module axi4lite_slave #
    (
        // Users to add parameters here
        
        // User parameters ends
        // Do not modify the parameters beyond this line

        // Width of S_AXI data bus
        parameter integer AXIS_DATA_WIDTH    = 32,
        // Width of S_AXI address bus
        parameter integer AXIS_ADDR_WIDTH    = 32
    )
    (
        // Users to add ports here
        input  wire [AXIS_DATA_WIDTH-1:0] slv_reg0_in,
        output reg  [AXIS_DATA_WIDTH-1:0] slv_reg0_out,

        input  wire [AXIS_DATA_WIDTH-1:0] slv_reg1_in,
        output reg  [AXIS_DATA_WIDTH-1:0] slv_reg1_out,

        input  wire [AXIS_DATA_WIDTH-1:0] slv_reg2_in,
        output reg  [AXIS_DATA_WIDTH-1:0] slv_reg2_out,

        input  wire [AXIS_DATA_WIDTH-1:0] slv_reg3_in,
        output reg  [AXIS_DATA_WIDTH-1:0] slv_reg3_out,

        input  wire [AXIS_DATA_WIDTH-1:0] slv_reg4_in,
        output reg  [AXIS_DATA_WIDTH-1:0] slv_reg4_out,

        input  wire [AXIS_DATA_WIDTH-1:0] slv_reg5_in,
        output reg  [AXIS_DATA_WIDTH-1:0] slv_reg5_out,

        input  wire [AXIS_DATA_WIDTH-1:0] slv_reg6_in,
        output reg  [AXIS_DATA_WIDTH-1:0] slv_reg6_out,

        input  wire [AXIS_DATA_WIDTH-1:0] slv_reg7_in,
        output reg  [AXIS_DATA_WIDTH-1:0] slv_reg7_out,

        input  wire [AXIS_DATA_WIDTH-1:0] slv_reg8_in,
        output reg  [AXIS_DATA_WIDTH-1:0] slv_reg8_out,

        input  wire [AXIS_DATA_WIDTH-1:0] slv_reg9_in,
        output reg  [AXIS_DATA_WIDTH-1:0] slv_reg9_out,

        input  wire [AXIS_DATA_WIDTH-1:0] slv_reg10_in,
        output reg  [AXIS_DATA_WIDTH-1:0] slv_reg10_out,

        input  wire [AXIS_DATA_WIDTH-1:0] slv_reg11_in,
        output reg  [AXIS_DATA_WIDTH-1:0] slv_reg11_out,

        input  wire [AXIS_DATA_WIDTH-1:0] slv_reg12_in,
        output reg  [AXIS_DATA_WIDTH-1:0] slv_reg12_out,

        input  wire [AXIS_DATA_WIDTH-1:0] slv_reg13_in,
        output reg  [AXIS_DATA_WIDTH-1:0] slv_reg13_out,

        input  wire [AXIS_DATA_WIDTH-1:0] slv_reg14_in,
        output reg  [AXIS_DATA_WIDTH-1:0] slv_reg14_out,

        input  wire [AXIS_DATA_WIDTH-1:0] slv_reg15_in,
        output reg  [AXIS_DATA_WIDTH-1:0] slv_reg15_out,

        // User ports ends
        // Do not modify the ports beyond this line

        // Global Clock Signal
        input wire  S_AXI_ACLK,
        // Global Reset Signal. This Signal is Active LOW
        input wire  S_AXI_ARESETN,
        // Write address (issued by master, acceped by Slave)
        input wire [AXIS_ADDR_WIDTH-1 : 0] S_AXI_AWADDR,
        // Write channel Protection type. This signal indicates the
            // privilege and security level of the transaction, and whether
            // the transaction is a data access or an instruction access.
        input wire [2 : 0] S_AXI_AWPROT,
        // Write address valid. This signal indicates that the master signaling
            // valid write address and control information.
        input wire  S_AXI_AWVALID,
        // Write address ready. This signal indicates that the slave is ready
            // to accept an address and associated control signals.
        output wire  S_AXI_AWREADY,
        // Write data (issued by master, acceped by Slave) 
        input wire [AXIS_DATA_WIDTH-1 : 0] S_AXI_WDATA,
        // Write strobes. This signal indicates which byte lanes hold
            // valid data. There is one write strobe bit for each eight
            // bits of the write data bus.    
        input wire [(AXIS_DATA_WIDTH/8)-1 : 0] S_AXI_WSTRB,
        // Write valid. This signal indicates that valid write
            // data and strobes are available.
        input wire  S_AXI_WVALID,
        // Write ready. This signal indicates that the slave
            // can accept the write data.
        output wire  S_AXI_WREADY,
        // Write response. This signal indicates the status
            // of the write transaction.
        output wire [1 : 0] S_AXI_BRESP,
        // Write response valid. This signal indicates that the channel
            // is signaling a valid write response.
        output wire  S_AXI_BVALID,
        // Response ready. This signal indicates that the master
            // can accept a write response.
        input wire  S_AXI_BREADY,
        // Read address (issued by master, acceped by Slave)
        input wire [AXIS_ADDR_WIDTH-1 : 0] S_AXI_ARADDR,
        // Protection type. This signal indicates the privilege
            // and security level of the transaction, and whether the
            // transaction is a data access or an instruction access.
        input wire [2 : 0] S_AXI_ARPROT,
        // Read address valid. This signal indicates that the channel
            // is signaling valid read address and control information.
        input wire  S_AXI_ARVALID,
        // Read address ready. This signal indicates that the slave is
            // ready to accept an address and associated control signals.
        output wire  S_AXI_ARREADY,
        // Read data (issued by slave)
        output wire [AXIS_DATA_WIDTH-1 : 0] S_AXI_RDATA,
        // Read response. This signal indicates the status of the
            // read transfer.
        output wire [1 : 0] S_AXI_RRESP,
        // Read valid. This signal indicates that the channel is
            // signaling the required read data.
        output wire  S_AXI_RVALID,
        // Read ready. This signal indicates that the master can
            // accept the read data and response information.
        input wire  S_AXI_RREADY
    );

    // AXI4LITE signals
    reg [AXIS_ADDR_WIDTH-1 : 0]     axi_awaddr;
    reg      axi_awready;
    reg      axi_wready;
    reg [1 : 0]     axi_bresp;
    reg      axi_bvalid;
    reg [AXIS_ADDR_WIDTH-1 : 0]     axi_araddr;
    reg      axi_arready;
    reg [AXIS_DATA_WIDTH-1 : 0]     axi_rdata;
    reg [1 : 0]     axi_rresp;
    reg      axi_rvalid;


    reg [AXIS_DATA_WIDTH-1:0]    slv_reg0_d;

    // Example-specific design signals
    // local parameter for addressing 32 bit / 64 bit AXIS_DATA_WIDTH
    // ADDR_LSB is used for addressing 32/64 bit registers/memories
    // ADDR_LSB = 2 for 32 bits (n downto 2)
    // ADDR_LSB = 3 for 64 bits (n downto 3)
    localparam integer ADDR_LSB = (AXIS_DATA_WIDTH/32) + 1;
    localparam integer OPT_MEM_ADDR_BITS = 4;
    //----------------------------------------------
    //-- Signals for user logic register space example
    //------------------------------------------------
    //-- Number of Slave Registers 8
    //reg [AXIS_DATA_WIDTH-1:0]    slv_reg0;
    //reg [AXIS_DATA_WIDTH-1:0]    slv_reg1;
    //reg [AXIS_DATA_WIDTH-1:0]    slv_reg2;
    //reg [AXIS_DATA_WIDTH-1:0]    slv_reg3;
    //reg [AXIS_DATA_WIDTH-1:0]    slv_reg4;
    //reg [AXIS_DATA_WIDTH-1:0]    slv_reg5;
    //reg [AXIS_DATA_WIDTH-1:0]    slv_reg6;
    //reg [AXIS_DATA_WIDTH-1:0]    slv_reg7;
    wire     slv_reg_rden;
    wire     slv_reg_wren;
    reg [AXIS_DATA_WIDTH-1:0]     reg_data_out;
    integer     byte_index;

    // Invoke the accelerator
    //reg [AXIS_DATA_WIDTH-1:0]    num_transactions;
//    reg     num_transactions;
    // I/O Connections assignments

    assign S_AXI_AWREADY    = axi_awready;
    assign S_AXI_WREADY    = axi_wready;
    assign S_AXI_BRESP    = axi_bresp;
    assign S_AXI_BVALID    = axi_bvalid;
    assign S_AXI_ARREADY    = axi_arready;
    assign S_AXI_RDATA    = axi_rdata;
    assign S_AXI_RRESP    = axi_rresp;
    assign S_AXI_RVALID    = axi_rvalid;
    // Implement axi_awready generation
    // axi_awready is asserted for one S_AXI_ACLK clock cycle when both
    // S_AXI_AWVALID and S_AXI_WVALID are asserted. axi_awready is
    // de-asserted when reset is low.

    always @( posedge S_AXI_ACLK )
    begin
      if ( S_AXI_ARESETN == 1'b0 )
        begin
          axi_awready <= 1'b0;
        end 
      else
        begin    
          if (~axi_awready && S_AXI_AWVALID && S_AXI_WVALID)
            begin
              // slave is ready to accept write address when 
              // there is a valid write address and write data
              // on the write address and data bus. This design 
              // expects no outstanding transactions. 
              axi_awready <= 1'b1;
            end
          else           
            begin
              axi_awready <= 1'b0;
            end
        end 
    end       

    // Implement axi_awaddr latching
    // This process is used to latch the address when both 
    // S_AXI_AWVALID and S_AXI_WVALID are valid. 

    always @( posedge S_AXI_ACLK )
    begin
      if ( S_AXI_ARESETN == 1'b0 )
        begin
          axi_awaddr <= 0;
        end 
      else
        begin    
          if (~axi_awready && S_AXI_AWVALID && S_AXI_WVALID)
            begin
              // Write Address latching 
              axi_awaddr <= S_AXI_AWADDR;
            end
        end 
    end       

    // Implement axi_wready generation
    // axi_wready is asserted for one S_AXI_ACLK clock cycle when both
    // S_AXI_AWVALID and S_AXI_WVALID are asserted. axi_wready is 
    // de-asserted when reset is low. 

    always @( posedge S_AXI_ACLK )
    begin
      if ( S_AXI_ARESETN == 1'b0 )
        begin
          axi_wready <= 1'b0;
        end 
      else
        begin    
          if (~axi_wready && S_AXI_WVALID && S_AXI_AWVALID)
            begin
              // slave is ready to accept write data when 
              // there is a valid write address and write data
              // on the write address and data bus. This design 
              // expects no outstanding transactions. 
              axi_wready <= 1'b1;
            end
          else
            begin
              axi_wready <= 1'b0;
            end
        end 
    end       

    // Implement memory mapped register select and write logic generation
    // The write data is accepted and written to memory mapped registers when
    // axi_awready, S_AXI_WVALID, axi_wready and S_AXI_WVALID are asserted. Write strobes are used to
    // select byte enables of slave registers while writing.
    // These registers are cleared when reset (active low) is applied.
    // Slave register write enable is asserted when valid address and data are available
    // and the slave is ready to accept the write address and write data.
    assign slv_reg_wren = axi_wready && S_AXI_WVALID && axi_awready && S_AXI_AWVALID;

    always @( posedge S_AXI_ACLK )
    begin
      if ( S_AXI_ARESETN == 1'b0 )
        begin
          slv_reg0_out <= 0;
          slv_reg1_out <= 0;
          slv_reg2_out <= 0;
          slv_reg3_out <= 0;
          slv_reg4_out <= 0;
          slv_reg5_out <= 0;
          slv_reg6_out <= 0;
          slv_reg7_out <= 0;
        end 
      else begin
        if (slv_reg_wren)
          begin
            case ( axi_awaddr[ADDR_LSB+OPT_MEM_ADDR_BITS:ADDR_LSB] )
              4'd0:
                for ( byte_index = 0; byte_index <= (AXIS_DATA_WIDTH/8)-1; byte_index = byte_index+1 )
                  if ( S_AXI_WSTRB[byte_index] == 1 ) begin
                    // Respective byte enables are asserted as per write strobes 
                    // Slave register 0
                    slv_reg0_out[(byte_index*8) +: 8] <= S_AXI_WDATA[(byte_index*8) +: 8];
                  end  
              4'd1:
                for ( byte_index = 0; byte_index <= (AXIS_DATA_WIDTH/8)-1; byte_index = byte_index+1 )
                  if ( S_AXI_WSTRB[byte_index] == 1 ) begin
                    // Respective byte enables are asserted as per write strobes 
                    // Slave register 1
                    slv_reg1_out[(byte_index*8) +: 8] <= S_AXI_WDATA[(byte_index*8) +: 8];
                  end  
              4'd2:
                for ( byte_index = 0; byte_index <= (AXIS_DATA_WIDTH/8)-1; byte_index = byte_index+1 )
                  if ( S_AXI_WSTRB[byte_index] == 1 ) begin
                    // Respective byte enables are asserted as per write strobes 
                    // Slave register 2
                    slv_reg2_out[(byte_index*8) +: 8] <= S_AXI_WDATA[(byte_index*8) +: 8];
                  end  
              4'd3:
                for ( byte_index = 0; byte_index <= (AXIS_DATA_WIDTH/8)-1; byte_index = byte_index+1 )
                  if ( S_AXI_WSTRB[byte_index] == 1 ) begin
                    // Respective byte enables are asserted as per write strobes 
                    // Slave register 3
                    slv_reg3_out[(byte_index*8) +: 8] <= S_AXI_WDATA[(byte_index*8) +: 8];
                  end  
              4'd4:
                for ( byte_index = 0; byte_index <= (AXIS_DATA_WIDTH/8)-1; byte_index = byte_index+1 )
                  if ( S_AXI_WSTRB[byte_index] == 1 ) begin
                    // Respective byte enables are asserted as per write strobes 
                    // Slave register 4
                    slv_reg4_out[(byte_index*8) +: 8] <= S_AXI_WDATA[(byte_index*8) +: 8];
                  end  
              4'd5:
                for ( byte_index = 0; byte_index <= (AXIS_DATA_WIDTH/8)-1; byte_index = byte_index+1 )
                  if ( S_AXI_WSTRB[byte_index] == 1 ) begin
                    // Respective byte enables are asserted as per write strobes 
                    // Slave register 5
                    slv_reg5_out[(byte_index*8) +: 8] <= S_AXI_WDATA[(byte_index*8) +: 8];
                  end  
              4'd6:
                for ( byte_index = 0; byte_index <= (AXIS_DATA_WIDTH/8)-1; byte_index = byte_index+1 )
                  if ( S_AXI_WSTRB[byte_index] == 1 ) begin
                    // Respective byte enables are asserted as per write strobes 
                    // Slave register 6
                    slv_reg6_out[(byte_index*8) +: 8] <= S_AXI_WDATA[(byte_index*8) +: 8];
                  end  
              4'd7:
                for ( byte_index = 0; byte_index <= (AXIS_DATA_WIDTH/8)-1; byte_index = byte_index+1 )
                  if ( S_AXI_WSTRB[byte_index] == 1 ) begin
                    // Respective byte enables are asserted as per write strobes 
                    // Slave register 7
                    slv_reg7_out[(byte_index*8) +: 8] <= S_AXI_WDATA[(byte_index*8) +: 8];
                  end  
              4'd8:
                for ( byte_index = 0; byte_index <= (AXIS_DATA_WIDTH/8)-1; byte_index = byte_index+1 )
                  if ( S_AXI_WSTRB[byte_index] == 1 ) begin
                    // Respective byte enables are asserted as per write strobes 
                    // Slave register 0
                    slv_reg8_out[(byte_index*8) +: 8] <= S_AXI_WDATA[(byte_index*8) +: 8];
                  end  
              4'd9:
                for ( byte_index = 0; byte_index <= (AXIS_DATA_WIDTH/8)-1; byte_index = byte_index+1 )
                  if ( S_AXI_WSTRB[byte_index] == 1 ) begin
                    // Respective byte enables are asserted as per write strobes 
                    // Slave register 1
                    slv_reg9_out[(byte_index*8) +: 8] <= S_AXI_WDATA[(byte_index*8) +: 8];
                  end  
              4'd10:
                for ( byte_index = 0; byte_index <= (AXIS_DATA_WIDTH/8)-1; byte_index = byte_index+1 )
                  if ( S_AXI_WSTRB[byte_index] == 1 ) begin
                    // Respective byte enables are asserted as per write strobes 
                    // Slave register 2
                    slv_reg10_out[(byte_index*8) +: 8] <= S_AXI_WDATA[(byte_index*8) +: 8];
                  end  
              4'd11:
                for ( byte_index = 0; byte_index <= (AXIS_DATA_WIDTH/8)-1; byte_index = byte_index+1 )
                  if ( S_AXI_WSTRB[byte_index] == 1 ) begin
                    // Respective byte enables are asserted as per write strobes 
                    // Slave register 3
                    slv_reg11_out[(byte_index*8) +: 8] <= S_AXI_WDATA[(byte_index*8) +: 8];
                  end  
              4'd12:
                for ( byte_index = 0; byte_index <= (AXIS_DATA_WIDTH/8)-1; byte_index = byte_index+1 )
                  if ( S_AXI_WSTRB[byte_index] == 1 ) begin
                    // Respective byte enables are asserted as per write strobes 
                    // Slave register 4
                    slv_reg12_out[(byte_index*8) +: 8] <= S_AXI_WDATA[(byte_index*8) +: 8];
                  end  
              4'd13:
                for ( byte_index = 0; byte_index <= (AXIS_DATA_WIDTH/8)-1; byte_index = byte_index+1 )
                  if ( S_AXI_WSTRB[byte_index] == 1 ) begin
                    // Respective byte enables are asserted as per write strobes 
                    // Slave register 5
                    slv_reg13_out[(byte_index*8) +: 8] <= S_AXI_WDATA[(byte_index*8) +: 8];
                  end  
              4'd14:
                for ( byte_index = 0; byte_index <= (AXIS_DATA_WIDTH/8)-1; byte_index = byte_index+1 )
                  if ( S_AXI_WSTRB[byte_index] == 1 ) begin
                    // Respective byte enables are asserted as per write strobes 
                    // Slave register 6
                    slv_reg14_out[(byte_index*8) +: 8] <= S_AXI_WDATA[(byte_index*8) +: 8];
                  end  
              4'd15:
                for ( byte_index = 0; byte_index <= (AXIS_DATA_WIDTH/8)-1; byte_index = byte_index+1 )
                  if ( S_AXI_WSTRB[byte_index] == 1 ) begin
                    // Respective byte enables are asserted as per write strobes 
                    // Slave register 7
                    slv_reg15_out[(byte_index*8) +: 8] <= S_AXI_WDATA[(byte_index*8) +: 8];
                  end  
              default : begin
                          slv_reg0_out <= slv_reg0_out;
                          slv_reg1_out <= slv_reg1_out;
                          slv_reg2_out <= slv_reg2_out;
                          slv_reg3_out <= slv_reg3_out;
                          slv_reg4_out <= slv_reg4_out;
                          slv_reg5_out <= slv_reg5_out;
                          slv_reg6_out <= slv_reg6_out;
                          slv_reg7_out <= slv_reg7_out;
                        end
            endcase
          end
      end
    end    

    // Implement write response logic generation
    // The write response and response valid signals are asserted by the slave 
    // when axi_wready, S_AXI_WVALID, axi_wready and S_AXI_WVALID are asserted.  
    // This marks the acceptance of address and indicates the status of 
    // write transaction.

    always @( posedge S_AXI_ACLK )
    begin
      if ( S_AXI_ARESETN == 1'b0 )
        begin
          axi_bvalid  <= 0;
          axi_bresp   <= 2'b0;
        end 
      else
        begin    
          if (axi_awready && S_AXI_AWVALID && ~axi_bvalid && axi_wready && S_AXI_WVALID)
            begin
              // indicates a valid write response is available
              axi_bvalid <= 1'b1;
              axi_bresp  <= 2'b0; // 'OKAY' response 
            end                   // work error responses in future
          else
            begin
              if (S_AXI_BREADY && axi_bvalid) 
                //check if bready is asserted while bvalid is high) 
                //(there is a possibility that bready is always asserted high)   
                begin
                  axi_bvalid <= 1'b0; 
                end  
            end
        end
    end   

    // Implement axi_arready generation
    // axi_arready is asserted for one S_AXI_ACLK clock cycle when
    // S_AXI_ARVALID is asserted. axi_awready is 
    // de-asserted when reset (active low) is asserted. 
    // The read address is also latched when S_AXI_ARVALID is 
    // asserted. axi_araddr is reset to zero on reset assertion.

    always @( posedge S_AXI_ACLK )
    begin
      if ( S_AXI_ARESETN == 1'b0 )
        begin
          axi_arready <= 1'b0;
          axi_araddr  <= 32'b0;
        end 
      else
        begin    
          if (~axi_arready && S_AXI_ARVALID)
            begin
              // indicates that the slave has acceped the valid read address
              axi_arready <= 1'b1;
              // Read address latching
              axi_araddr  <= S_AXI_ARADDR;
            end
          else
            begin
              axi_arready <= 1'b0;
            end
        end 
    end       

    // Implement axi_arvalid generation
    // axi_rvalid is asserted for one S_AXI_ACLK clock cycle when both 
    // S_AXI_ARVALID and axi_arready are asserted. The slave registers 
    // data are available on the axi_rdata bus at this instance. The 
    // assertion of axi_rvalid marks the validity of read data on the 
    // bus and axi_rresp indicates the status of read transaction.axi_rvalid 
    // is deasserted on reset (active low). axi_rresp and axi_rdata are 
    // cleared to zero on reset (active low).  
    always @( posedge S_AXI_ACLK )
    begin
      if ( S_AXI_ARESETN == 1'b0 )
        begin
          axi_rvalid <= 0;
          axi_rresp  <= 0;
        end 
      else
        begin    
          if (axi_arready && S_AXI_ARVALID && ~axi_rvalid)
            begin
              // Valid read data is available at the read data bus
              axi_rvalid <= 1'b1;
              axi_rresp  <= 2'b0; // 'OKAY' response
            end   
          else if (axi_rvalid && S_AXI_RREADY)
            begin
              // Read data is accepted by the master
              axi_rvalid <= 1'b0;
            end                
        end
    end    

    // Implement memory mapped register select and read logic generation
    // Slave register read enable is asserted when valid address is available
    // and the slave is ready to accept the read address.
    assign slv_reg_rden = axi_arready & S_AXI_ARVALID & ~axi_rvalid;
    always @(*)
    begin
          // Address decoding for reading registers
          case ( axi_araddr[ADDR_LSB+OPT_MEM_ADDR_BITS:ADDR_LSB] )

            4'd0    : reg_data_out <= slv_reg0_in;
            4'd1    : reg_data_out <= slv_reg1_in;
            4'd2    : reg_data_out <= slv_reg2_in;
            4'd3    : reg_data_out <= slv_reg3_in;
            4'd4    : reg_data_out <= slv_reg4_in;
            4'd5    : reg_data_out <= slv_reg5_in;
            4'd6    : reg_data_out <= slv_reg6_in;
            4'd7    : reg_data_out <= slv_reg7_in;

            4'd8    : reg_data_out <= slv_reg8_in;
            4'd9    : reg_data_out <= slv_reg9_in;
            4'd10   : reg_data_out <= slv_reg10_in;
            4'd11   : reg_data_out <= slv_reg11_in;
            4'd12   : reg_data_out <= slv_reg12_in;
            4'd13   : reg_data_out <= slv_reg13_in;
            4'd14   : reg_data_out <= slv_reg14_in;
            4'd15   : reg_data_out <= slv_reg15_in;

            default : reg_data_out <= 32'hDEADBEEF;

          endcase
    end

    // Output register or memory read data
    always @( posedge S_AXI_ACLK )
    begin
      if ( S_AXI_ARESETN == 1'b0 )
        begin
          axi_rdata  <= 0;
        end 
      else
        begin    
          // When there is a valid read address (S_AXI_ARVALID) with 
          // acceptance of read address by the slave (axi_arready), 
          // output the read dada 
          if (slv_reg_rden)
            begin
              axi_rdata <= reg_data_out;     // register read data
            end   
        end
    end    

    endmodule