'b0;
                        end else // state must equal RX_SECOND_STOP
                        begin
                                if (~ck_uart)
                                begin
                                        o_frame_err <= 1'b1;
                                        state <= `RXU_RESET_IDLE;
                                end else begin
                                        state <= `RXU_IDLE;
                                        o_frame_err  <= 1'b0;
                                end
                                o_parity_err <= 1'b0;
                        end
                end else begin
                        o_wr <= 1'b0;   // data_reg = data_reg
                        baud_counter <= baud_counter - 1;
                        o_parity_err <= 1'b0;
                        o_frame_err  <= 1'b0;
                end
        end
 
endmodule
 
 

Line No.	Rev	Author	Line
1	7	dgisselq	`////////////////////////////////////////////////////////////////////////////////`
2	2	dgisselq	`//`
3			`// Filename: rxuart.v`
4			`//`
5	7	dgisselq	`// Project: XuLA2 board`
6	2	dgisselq	`//`
7			`// Purpose: Receive and decode inputs from a single UART line.`
8			`//`
9			`// To interface with this module, connect it to your system clock,`
10			`// pass it the 32 bit setup register (defined below) and the UART`
11			`// input. When data becomes available, the o_wr line will be asserted`
12			`// for one clock cycle. On parity or frame errors, the o_parity_err`
13			`// or o_frame_err lines will be asserted. Likewise, on a break`
14			`// condition, o_break will be asserted. These lines are self clearing.`
15			`//`
16			`// There is a synchronous reset line, logic high.`
17			`//`
18			`// Now for the setup register. The register is 32 bits, so that this`
19			`// UART may be set up over a 32-bit bus.`
20			`//`
21			`// i_setup[29:28] Indicates the number of data bits per word. This will`
22			`// either be 2'b00 for an 8-bit word, 2'b01 for a 7-bit word, 2'b10`
23			`// for a six bit word, or 2'b11 for a five bit word.`
24			`//`
25			`// i_setup[27] Indicates whether or not to use one or two stop bits.`
26			`// Set this to one to expect two stop bits, zero for one.`
27			`//`
28			`// i_setup[26] Indicates whether or not a parity bit exists. Set this`
29			`// to 1'b1 to include parity.`
30			`//`
31			`// i_setup[25] Indicates whether or not the parity bit is fixed. Set`
32			`// to 1'b1 to include a fixed bit of parity, 1'b0 to allow the`
33			`// parity to be set based upon data. (Both assume the parity`
34			`// enable value is set.)`
35			`//`
36			`// i_setup[24] This bit is ignored if parity is not used. Otherwise,`
37			`// in the case of a fixed parity bit, this bit indicates whether`
38			`// mark (1'b1) or space (1'b0) parity is used. Likewise if the`
39			`// parity is not fixed, a 1'b1 selects even parity, and 1'b0`
40			`// selects odd.`
41			`//`
42			`// i_setup[23:0] Indicates the speed of the UART in terms of clocks.`
43			`// So, for example, if you have a 200 MHz clock and wish to`
44			`// run your UART at 9600 baud, you would take 200 MHz and divide`
45			`// by 9600 to set this value to 24'd20834. Likewise if you wished`
46			`// to run this serial port at 115200 baud from a 200 MHz clock,`
47			`// you would set the value to 24'd1736`
48			`//`
49			`// Thus, to set the UART for the common setting of an 8-bit word,`
50			`// one stop bit, no parity, and 115200 baud over a 200 MHz clock, you`
51			`// would want to set the setup value to:`
52			`//`
53			`// 32'h0006c8 // For 115,200 baud, 8 bit, no parity`
54			`// 32'h005161 // For 9600 baud, 8 bit, no parity`
55			`//`
56	7	dgisselq	`//`
57			`//`
58			`// Creator: Dan Gisselquist, Ph.D.`
59	2	dgisselq	`// Gisselquist Technology, LLC`
60			`//`
61	7	dgisselq	`////////////////////////////////////////////////////////////////////////////////`
62	2	dgisselq	`//`
63	7	dgisselq	`// Copyright (C) 2015, Gisselquist Technology, LLC`
64	2	dgisselq	`//`
65	7	dgisselq	`// This program is free software (firmware): you can redistribute it and/or`
66			`// modify it under the terms of the GNU General Public License as published`
67			`// by the Free Software Foundation, either version 3 of the License, or (at`
68			`// your option) any later version.`
69	2	dgisselq	`//`
70	7	dgisselq	`// This program is distributed in the hope that it will be useful, but WITHOUT`
71			`// ANY WARRANTY; without even the implied warranty of MERCHANTIBILITY or`
72			`// FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License`
73			`// for more details.`
74	2	dgisselq	`//`
75	7	dgisselq	`// License: GPL, v3, as defined and found on www.gnu.org,`
76			`// http://www.gnu.org/licenses/gpl.html`
77	2	dgisselq	`//`
78	7	dgisselq	`//`
79			`////////////////////////////////////////////////////////////////////////////////`
80			`//`
81			`//`
82	2	dgisselq
83			`// States: (@ baud counter == 0)`
84			`// 0 First bit arrives`
85			`// ..7 Bits arrive`
86			`// 8 Stop bit (x1)`
87			`// 9 Stop bit (x2)`
88			`/// c break condition`
89			`// d Waiting for the channel to go high`
90			`// e Waiting for the reset to complete`
91			`// f Idle state`
92			`define RXU_BIT_ZERO 4'h0
93			`define RXU_BIT_ONE 4'h1
94			`define RXU_BIT_TWO 4'h2
95			`define RXU_BIT_THREE 4'h3
96			`define RXU_BIT_FOUR 4'h4
97			`define RXU_BIT_FIVE 4'h5
98			`define RXU_BIT_SIX 4'h6
99			`define RXU_BIT_SEVEN 4'h7
100			`define RXU_PARITY 4'h8
101			`define RXU_STOP 4'h9
102			`define RXU_SECOND_STOP 4'ha
103			`// Unused 4'hb`
104			`// Unused 4'hc`
105			`define RXU_BREAK 4'hd
106			`define RXU_RESET_IDLE 4'he
107			`define RXU_IDLE 4'hf
108
109			`module rxuart(i_clk, i_reset, i_setup, i_uart, o_wr, o_data, o_break,`
110			`o_parity_err, o_frame_err, o_ck_uart);`
111			`// parameter // CLOCKS_PER_BAUD = 25'd004340,`
112			`// BREAK_CONDITION = CLOCKS_PER_BAUD * 12,`
113			`// CLOCKS_PER_HALF_BAUD = CLOCKS_PER_BAUD/2;`
114			`// 8 data bits, no parity, (at least 1) stop bit`
115			`input i_clk, i_reset;`
116			`input [29:0] i_setup;`
117			`input i_uart;`
118			`output reg o_wr;`
119			`output reg [7:0] o_data;`
120			`output reg o_break;`
121			`output reg o_parity_err, o_frame_err;`
122			`output wire o_ck_uart;`
123
124
125			`wire [27:0] clocks_per_baud, break_condition, half_baud;`
126			`wire [1:0] data_bits;`
127			`wire use_parity, parity_even, dblstop, fixd_parity;`
128			`reg [29:0] r_setup;`
129			`assign clocks_per_baud = { 4'h0, r_setup[23:0] };`
130			`assign data_bits = r_setup[29:28];`
131			`assign dblstop = r_setup[27];`
132			`assign use_parity = r_setup[26];`
133			`assign fixd_parity = r_setup[25];`
134			`assign parity_even = r_setup[24];`
135			`assign break_condition = { r_setup[23:0], 4'h0 };`
136			`assign half_baud = { 5'h00, r_setup[23:1] };`
137
138			`reg q_uart, qq_uart, ck_uart;`
139			`initial q_uart = 1'b0;`
140			`initial qq_uart = 1'b0;`
141			`initial ck_uart = 1'b0;`
142			`always @(posedge i_clk)`
143			`begin`
144			`q_uart <= i_uart;`
145			`qq_uart <= q_uart;`
146			`ck_uart <= qq_uart;`
147			`end`
148			`assign o_ck_uart = ck_uart;`
149
150			`reg [27:0] chg_counter;`
151			`initial chg_counter = 28'h00;`
152			`always @(posedge i_clk)`
153			`if (i_reset)`
154			`chg_counter <= 28'h00;`
155			`else if (qq_uart != ck_uart)`
156			`chg_counter <= 28'h00;`
157			`else if (chg_counter < break_condition)`
158			`chg_counter <= chg_counter + 1;`
159
160			`always @(posedge i_clk)`
161			`o_break <=((chg_counter >= break_condition)&&(~ck_uart))? 1'b1:1'b0;`
162
163			`reg [3:0] state;`
164			`reg [27:0] baud_counter;`
165			`reg [7:0] data_reg;`
166			`reg calc_parity;`
167			`initial o_wr = 1'b0;`
168			initial state = `RXU_RESET_IDLE;
169			`initial o_parity_err = 1'b0;`
170			`initial o_frame_err = 1'b0;`
171			`// initial baud_counter = clocks_per_baud;`
172			`always @(posedge i_clk)`
173			`begin`
174			`if (i_reset)`
175			`begin`
176			`o_wr <= 1'b0;`
177			`o_data <= 8'h00;`
178			state <= `RXU_RESET_IDLE;
179			`baud_counter <= clocks_per_baud; // Set, not reset`
180			`data_reg <= 8'h00;`
181			`calc_parity <= 1'b0;`
182			`o_parity_err <= 1'b0;`
183			`o_frame_err <= 1'b0;`
184			end else if (state == `RXU_RESET_IDLE)
185			`begin`
186			`r_setup <= i_setup;`
187			`data_reg <= 8'h00; o_data <= 8'h00; o_wr <= 1'b0;`
188			`baud_counter <= clocks_per_baud-28'h01;// Set, not reset`
189			`if ((ck_uart)&&(chg_counter >= break_condition))`
190			`// Goto idle state from a reset`
191			state <= `RXU_IDLE;
192			`else // Otherwise, stay in this condition 'til reset`
193			state <= `RXU_RESET_IDLE;
194			`calc_parity <= 1'b0;`
195			`o_parity_err <= 1'b0;`
196			`o_frame_err <= 1'b0;`
197			`end else if ((~ck_uart)&&(chg_counter >= break_condition))`
198			`begin // We are in a break condition`
199			state <= `RXU_BREAK;
200			`o_wr <= 1'b0;`
201			`o_data <= 8'h00;`
202			`baud_counter <= clocks_per_baud-28'h01;// Set, not reset`
203			`data_reg <= 8'h00;`
204			`calc_parity <= 1'b0;`
205			`o_parity_err <= 1'b0;`
206			`o_frame_err <= 1'b0;`
207			`r_setup <= i_setup;`
208			end else if (state == `RXU_BREAK)
209			`begin // Goto idle state following return ck_uart going high`
210			`data_reg <= 8'h00; o_data <= 8'h00; o_wr <= 1'b0;`
211			`baud_counter <= clocks_per_baud - 28'h01;`
212			`if (ck_uart)`
213			state <= `RXU_IDLE;
214			`else`
215			state <= `RXU_BREAK;
216			`calc_parity <= 1'b0;`
217			`o_parity_err <= 1'b0;`
218			`o_frame_err <= 1'b0;`
219			`r_setup <= i_setup;`
220			end else if (state == `RXU_IDLE)
221			`begin // Idle state, independent of baud counter`
222			`data_reg <= 8'h00; o_data <= 8'h00; o_wr <= 1'b0;`
223			`baud_counter <= clocks_per_baud - 28'h01;`
224			`if ((ck_uart == 1'b0)&&(chg_counter > half_baud))`
225			`begin`
226			`// We are in the center of a valid start bit`
227			`case (data_bits)`
228			2'b00: state <= `RXU_BIT_ZERO;
229			2'b01: state <= `RXU_BIT_ONE;
230			2'b10: state <= `RXU_BIT_TWO;
231			2'b11: state <= `RXU_BIT_THREE;
232			`endcase`
233			`end else // Otherwise, just stay here in idle`
234			state <= `RXU_IDLE;
235			`calc_parity <= 1'b0;`
236			`o_parity_err <= 1'b0;`
237			`o_frame_err <= 1'b0;`
238			`end else if (baud_counter == 0)`
239			`begin`
240			`baud_counter <= clocks_per_baud-28'h1;`
241			if (state < `RXU_BIT_SEVEN)
242			`begin`
243			`// Data arrives least significant bit first.`
244			`// By the time this is clocked in, it's what`
245			`// you'll have.`
246			`data_reg <= { ck_uart, data_reg[7:1] };`
247			`calc_parity <= calc_parity ^ ck_uart;`
248			`o_data <= 8'h00;`
249			`o_wr <= 1'b0;`
250			`state <= state + 1;`
251			`o_parity_err <= 1'b0;`
252			`o_frame_err <= 1'b0;`
253			end else if (state == `RXU_BIT_SEVEN)
254			`begin`
255			`data_reg <= { ck_uart, data_reg[7:1] };`
256			`calc_parity <= calc_parity ^ ck_uart;`
257			`o_data <= 8'h00;`
258			`o_wr <= 1'b0;`
259			state <= (use_parity) ? `RXU_PARITY:`RXU_STOP;
260			`o_parity_err <= 1'b0;`
261			`o_frame_err <= 1'b0;`
262			end else if (state == `RXU_PARITY)
263			`begin`
264			`if (fixd_parity)`
265			`o_parity_err <= (ck_uart ^ parity_even);`
266			`else`
267			`o_parity_err <= ((parity_even && (calc_parity != ck_uart))`
268			`\|\|((~parity_even)&&(calc_parity==ck_uart)));`
269			state <= `RXU_STOP;
270			`o_frame_err <= 1'b0;`
271			end else if (state == `RXU_STOP)
272			`begin // Stop (or parity) bit(s)`
273			`case (data_bits)`
274			`2'b00: o_data <= data_reg;`
275			`2'b01: o_data <= { 1'b0, data_reg[7:1] };`
276			`2'b10: o_data <= { 2'b0, data_reg[7:2] };`
277			`2'b11: o_data <= { 3'b0, data_reg[7:3] };`
278			`endcase`
279			`o_wr <= 1'b1; // Pulse the write`
280			`o_frame_err <= (~ck_uart);`
281			`if (~ck_uart)`
282			state <= `RXU_RESET_IDLE;
283			`else if (dblstop)`
284			state <= `RXU_SECOND_STOP;
285			`else`
286			state <= `RXU_IDLE;
287			`// o_parity_err <= 1'b0;`
288			`end else // state must equal RX_SECOND_STOP`
289			`begin`
290			`if (~ck_uart)`
291			`begin`
292			`o_frame_err <= 1'b1;`
293			state <= `RXU_RESET_IDLE;
294			`end else begin`
295			state <= `RXU_IDLE;
296			`o_frame_err <= 1'b0;`
297			`end`
298			`o_parity_err <= 1'b0;`
299			`end`
300			`end else begin`
301			`o_wr <= 1'b0; // data_reg = data_reg`
302			`baud_counter <= baud_counter - 1;`
303			`o_parity_err <= 1'b0;`
304			`o_frame_err <= 1'b0;`
305			`end`
306			`end`
307
308			`endmodule`
309
310

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