//   ==================================================================
//   >>>>>>>>>>>>>>>>>>>>>>> COPYRIGHT NOTICE <<<<<<<<<<<<<<<<<<<<<<<<<
//   ------------------------------------------------------------------
//   Copyright (c) 2006-2011 by Lattice Semiconductor Corporation
//   ALL RIGHTS RESERVED 
//   ------------------------------------------------------------------
//
//   IMPORTANT: THIS FILE IS AUTO-GENERATED BY THE LATTICEMICO SYSTEM.
//
//   Permission:
//
//      Lattice Semiconductor grants permission to use this code
//      pursuant to the terms of the Lattice Semiconductor Corporation
//      Open Source License Agreement.  
//
//   Disclaimer:
//
//      Lattice Semiconductor provides no warranty regarding the use or
//      functionality of this code. It is the user's responsibility to
//      verify the user’s design for consistency and functionality through
//      the use of formal verification methods.
//
//   --------------------------------------------------------------------
//
//                  Lattice Semiconductor Corporation
//                  5555 NE Moore Court
//                  Hillsboro, OR 97214
//                  U.S.A
//
//                  TEL: 1-800-Lattice (USA and Canada)
//                         503-286-8001 (other locations)
//
//                  web: http://www.latticesemi.com/
//                  email: techsupport@latticesemi.com
//
//   --------------------------------------------------------------------
//                         FILE DETAILS
// File         : intface.v
// Title        : UART Component -- intface
// Code type    : Register Transfer Level
// Dependencies : 
// Description  :
//    <Global reset and clock>
//      reset        : Master reset
//      clk          : Master Clock
//
//    <Wishbone interface>
//      adr_i     : Address bus
//      dat_i     : Data bus input
//      dat_o     : Data but output
//      stb_i     : strobe output, used to indicate a valid data transfer cycle
//      cyc_i     : cycle signal, indicate whether a valid bus cycle is in process 
//      we_i      : write enable output, used to indicate whether the current cycle is a READ or Write
//      sel_i     : output array select signal, used to indicate where valid data is expected
//      ack_o     : acknowledge, indicate the nomal termination of a bus cycle
//      intr      : Interrupt
//      cti_i     : cycle type identifier, 
//      bte_i     : burst type extension
//          
//    <Registers>
//      rbr         : Receiver Buffer Register
//      thr         : Transmitter Holding Register
//      msr         : Modem Status Register
//      mcr         : Modem Control Register
//
//    <Rising edge of registers read/write strobes>
//      rbr_rd    : one CPU clk width pulse indicating RBR read strobe
//      thr_wr    : one CPU clk width pulse indicating THR write strobe
//      lsr_rd    : one CPU clk width pulse indicating LSR read strobe
//      msr_rd    : one CPU clk width pulse indicating MSR read strobe
//
//    <Receiver/Transmitter control>
//      databits    : "00"=5-bit, "01"=6-bit, "10"=7-bit, "11"=8-bit
//      stopbits    : "00"=1-bit, "01"=1.5-bit(5-bit data),
//                    "10"=2-bit(6,7,8-bit data)
//      parity_en     : '0'=Parity Bit Enable, '1'=Parity Bit Disable
//      parity_even   : '0'=Even Parity Selected, '1'=Odd Parity Selected
//      parity_stick  : '0'=Stick Parity Disable, '1'=Stick Parity Enable
//      tx_break      : '0'=Disable BREAK assertion, '1'=Assert BREAK
//
//    <Receiver/Transmitter status>
//      rx_rdy       : rbr data is ready to be read
//      overrun_err  : Overrun error
//      parity_err   : Parity error
//      frame_err    : Frame error
//      break_int    : BREAK interrupt
//      thre         : thr is empty
//      temt         : Both thr and TSR are empty
//
// --------------------------------------------------------------------
//
//
//
//----------------------------------------------------------------------------
//   GENERAL REGISTER:                                                      --
//------------------------                                                  --
//   =================================================================      --
//  |  ADDRESS A[2:0]   |            REGISTER             | IMPLEMENT |     --
//   =================================================================      --
//  | $000 (READ)       | RBR (RECEIVER BUFFER REGISTER)  |  Y        |     --
//   -----------------------------------------------------------------      --
//  | $000 (WRITE)      | THR (TRANSMIT HOLD REGISTER)    |  Y        |     --
//   =================================================================      --
//  | $001 (WRITE)      | IER (INTERRUPT ENABLE REGISTER) |  Y        |     --
//   =================================================================      --
//  | $010 (READ)       | IIR (INTERRUPT ID REGISTER)     |  Y        |     --
//   =================================================================      --
//  | $011 (WRITE)      | LCR (LINE CONTROL REGISTER)     |  Y        |     --
//   =================================================================      --
//  | $100 (WRITE)      | MCR (MODEM CONTROL REGISTER)    |  Y        |     --
//   =================================================================      --
//  | $101 (READ)       | LSR (LINE STATUS REGISTER)      |  Y        |     --
//   =================================================================      --
//  | $110 (READ)       | MSR (MODEM STATUS REGISTER)     |  Y        |     --
//   =================================================================      --
//  | $111 (READ/WRITE) | SCR (SCRATCHPAD REGISTER)       |  N        |     --
//   =================================================================      --
//                                                                          --
//  NOTE:  By using Lattice ISP solution, the Baud Rate can be
//         re-configured even when the device is soldered on the board.     --
//         Therefore the Baud Rate register set is omitted.                 --
//                                                                          --
//         Because each Lattice ispLSI device has a embedded UES register,  --
//         the Scratchpad register can be omitted too.                      --
//                                                                          --
//----------------------------------------------------------------------------
//  REGISTER BIT FIELDS:                                                    --
//--------------------------                                                --
//                                                                          --
//    ============================                                          --
//   | LSR (LINE STATUS REGISTER) |                                         --
//    ==============================================================        --
//   |  0    | TEMT | THRE  |  BI   |  FE   |  PE   |  OE   | RxRDY |       --
//    ==============================================================        --
//                                                                          --
//    RxRDY : RECEIVE DATA READY                                            --
//    OE    : OVERRUN ERROR                                                 --
//    PE    : PARITY ERROR                                                  --
//    FE    : FRAMING ERROR                                                 --
//    BI    : BREAK INTERRUPT                                               --
//    THRE  : TRASMITTER HOLDING REGISTER EMPTY                             --
//    TEMT  : TRASMITTER EMPTY                                              --
//                                                                          --
//                                                                          --
//    RxRDY: The data received flag is set to 1 at the successful           --
//           completion of a byte receive cycle.  It is automatically       --
//           cleared to 0 when the Rx Data Register is read.  If a new byte --
//           is received before an Rx Data Register read, the over run flag --
//           will be set to 1. If (SR) status option is set the UART will   --
//           ignore all further incoming bytes until the Rx Data Register   --
//           has been read.                                                 --
//                                                                          --
//    OE:    It indicates that the data in RBR was not read by the CPU      --
//           before the next character arrived, thereby destroying the the  --
//           previous character. The OE indicator is set to 1 upon          --
//           detection of an overrun condition and reset whenever the CPU   --
//           reads the contents of LSR                                      --
//                                                                          --
//    PE:    The parity error flag is set to 1 if an invalid parity bit is  --
//           encountered. It is automatically cleared to 0 when the CPU     --
//           reads the contents of Line Status Register.                    --
//                                                                          --
//    FE:    The framing error flag is set to 1 if an invalid stop bit is   --
//           encountered. It is automatically cleared to 0 when the CPU     --
//           reads the contents of Line Status Register.                    --
//                                                                          --
//    BI:    The start bit error flag is set to 1 if an invalid start bit   --
//           is encountered. It is automatically cleared to 0 when the CPU  --
//           reads the contents of Line Status Register.                    --
//                                                                          --
//    THRE:  The Transmit Holding Register Empty flag indicate that the     --
//           UART is ready to accept a new character for transmission. In   --
//           addition this bit cause the UART issue an interrupt to the CPU --
//           when the THRE interrupt enable is set to high                  --
//                                                                          --
//    TEMT:  The Transmitter Empty indicator is set to '1' whenever         --
//           whenever the Transmitter Holding Register and the Transmitter  --
//           Shifting Register are both empty. It is reset to '0' whenever  --
//           either the Transmitter Holding register or Transmitter Shift   --
//           Register contains a character                                  --
//                                                                          --
//    ================================                                      --
//   | LCR (LINE CONTROL REGISTER)    |                                     --
//    ===============================================================       --
//   |  DLAB |  SB   |  SP   | EPS   |  PEN  |  STB  | WLS1  | WLS0  |      --
//    ===============================================================       --
//                                                                          --
//    WLS1-WLS0:  WORD LENGTH SELECT  00 = 5 DATA BITS                      --
//                                    01 = 6 DATA BITS                      --
//                                    10 = 7 DATA BITS                      --
//                                    11 = 8 DATA BITS                      --
//                                                                          --
//    STB:  NUMBER OF STOP BITS  0 = 1 STOP BIT (DEFAULT)                   --
//                               1 = 1.5 STOP BITS (DATA LENGTH 5 BITS)     --
//                               1 = 2 STOP BITS   (DATA LENGTH 6,7,8 BITS) --
//                                                                          --
//    PEN:  PARITY ENABLE                                                   --
//    EPS:  EVEN PARITY SELECT                                              --
//    SP:   SET PARITY                                                      --
//                                  SP EPS PEN      PARITY SELECTION        --
//                                  X   X   0       NO PARITY               --
//                                  0   0   1       ODD PARITY              --
//                                  0   1   1       EVEN PARITY             --
//                                  1   0   1       FORCE PARITY "1"        --
//                                  1   1   1       FORCE PARITY "0"        --
//                                                                          --
//    SB:   SET BREAK When enable the Break control bit causes a break      --
//          condition to be transmitted (the TX output is forced to a logic --
//          0 state). This condition exits until disabled by resetting this --
//          bit to a logic 0.                                               --
//                                                                          --
//    DLAB: DIVISOR LATCH ACCESS BIT:   0 = Divisor latch disable (default) --
//                                      1 = Divisor latch enabled           --
//          Note: Because we use ISP solution to reconfigure Baud Rate,     --
//                this bit is omitted as well as the Baud Rate Register.    --
//                                                                          --
//    =============================                                         --
//   | IIR (INTERRUPT ID REGISTER) |                                        --
//    ===================================================================   --
//   |   0   |   0   |   0   |   0   | INT 2 | INT 1 | INT 0 | INT STAT  |  --
//    ===================================================================   --
//                                                                          --
//   PRIOTITY LEVEL  BIT-3  BIT-2  BIT-1  BIT-0  SOURCE OF INTERRUPT        --
//   NONE              0      0      0      1    NONE                       --
//   HIGHEST           0      1      1      0    LSR (OE/PE/FE/BI)          --
//   2nd               0      1      0      0    RxRDY (Receiver Data Ready)--
//   3rd               0      0      1      0    THRE (THR Empty)           --
//   4th               0      0      0      0    MSR (Modem Status Register)--
//                                                                          --
//      In the 16450 Mode Bit-3 is 0.                                       --
//                                                                          --
//    =================================                                     --
//   | IER (INTERRUPT ENABLE REGISTER) |                                    --
//    ===============================================================       --
//   |   0   |   0   |   0   |   0   |  MSI  |  RLSI |  THRI | RHRI  |      --
//    ===============================================================       --
//                                                                          --
//   RBRI:    Receiver Buffer Register Interrupt (1 = Enable, 0 = Disble)   --
//   THRI:    Transmitter Hold Register Interrupt (1 = Enalbe, 0 = Disble)  --
//   RLSI:    Receiver Line Status Interrupt (1 = Enalble, 0 = Disble)      --
//   MSI:     Modem Status Interrupt (1 = Enable, 0 = Disble)               --
//                                                                          --
//    =============================                                         --
//   | MSR (MODEM STATUS REGISTER) |                                        --
//    ===============================================================       --
//   |  DCD  |  RI   |  DSR  |  CTS  |  DDCD |  TERI |  DDSR |  DCTS |      --
//    ===============================================================       --
//                                                                          --
//   DCD:       Data Carrier Detect                                         --
//   RI:        Ring Indicator                                              --
//   DSR:       Data Set Ready                                              --
//   CTS:       Clear To Send                                               --
//   DDCD:      Delta Data Carrier Detect                                   --
//   TERI:      Trailing Edge Ring Indicator                                --
//   DDSR:      Delta Data Set Ready                                        --
//   DCTS:      Delta Clear to Send                                         --
//   Bit0-3 are set to '1' whenever a control input from the MODEM changes  --
//   state, and an Modem Stauts. Interrupt is generated. They are reset to  --
//   '0' whenever the CPU reads the Modem Status Register.                  --
//                                                                          --
//    ==============================                                        --
//   | MCR (MODEM CONTROL REGISTER) |                                       --
//    ===============================================================       --
//   |   0   |   0   |   0   | LOOP* | OUT2* | OUT1* |  RTS  |  DTR  |      --
//    ===============================================================       --
//                                                                          --
//   DTR:       Data Terminal Ready                                         --
//   RTS:       Request To Send                                             --
//   OUT1:      Auxiliary User-defined Output 1 (Not Implemented)           --
//   OUT2:      Auxiliary User-defined Output 2 (Not Implemented)           --
//   LOOP:      Local Loopback for diagnostic testing of the UART           --
//              (Not Implemented)                                           --
//                                                                          --
//   Note:      OUT1, OUT2 and LOOP are not implemented                     --
//                                                                          --
// =============================================================================
//                        REVISION HISTORY
// Version      : 1.0
// Changes Made : Initial Creation
//
// Version      : 7.0SP2
// Changes Made : No Change
//
// Version      : 7.1, 3.0
// Changes Made : msr_rd changed to be combinatorial logic
//                lsr_rd changed to be combinatorial logic
//                When IER is masked, should diasble the current INT
//
// Version      : 3.1
// Changes Made : Baudrate Generation is modified.
//                RX and TX path of the UART is updated to faster clock
//                16 word deep FIFO is implemented when FIFO option is
//                selected              
//
// Version      : 3.3
// Changes Made : Removed port-width mismatch for bus fifo_din_thr
//
// Version      : 3.4
// Changes Made : Added support to print characters transmitted by UART
//                when doing functional RTL simulation
//
// Version      : 3.5
// Changes Made : WISHBONE Address Bus is 3 bits and Data Bus is 8 bits or 32 
//                bits. All UART registers occupy a byte instead of 4 bytes 
//                (i.e. registers are accessible using 3 bits only instead 
//                of original 5 bits). UART LCR register has default value 
//                (8'b0000_0011).
// =============================================================================

`ifndef INTFACE_FILE
`define INTFACE_FILE
`include "../system_conf.v"
`include "txcver_fifo.v"
module intface 
  #(parameter CLK_IN_HZ = 20000000,
    parameter UART_WB_ADR_WIDTH = 4,
    parameter UART_WB_DAT_WIDTH = 8,
    parameter BAUD_RATE = 115200,
    parameter FIFO = 0,
    parameter LCR_DATA_BITS = 8,
    parameter LCR_STOP_BITS = 1,
    parameter LCR_PARITY_ENABLE = 0,
    parameter LCR_PARITY_ODD = 0,
    parameter LCR_PARITY_STICK = 0,
    parameter LCR_SET_BREAK = 0,
    parameter STDOUT_SIM = 0,
    parameter STDOUT_SIMFAST = 0) 
   (
    // system clock and reset
    input reset,
    input clk,
    
    // wishbone interface signals
    input cyc_i,
    input stb_i,
    input we_i,
    input [2:0] cti_i,
    input [1:0] bte_i,
    input [UART_WB_ADR_WIDTH-1:0] adr_i,
    input [UART_WB_DAT_WIDTH-1:0] dat_i,
    input sel_i,
    output reg ack_o,
    output [UART_WB_DAT_WIDTH-1:0] dat_o,
    
    output intr,
    
    // Registers
    input [UART_WB_DAT_WIDTH-1:0] rbr,
    input [UART_WB_DAT_WIDTH-1:0] rbr_fifo,		
    output [UART_WB_DAT_WIDTH-1:0] thr,
    // Rising edge of registers read/write strobes
    output rbr_rd,
    output reg thr_wr,
    output lsr_rd,
`ifdef MODEM
    output msr_rd,
    input [UART_WB_DAT_WIDTH-1:0] msr,
    output [1:0] mcr,
`endif
    // Receiver/Transmitter control
    output [1:0] databits,
    output [1:0] stopbits,
    output parity_en,
    output parity_even,
    output parity_stick,
    output tx_break,
    // Receiver/Transmitter status
    input rx_rdy,
    input overrun_err,
    input parity_err,
    input frame_err,
    input break_int,
    input thre,
    input temt,
    input fifo_empty,
    output fifo_empty_thr,
    input thr_rd,
    input fifo_almost_full,
    output reg [15:0] divisor
    ); 

   wire [6:0]  lcr_default;
   generate
      if (LCR_DATA_BITS == 5)
	assign lcr_default[1:0] = 2'b00;
      else if (LCR_DATA_BITS == 6)
	assign lcr_default[1:0] = 2'b01;
      else if (LCR_DATA_BITS == 7)
	assign lcr_default[1:0] = 2'b10;
      else
	assign lcr_default[1:0] = 2'b11;
   endgenerate

   generate
      if (LCR_STOP_BITS == 1)
	assign lcr_default[2] = 1'b0;
      else
	assign lcr_default[2] = 1'b1;
   endgenerate
   
   generate
      if (LCR_PARITY_ENABLE == 0)
	assign lcr_default[3] = 1'b0;
      else
	assign lcr_default[3] = 1'b1;
   endgenerate
   
   generate
      if (LCR_PARITY_ODD == 0)
	assign lcr_default[4] = 1'b1;
      else
	assign lcr_default[4] = 1'b0;
   endgenerate
   
   generate
      if (LCR_PARITY_STICK == 0)
	assign lcr_default[5] = 1'b0;
      else
	assign lcr_default[5] = 1'b1;
   endgenerate
   
   generate
      if (LCR_SET_BREAK == 0)
	assign lcr_default[6] = 1'b0;
      else
	assign lcr_default[6] = 1'b1;
   endgenerate
   
   wire [UART_WB_DAT_WIDTH-1:0] thr_fifo;
   reg [UART_WB_DAT_WIDTH-1:0]  thr_nonfifo; 	   
   reg [UART_WB_DAT_WIDTH-1:0]  data_8bit ;
   
   generate
      if (FIFO == 1)
	assign thr  = thr_fifo;
      else
	assign thr  = thr_nonfifo;
   endgenerate
   
   reg [6:0] 		   lsr;
   reg [6:0] 		   lcr;
   
   wire [3:0] 		   iir;
`ifdef MODEM
   reg [3:0] 		   ier;
`else 
   reg [2:0] 		   ier;
`endif 
   
   wire 		   rx_rdy_int;
   wire 		   thre_int;
   wire 		   dataerr_int;
   wire 		   data_err;
   
   wire 		   wr_strobe;
   wire 		   thr_wr_strobe;
   wire 		   rbr_rd_strobe;
   wire 		   iir_rd_strobe;
   reg 			   iir_rd_strobe_delay;
   wire 		   lsr_rd_strobe;
   wire 		   div_wr_strobe;
   reg 			   lsr2_r, lsr3_r, lsr4_r;
   
   wire 		   rbr_rd_fifo;	   	   
   reg 			   rbr_rd_nonfifo;
   
   generate
      if (FIFO == 1)
	assign rbr_rd  = rbr_rd_fifo;
      else
	assign rbr_rd  = rbr_rd_nonfifo;
   endgenerate

`ifdef MODEM 
   wire 		   modem_stat;
   wire 		   modem_int;
   wire 		   msr_rd_strobe;
   wire 		   msr_rd; 
   reg [1:0] 		   mcr;  
   reg 			   msr_rd_strobe_detect;
`endif
   
   // FIFO signals for FIFO mode
   wire 		   fifo_full_thr;
   wire 		   fifo_almost_full_thr;
   wire 		   fifo_almost_empty_thr;
   wire [7:0] 		   fifo_din_thr;
   reg 			   fifo_wr_thr;
   reg 			   fifo_wr_q_thr;
   wire 		   fifo_wr_pulse_thr;
   
   // UART baud 16x clock generator
   always @(posedge clk or posedge reset) begin
      if (reset)
        divisor <= ((CLK_IN_HZ)/(BAUD_RATE));
      else if (div_wr_strobe)
	if (adr_i[0])
	  divisor <= {dat_i[7:0],divisor[7:0]};
	else
          divisor <= {divisor[15:8],dat_i[7:0]};
   end
   
   // UART Registers Address Map
   parameter A_RBR = 4'b0000;
   parameter A_THR = 4'b0000;
   parameter A_IER = 4'b0001;
   parameter A_IIR = 4'b0010;
   parameter A_LCR = 4'b0011;
   parameter A_LSR = 4'b0101;
   parameter A_DIV = 3'b100 ;   
`ifdef MODEM
   parameter A_MSR = 4'b0110;
   parameter A_MCR = 4'b0100;
`endif
   
   always @(posedge clk or posedge reset)  
     begin 
	if (reset)
	  thr_wr <= 1'b0;
	else 
	  thr_wr <= thr_wr_strobe;
     end 
   
   assign lsr_rd = lsr_rd_strobe;
   
   assign rbr_rd_fifo = rbr_rd_strobe;
   
   always @(posedge clk or posedge reset)  
     begin 
	if (reset)
	  rbr_rd_nonfifo <= 1'b0;
	else 
	  rbr_rd_nonfifo <= rbr_rd_strobe;
     end 
   
`ifdef MODEM
   assign  msr_rd = msr_rd_strobe;
`endif
   
   ////////////////////////////////////////////////////////////////////////////////
   // Registers Read/Write Control Signals
   ////////////////////////////////////////////////////////////////////////////////
   generate
      if (FIFO == 1)
	assign wr_strobe = (adr_i[UART_WB_ADR_WIDTH-1:0] == A_THR) &&  cyc_i && stb_i &&  we_i && ~fifo_full_thr && ~ack_o;
      else
	assign wr_strobe = (adr_i[UART_WB_ADR_WIDTH-1:0] == A_THR) &&  cyc_i && stb_i &&  we_i;
      
      if ((STDOUT_SIMFAST == 1) && (STDOUT_SIM == 1)) begin
`ifdef SIMULATION
	 assign thr_wr_strobe = 1'b0;
`else
	 assign thr_wr_strobe = wr_strobe;
`endif
      end
      else begin
	 assign thr_wr_strobe = wr_strobe;
      end
   endgenerate
   
   generate
      if (FIFO == 1)
	assign rbr_rd_strobe = (adr_i[UART_WB_ADR_WIDTH-1:0] == A_RBR) &&  cyc_i && stb_i && ~we_i && ~fifo_empty && ~ack_o;
      else
	assign rbr_rd_strobe = (adr_i[UART_WB_ADR_WIDTH-1:0] == A_RBR) &&  cyc_i && stb_i && ~we_i;
   endgenerate
   
   generate
      if (FIFO == 1)
	assign iir_rd_strobe = (adr_i[UART_WB_ADR_WIDTH-1:0] == A_IIR) &&  cyc_i && stb_i && ~we_i && ~ack_o;  
      else 	   
	assign iir_rd_strobe = (adr_i[UART_WB_ADR_WIDTH-1:0] == A_IIR) &&  cyc_i && stb_i && ~we_i;
   endgenerate 
   
   generate
      if (FIFO == 1)
	assign lsr_rd_strobe = (adr_i[UART_WB_ADR_WIDTH-1:0] == A_LSR) &&  cyc_i && stb_i && ~we_i && ~ack_o; 
      else    	
	assign lsr_rd_strobe = (adr_i[UART_WB_ADR_WIDTH-1:0] == A_LSR) &&  cyc_i && stb_i && ~we_i;  
   endgenerate 
   
`ifdef MODEM 
   assign msr_rd_strobe = (adr_i[UART_WB_ADR_WIDTH-1:0] == A_MSR) &&  cyc_i && stb_i && ~we_i;
`endif
   
   assign div_wr_strobe = (adr_i[UART_WB_ADR_WIDTH-1:1] == A_DIV) &&  cyc_i && stb_i &&  we_i;  
   
   ////////////////////////////////////////////////////////////////////////////////
   // Registers Read/Write Operation
   ////////////////////////////////////////////////////////////////////////////////
   generate
      if (FIFO == 1) begin
	 always @(cyc_i or stb_i or we_i or adr_i or rbr_fifo or iir 
`ifdef MODEM
		  or msr
`endif 
		  or lsr)
	   begin
	      case (adr_i[UART_WB_ADR_WIDTH-1:0])
		A_RBR: data_8bit <= rbr_fifo;
`ifdef MODEM
		A_IER: data_8bit <= {4'b0000, ier};
`else
		A_IER: data_8bit <= {5'b00000, ier};
`endif
		A_IIR: data_8bit <= {4'b0000, iir};
		A_LCR: data_8bit <= {1'b1, lcr};
		A_LSR: data_8bit <= {1'b0, lsr};
`ifdef MODEM
		A_MCR: data_8bit <= {6'b000000, mcr};
		A_MSR: data_8bit <= msr;
`endif
		default: data_8bit <= 8'b11111111;
	      endcase	   
	   end
      end
      else begin 
	 // Register Read
	 always @(posedge clk or posedge reset)  begin 
	    if (reset)
	      data_8bit <= 8'b11111111;
	    else if (cyc_i && stb_i && ~we_i)
	      case (adr_i[UART_WB_ADR_WIDTH-1:0])
		A_RBR: data_8bit <= rbr;
`ifdef MODEM
		A_IER: data_8bit <= {4'b0000, ier};
`else
		A_IER: data_8bit <= {5'b00000, ier};
`endif
		A_IIR: data_8bit <= {4'b0000, iir};
		A_LCR: data_8bit <= {1'b1, lcr};
		A_LSR: data_8bit <= {1'b0, lsr};
`ifdef MODEM
		A_MCR: data_8bit <= {6'b000000, mcr};
		A_MSR: data_8bit <= msr;
`endif
		default: data_8bit <= 8'b11111111;
	      endcase
	 end
      end
   endgenerate 
   assign dat_o = data_8bit;   
   
   generate
      if (FIFO == 0)
	begin
	   always @(posedge clk or posedge reset)  begin
              if (reset) begin
		 thr_nonfifo <= 0;
`ifdef MODEM
		 ier <= 4'b0000;
		 mcr <= 2'b00;
`else
		 ier <= 3'b000;
`endif
		 lcr <= lcr_default; 
	      end 
	      else if (cyc_i && stb_i && we_i) begin
		case (adr_i[UART_WB_ADR_WIDTH-1:0])  
             	  A_THR: thr_nonfifo <= dat_i[7:0];
`ifdef MODEM
		  A_IER: ier <= dat_i[3:0];
		  A_MCR: mcr <= dat_i[1:0];
`else 
		  A_IER: ier <= dat_i[2:0];
`endif
		  A_LCR: lcr <= dat_i[6:0];
		  default: ;
		endcase
	      end
	   end
	end
      else 
	begin
	   always @(posedge clk or posedge reset)  begin
              if (reset) begin
`ifdef MODEM
		 ier <= 4'b0000;
		 mcr <= 2'b00;
`else
		 ier <= 3'b000;
`endif
		 lcr <= lcr_default; 
	      end 
	      else if (cyc_i && stb_i && we_i)
		case (adr_i[UART_WB_ADR_WIDTH-1:0])  
`ifdef MODEM
		  A_IER: ier <= dat_i[3:0];
		  A_MCR: mcr <= dat_i[1:0];
`else 
		  A_IER: ier <= dat_i[2:0];
`endif
		  A_LCR: lcr <= dat_i[6:0];
		  default: ;
		endcase
	   end
	end
   endgenerate
   
   generate
      if (FIFO == 1) begin
	 assign fifo_wr_pulse_thr = thr_wr_strobe;
	 assign fifo_din_thr      = dat_i[7:0];
	 txcver_fifo TX_FIFO
	   (
	    .Data        (fifo_din_thr),
	    .Clock       (clk),
	    .WrEn        (fifo_wr_pulse_thr),
	    .RdEn        (thr_rd),
	    .Reset       (reset),
	    .Q           (thr_fifo),
	    .Empty       (fifo_empty_thr),
	    .Full        (fifo_full_thr),
	    .AlmostEmpty (fifo_almost_empty_thr),
	    .AlmostFull  (fifo_almost_full_thr)   
	    );
      end
   endgenerate
   
   ////////////////////////////////////////////////////////////////////////////////
   //  Line Control Register
   ////////////////////////////////////////////////////////////////////////////////
   
   // databits : "00"=5-bit, "01"=6-bit, "10"=7-bit, "11"=8-bit
   assign databits = lcr[1:0];
   
   // stopbits : "00"=1-bit, "01"=1.5-bit(5-bit data), "10"=2-bit(6,7,8-bit data)
   assign stopbits = (lcr[2] == 1'b0) ? 2'b00 : (lcr[2:0] == 3'b100) ? 2'b01 : 2'b10;
   
   // parity_en : '0'=Parity Bit Enable, '1'=Parity Bit Disable
   assign parity_en = lcr[3];
   
   // parity_even : '0'=Even Parity Selected, '1'=Odd Parity Selected
   assign parity_even = lcr[4];
   
   // parity_stick : '0'=Stick Parity Disable, '1'=Stick Parity Enable
   assign parity_stick = lcr[5];
   
   // tx_break : '0'=Disable BREAK assertion, '1'=Assert BREAK
   assign tx_break = lcr[6];
   
   ////////////////////////////////////////////////////////////////////////////////
   //  Line Status Register
   ////////////////////////////////////////////////////////////////////////////////
   generate
      if (FIFO == 1) begin
	 always @(posedge clk or posedge reset)
	   if (reset)
	     lsr2_r <= 1'b0;
	   else if (parity_err)
	     lsr2_r  <= 1'b1;
	   else if (lsr_rd_strobe)
	     lsr2_r  <= 1'b0;
	 
	 always @(posedge clk or posedge reset)
	   if (reset)
	     lsr3_r <= 1'b0;
	   else if (frame_err)
	     lsr3_r  <= 1'b1;
	   else if (lsr_rd_strobe)
	     lsr3_r  <= 1'b0;
	 
	 always @(posedge clk or posedge reset)
	   if (reset)
	     lsr4_r <= 1'b0;
	   else if (break_int)
	     lsr4_r  <= 1'b1;
	   else if (lsr_rd_strobe)
	     lsr4_r  <= 1'b0;
	 
	 always @(posedge clk)
	   lsr <= {temt , thre , lsr4_r , lsr3_r , lsr2_r , overrun_err , rx_rdy};
      end
      else
	always @(temt or thre or break_int or frame_err or parity_err or overrun_err or rx_rdy)
	  lsr =  {temt , thre , break_int , frame_err , parity_err , overrun_err , rx_rdy};
   endgenerate
   
   ////////////////////////////////////////////////////////////////////////////////
   // Interrupt Arbitrator
   ////////////////////////////////////////////////////////////////////////////////
   
   // Int is the common interrupt line for all internal UART events
`ifdef MODEM
   assign intr = rx_rdy_int | thre_int | dataerr_int | modem_int;
`else
   assign intr = rx_rdy_int | thre_int | dataerr_int;
`endif
   
   // Receiving Data Error Flags including Overrun, Parity, Framing and Break
   generate
      if (FIFO == 1)
	assign data_err = overrun_err | lsr2_r | lsr3_r | lsr4_r;
      else	   
	assign data_err = overrun_err | parity_err | frame_err | break_int;
   endgenerate
   
   // Whenever bit0, 1, 2,or 3 is set to '1', A_WB Modem Status Interrupt is generated
`ifdef MODEM
   assign modem_stat = msr[0] | msr[1] | msr[2] | msr[3];
`endif
   
   generate
      if (FIFO == 1)
	always @(posedge clk or posedge reset)
	  if (reset)
	    iir_rd_strobe_delay <= 1'b0;
	  else
	    iir_rd_strobe_delay <= iir_rd_strobe;
   endgenerate
   
   // State Machine Definition
   parameter  idle = 3'b000;
   parameter  int0 = 3'b001;
   parameter  int1 = 3'b010;
   parameter  int2 = 3'b011;
   parameter  int3 = 3'b100;
   reg [2:0]  cs_state;

   generate 
      if (FIFO == 1) begin
	 always @(posedge clk or posedge reset) begin
            if (reset)
              cs_state <= idle;
            else
              case (cs_state)
		idle: begin
		   if (ier[2] == 1'b1 && data_err == 1'b1 )
                     cs_state <= int0;
		   else if (ier[0] == 1'b1 && (fifo_almost_full || !fifo_empty) )	       
                     cs_state <= int1;
		   else if (ier[1] == 1'b1 && thre == 1'b1)
                     cs_state <= int2;
`ifdef MODEM
		   else if (ier[3] == 1'b1 && modem_stat == 1'b1)
                     cs_state <= int3;
`endif
		end
		int0: begin
		   if ((lsr_rd_strobe == 1'b1) || (ier[2] == 1'b0)) begin    
		      if (ier[0] == 1'b1 && fifo_almost_full) 
			cs_state <= int1;
                      else	      
			cs_state <= idle; end
		end
		int1: begin
		   if (data_err == 1'b1 && ier[2] == 1'b1)
		     cs_state <= int0;     
		   else if (!fifo_almost_full || (ier[0] == 1'b0))	     	       
	             cs_state <= idle;
		end
		int2: begin
		   if (iir_rd_strobe_delay || (thre == 1'b0) || (ier[1] == 1'b0))  	       
                     cs_state <= idle;
		end
`ifdef MODEM
		int3: begin
		   if ((msr_rd_strobe)|| (ier[3] == 1'b0))
                     cs_state <= idle;
		end
`endif
		default: cs_state <= idle;
              endcase
	 end 
      end
      else  begin
	 
	 always @(posedge clk or posedge reset) begin
            if (reset)
              cs_state <= idle;
            else
              case (cs_state)
		idle: begin
		   if (ier[2] == 1'b1 && data_err == 1'b1)
                     cs_state <= int0;
		   else if (ier[0] == 1'b1 && rx_rdy == 1'b1)       	       
                     cs_state <= int1;
		   else if (ier[1] == 1'b1 && thre == 1'b1)
                     cs_state <= int2;
`ifdef MODEM
		   else if (ier[3] == 1'b1 && modem_stat == 1'b1)
                     cs_state <= int3;
`endif
		end
		int0: begin
		   if ((lsr_rd_strobe == 1'b1) || (ier[2] == 1'b0)) begin	      
		      if (ier[0] == 1'b1 && rx_rdy) 
			cs_state <= int1;
                      else	      
			cs_state <= idle; end
		end
		int1: begin
		   if (data_err == 1'b1 && ier[2] == 1'b1)
		     cs_state <= int0;     
		   else if ((rx_rdy == 1'b0) || (ier[0] == 1'b0)) 	       
	             cs_state <= idle;
		end
		int2: begin 	       
		   if (iir_rd_strobe || (thre == 1'b0) || (ier[1] == 1'b0))	       
                     cs_state <= idle;
		end
`ifdef MODEM
		int3: begin
		   if ((msr_rd_strobe)|| (ier[3] == 1'b0))
                     cs_state <= idle;
		end
`endif
		default: cs_state <= idle;
              endcase
	 end
      end
   endgenerate
   
   // ACK signal generate
   always @(posedge clk or posedge reset) begin
      if (reset)
	ack_o <= 1'b0;
      else if (ack_o)
	ack_o <= 1'b0;
      else if (cyc_i & stb_i) 
	ack_o <= 1'b1;
   end
   
   // Set Receiver Line Status Interrupt
   assign dataerr_int = (cs_state == int0) ? 1'b1 : 1'b0;
   
   // Set Received Data Available Interrupt
   assign rx_rdy_int  = (cs_state == int1) ? 1'b1 : 1'b0;
   
   // Set thr Empty Interrupt
   assign thre_int    = (cs_state == int2) ? 1'b1 : 1'b0;
   
   // Set MODEM Status Interrupt
`ifdef MODEM
   assign modem_int   = (cs_state == int3) ? 1'b1 : 1'b0;
`endif
   
   // Update IIR
   assign iir = (cs_state == int0) ? 4'b0110 :
                (cs_state == int1) ? 4'b0100 :
                (cs_state == int2) ? 4'b0010 :
                 `ifdef MODEM
                (cs_state == int3) ? 4'b0000 :
                 `endif
                4'b0001 ;  // No Interrupt Pending
   
   // synthesis translate_off
   parameter	lb_size = 256;
   generate
      if (STDOUT_SIM == 1)
      begin
	 integer	lb[(lb_size-1):0];
	 integer	lb_index;
	 integer	display_character;
	 integer	total_characters;
	 
	 initial 
	 begin
	    for (lb_index = 0; lb_index < lb_size; lb_index = lb_index + 1) 
	      lb[lb_index] = 0;
	    
	    lb_index	= lb_size - 1;
	    total_characters	= 0;
	 end
	 
	 always @(negedge clk)
	   if ((reset == 1'b0) && wr_strobe && (ack_o == 1'b0))
	     case (dat_i[7:0])
	       10, 13: // Dump the Line Buffer when we receive a Carriage Return or Line Feed
		 begin
		    lb[lb_index] = "\n";
		    total_characters = (lb_size - 1) - (lb_index - 1);
		    for (lb_index = lb_size - 1; lb_index > ((lb_size - 1) - total_characters); lb_index = lb_index - 1) 
		      begin
			 display_character = lb[lb_index];
			 $write("%s", display_character);
		      end
		    
		    for (lb_index = 0; lb_index < lb_size; lb_index = lb_index + 1) 
		      lb[lb_index] = 0;
		    
		    lb_index = lb_size - 1;
		    total_characters = 0;
		 end
	       
	       default: // All other characters are just added to the Line Buffer.
		 begin
		    lb[lb_index] = dat_i[7:0];
		    lb_index = lb_index - 1;
		    total_characters = total_characters + 1;
		    
		    // Dump the Line Buffer when it is full
		    if (total_characters == (lb_size - 1))
		      begin
			 for (lb_index = lb_size - 1; lb_index >= 0; lb_index = lb_index - 1) 
			   begin
			      display_character = lb[lb_index];
			      $write("%s", display_character);
			   end
			 
			 for (lb_index = 0; lb_index < lb_size; lb_index = lb_index + 1) 
			   lb[lb_index] = 0;
			 
			 lb_index = lb_size - 1;
			 total_characters = 0;
		      end
		 end
	     endcase
      end
   endgenerate
   // synthesis translate_on
   
endmodule
`endif // INTFACE_FILE