//-----------------------------------------------------------------
//                       USB Serial Port
//                            V0.1
//                     Ultra-Embedded.com
//                       Copyright 2020
//
//                 Email: admin@ultra-embedded.com
//
//                         License: LGPL
//-----------------------------------------------------------------
//
// 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, write to the
// Free Software Foundation, Inc., 59 Temple Place, Suite 330,
// Boston, MA  02111-1307  USA
//-----------------------------------------------------------------

//-----------------------------------------------------------------
//                          Generated File
//-----------------------------------------------------------------

module usb_cdc_top
//-----------------------------------------------------------------
// Params
//-----------------------------------------------------------------
#(
     parameter BAUDRATE         = 115200
)
//-----------------------------------------------------------------
// Ports
//-----------------------------------------------------------------
(
     input	   clk_i,
     input	   rst_i,

     output [7:0]  utmi_data_out_o,
     output	   utmi_txvalid_o,
     output [1:0]  utmi_op_mode_o,
     output [1:0]  utmi_xcvrselect_o,
     output	   utmi_termselect_o,
     output	   utmi_dppulldown_o,
     output	   utmi_dmpulldown_o,

     input [7:0]   utmi_data_in_i,
     input	   utmi_txready_i,
     input	   utmi_rxvalid_i,
     input	   utmi_rxactive_i,
     input	   utmi_rxerror_i,
     input [1:0]   utmi_linestate_i,

     input	   sys_clk,
     input	   cpu_valid,
     input [15:0]  cpu_addr,
     output [31:0] cpu_rdata,
     input [31:0]  cpu_wdata,
     input [3:0]   cpu_wstrb,

     input	   tx_i,
     output	   rx_o,
     output	   rx_break_o
);

wire  [  7:0]  usb_rx_data_w;
wire           usb_tx_accept_w;
wire           enable_w = 1'h1;
wire           usb_tx_valid_w;
wire           usb_rx_accept_w;
wire  [  7:0]  usb_tx_data_w;
wire           usb_rx_valid_w;
wire           usb_rx_break_w;

usb_cdc_core
u_usb
(
    // Inputs
     .clk_i(clk_i)
    ,.rst_i(rst_i)
    ,.enable_i(enable_w)
    ,.utmi_data_in_i(utmi_data_in_i)
    ,.utmi_txready_i(utmi_txready_i)
    ,.utmi_rxvalid_i(utmi_rxvalid_i)
    ,.utmi_rxactive_i(utmi_rxactive_i)
    ,.utmi_rxerror_i(utmi_rxerror_i)
    ,.utmi_linestate_i(utmi_linestate_i)
    ,.inport_valid_i(usb_tx_valid_w)
    ,.inport_data_i(usb_tx_data_w)
    ,.outport_accept_i(usb_rx_accept_w)

    // Outputs
    ,.utmi_data_out_o(utmi_data_out_o)
    ,.utmi_txvalid_o(utmi_txvalid_o)
    ,.utmi_op_mode_o(utmi_op_mode_o)
    ,.utmi_xcvrselect_o(utmi_xcvrselect_o)
    ,.utmi_termselect_o(utmi_termselect_o)
    ,.utmi_dppulldown_o(utmi_dppulldown_o)
    ,.utmi_dmpulldown_o(utmi_dmpulldown_o)
    ,.inport_accept_o(usb_tx_accept_w)
    ,.outport_valid_o(usb_rx_valid_w)
    ,.outport_data_o(usb_rx_data_w)
    ,.outport_break_o(usb_rx_break_w),

 // CPU bus
 .sys_clk           ( sys_clk ),
 .cpu_valid         ( cpu_valid ),
 .cpu_addr          ( cpu_addr ),
 .cpu_rdata         ( cpu_rdata ),
 .cpu_wdata         ( cpu_wdata ),
 .cpu_wstrb         ( cpu_wstrb )
);

//-----------------------------------------------------------------
// Output FIFO
//-----------------------------------------------------------------
wire       tx_valid_w;
wire [7:0] tx_data_w;
wire       tx_accept_w;

usb_cdc_fifo
#(
    .WIDTH(8),
    .DEPTH(512),
    .ADDR_W(9)
)
u_fifo_tx
(
    .clk_i(clk_i),
    .rst_i(rst_i),

    // In
    .push_i(tx_valid_w),
    .data_in_i(tx_data_w),
    .accept_o(tx_accept_w),

    // Out
    .pop_i(usb_tx_accept_w),
    .data_out_o(usb_tx_data_w),
    .valid_o(usb_tx_valid_w)
);

//-----------------------------------------------------------------
// Input FIFO
//-----------------------------------------------------------------
wire       rx_valid_w;
wire [7:0] rx_data_w;
wire       rx_accept_w;

usb_cdc_fifo
#(
    .WIDTH(8),
    .DEPTH(512),
    .ADDR_W(9)
)
u_fifo_rx
(
    .clk_i(clk_i),
    .rst_i(rst_i),

    // In
    .push_i(usb_rx_valid_w),
    .data_in_i(usb_rx_data_w),
    .accept_o(usb_rx_accept_w),

    // Out
    .pop_i(rx_accept_w),
    .data_out_o(rx_data_w),
    .valid_o(rx_valid_w)
);

//-----------------------------------------------------------------
// Registers
//-----------------------------------------------------------------

// Configuration
localparam   STOP_BITS = 1'b0; // 0 = 1, 1 = 2
localparam   CLK_FREQ  = 48000000;
localparam   BIT_DIV   = (CLK_FREQ / BAUDRATE) - 1;

localparam   START_BIT = 4'd0;
localparam   STOP_BIT0 = 4'd9;
localparam   STOP_BIT1 = 4'd10;

// TX Signals
reg          tx_busy_q;
reg [3:0]    tx_bits_q;
reg [31:0]   tx_count_q;
reg [7:0]    tx_shift_reg_q;
reg          txd_q;

// RX Signals
reg          rxd_q;
reg [7:0]    rx_data_q;
reg [3:0]    rx_bits_q;
reg [31:0]   rx_count_q;
reg [7:0]    rx_shift_reg_q;
reg          rx_ready_q;
reg          rx_busy_q;

reg          rx_err_q;

//-----------------------------------------------------------------
// Re-sync RXD
//-----------------------------------------------------------------
reg rxd_ms_q;

always @ (posedge clk_i or posedge rst_i)
if (rst_i)
begin
   rxd_ms_q <= 1'b1;
   rxd_q    <= 1'b1;
end
else
begin
   rxd_ms_q <= tx_i;
   rxd_q    <= rxd_ms_q;
end

//-----------------------------------------------------------------
// RX Clock Divider
//-----------------------------------------------------------------
wire rx_sample_w = (rx_count_q == 32'b0);

always @ (posedge clk_i or posedge rst_i)
if (rst_i)
    rx_count_q        <= 32'b0;
else
begin
    // Inactive
    if (!rx_busy_q)
        rx_count_q    <= {1'b0, BIT_DIV[31:1]};
    // Rx bit timer
    else if (rx_count_q != 0)
        rx_count_q    <= (rx_count_q - 1);
    // Active
    else if (rx_sample_w)
    begin
        // Last bit?
        if ((rx_bits_q == STOP_BIT0 && !STOP_BITS) || (rx_bits_q == STOP_BIT1 && STOP_BITS))
            rx_count_q    <= 32'b0;
        else
            rx_count_q    <= BIT_DIV;
    end
end

//-----------------------------------------------------------------
// RX Shift Register
//-----------------------------------------------------------------
always @ (posedge clk_i or posedge rst_i)
if (rst_i)
begin
    rx_shift_reg_q <= 8'h00;
    rx_busy_q      <= 1'b0;
end
// Rx busy
else if (rx_busy_q && rx_sample_w)
begin
    // Last bit?
    if (rx_bits_q == STOP_BIT0 && !STOP_BITS)
        rx_busy_q <= 1'b0;
    else if (rx_bits_q == STOP_BIT1 && STOP_BITS)
        rx_busy_q <= 1'b0;
    else if (rx_bits_q == START_BIT)
    begin
        // Start bit should still be low as sampling mid
        // way through start bit, so if high, error!
        if (rxd_q)
            rx_busy_q <= 1'b0;
    end
    // Rx shift register
    else
        rx_shift_reg_q <= {rxd_q, rx_shift_reg_q[7:1]};
end
// Start bit?
else if (!rx_busy_q && rxd_q == 1'b0)
begin
    rx_shift_reg_q <= 8'h00;
    rx_busy_q      <= 1'b1;
end

always @ (posedge clk_i or posedge rst_i)
if (rst_i)
    rx_bits_q  <= START_BIT;
else if (rx_sample_w && rx_busy_q)
begin
    if ((rx_bits_q == STOP_BIT1 && STOP_BITS) || (rx_bits_q == STOP_BIT0 && !STOP_BITS))
        rx_bits_q <= START_BIT;
    else
        rx_bits_q <= rx_bits_q + 4'd1;
end
else if (!rx_busy_q && (BIT_DIV == 32'b0))
    rx_bits_q  <= START_BIT + 4'd1;
else if (!rx_busy_q)
    rx_bits_q  <= START_BIT;

//-----------------------------------------------------------------
// RX Data
//-----------------------------------------------------------------
always @ (posedge clk_i or posedge rst_i)
if (rst_i)
begin
   rx_ready_q      <= 1'b0;
   rx_data_q       <= 8'h00;
   rx_err_q        <= 1'b0;
end
else
begin
   // If reading data, reset data state
   if (tx_accept_w)
   begin
       rx_ready_q <= 1'b0;
       rx_err_q   <= 1'b0;
   end

   if (rx_busy_q && rx_sample_w)
   begin
       // Stop bit
       if ((rx_bits_q == STOP_BIT1 && STOP_BITS) || (rx_bits_q == STOP_BIT0 && !STOP_BITS))
       begin
           // RXD should be still high
           if (rxd_q)
           begin
               rx_data_q      <= rx_shift_reg_q;
               rx_ready_q     <= 1'b1;
           end
           // Bad Stop bit - wait for a full bit period
           // before allowing start bit detection again
           else
           begin
               rx_ready_q      <= 1'b0;
               rx_data_q       <= 8'h00;
               rx_err_q        <= 1'b1;
           end
       end
       // Mid start bit sample - if high then error
       else if (rx_bits_q == START_BIT && rxd_q)
           rx_err_q        <= 1'b1;
   end
end

assign tx_data_w   = rx_data_q;
assign tx_valid_w  = rx_ready_q;

//-----------------------------------------------------------------
// TX Clock Divider
//-----------------------------------------------------------------
wire tx_sample_w = (tx_count_q == 32'b0);

always @ (posedge clk_i or posedge rst_i)
if (rst_i)
    tx_count_q      <= 32'b0;
else
begin
    // Idle
    if (!tx_busy_q)
        tx_count_q  <= BIT_DIV;
    // Tx bit timer
    else if (tx_count_q != 0)
        tx_count_q  <= (tx_count_q - 1);
    else if (tx_sample_w)
        tx_count_q  <= BIT_DIV;
end

//-----------------------------------------------------------------
// TX Shift Register
//-----------------------------------------------------------------
reg tx_complete_q;

always @ (posedge clk_i or posedge rst_i)
if (rst_i)
begin
    tx_shift_reg_q <= 8'h00;
    tx_busy_q      <= 1'b0;
    tx_complete_q  <= 1'b0;
end
// Tx busy
else if (tx_busy_q)
begin
    // Shift tx data
    if (tx_bits_q != START_BIT && tx_sample_w)
        tx_shift_reg_q <= {1'b0, tx_shift_reg_q[7:1]};

    // Last bit?
    if (tx_bits_q == STOP_BIT0 && tx_sample_w && !STOP_BITS)
    begin
        tx_busy_q      <= 1'b0;
        tx_complete_q  <= 1'b1;
    end
    else if (tx_bits_q == STOP_BIT1 && tx_sample_w && STOP_BITS)
    begin
        tx_busy_q      <= 1'b0;
        tx_complete_q  <= 1'b1;
    end
end
// Buffer data to transmit
else if (rx_valid_w)
begin
    tx_shift_reg_q <= rx_data_w;
    tx_busy_q      <= 1'b1;
    tx_complete_q  <= 1'b0;
end
else
    tx_complete_q  <= 1'b0;

assign rx_accept_w = ~tx_busy_q;

always @ (posedge clk_i or posedge rst_i)
if (rst_i)
    tx_bits_q  <= 4'd0;
else if (tx_sample_w && tx_busy_q)
begin
    if ((tx_bits_q == STOP_BIT1 && STOP_BITS) || (tx_bits_q == STOP_BIT0 && !STOP_BITS))
        tx_bits_q <= START_BIT;
    else
        tx_bits_q <= tx_bits_q + 4'd1;
end

//-----------------------------------------------------------------
// UART Tx Pin
//-----------------------------------------------------------------
reg txd_r;

always @ *
begin
    txd_r = 1'b1;

    if (tx_busy_q)
    begin
        // Start bit (TXD = L)
        if (tx_bits_q == START_BIT)
            txd_r = 1'b0;
        // Stop bits (TXD = H)
        else if (tx_bits_q == STOP_BIT0 || tx_bits_q == STOP_BIT1)
            txd_r = 1'b1;
        // Data bits
        else
            txd_r = tx_shift_reg_q[0];
    end
end

always @ (posedge clk_i or posedge rst_i)
if (rst_i)
    txd_q <= 1'b1;
else
    txd_q <= txd_r;

assign rx_o = txd_q;
assign rx_break_o = usb_rx_break_w;

endmodule

module usb_cdc_fifo
//-----------------------------------------------------------------
// Params
//-----------------------------------------------------------------
#(
    parameter WIDTH   = 8,
    parameter DEPTH   = 4,
    parameter ADDR_W  = 2
)
//-----------------------------------------------------------------
// Ports
//-----------------------------------------------------------------
(
    // Inputs
     input               clk_i
    ,input               rst_i
    ,input  [WIDTH-1:0]  data_in_i
    ,input               push_i
    ,input               pop_i

    // Outputs
    ,output [WIDTH-1:0]  data_out_o
    ,output              accept_o
    ,output              valid_o
);

//-----------------------------------------------------------------
// Local Params
//-----------------------------------------------------------------
localparam COUNT_W = ADDR_W + 1;

//-----------------------------------------------------------------
// Registers
//-----------------------------------------------------------------
reg [WIDTH-1:0]   ram_q[DEPTH-1:0];
reg [ADDR_W-1:0]  rd_ptr_q;
reg [ADDR_W-1:0]  wr_ptr_q;
reg [COUNT_W-1:0] count_q;

//-----------------------------------------------------------------
// Sequential
//-----------------------------------------------------------------
always @ (posedge clk_i )
if (rst_i)
begin
    count_q   <= {(COUNT_W) {1'b0}};
    rd_ptr_q  <= {(ADDR_W) {1'b0}};
    wr_ptr_q  <= {(ADDR_W) {1'b0}};
end
else
begin
    // Push
    if (push_i & accept_o)
    begin
        ram_q[wr_ptr_q] <= data_in_i;
        wr_ptr_q        <= wr_ptr_q + 1;
    end

    // Pop
    if (pop_i & valid_o)
        rd_ptr_q      <= rd_ptr_q + 1;

    // Count up
    if ((push_i & accept_o) & ~(pop_i & valid_o))
        count_q <= count_q + 1;
    // Count down
    else if (~(push_i & accept_o) & (pop_i & valid_o))
        count_q <= count_q - 1;
end

//-------------------------------------------------------------------
// Combinatorial
//-------------------------------------------------------------------
/* verilator lint_off WIDTH */
assign valid_o       = (count_q != 0);
assign accept_o      = (count_q != DEPTH);
/* verilator lint_on WIDTH */

assign data_out_o    = ram_q[rd_ptr_q];

endmodule