path: root/fpga/usrp3/lib/simple_gemac/mdio.v

// Define MDIO to add support for clause 22 and clause 45 MDIO interface
`define MDIO
// If WB clock is 62.5MHz and max MDC spec is 2.5MHz, then divide by 25
//`define MDC_HALF_PERIOD 13 // Closest int to 12.5
`define MDC_HALF_PERIOD 100
 
//  Registers
`define CPUREG_MDIO_DATA    8'h10
`define CPUREG_MDIO_ADDR    8'h14
`define CPUREG_MDIO_OP      8'h18
`define CPUREG_MDIO_CONTROL 8'h1c
`define CPUREG_MDIO_STATUS  8'h1c
`define CPUREG_GPIO         8'h20


module mdio
  (
   // Wishbone Bus
   input wb_clk_i, 
   input wb_rst_i, 
   input [7:0] wb_adr_i, 
   input [31:0] wb_dat_i, 
   input wb_we_i, 
   input wb_stb_i, 
   input wb_cyc_i, 
   output reg [31:0] wb_dat_o, 
   output wb_ack_o, 
   output reg wb_int_o,
   // MDIO
   output reg mdc, 
   output reg mdio_out, 
   output reg mdio_tri,
   input mdio_in
   );

  //
  // State Declarations
  //
  parameter  
    IDLE = 0,
      PREAMBLE1 = 1,
      PREAMBLE2 = 2,
      PREAMBLE3 = 3,
      PREAMBLE4 = 4,
      PREAMBLE5 = 5,
      PREAMBLE6 = 6,
      PREAMBLE7 = 7,
      PREAMBLE8 = 8,
      PREAMBLE9 = 9,
      PREAMBLE10 = 10,
      PREAMBLE11 = 11,
      PREAMBLE12 = 12,
      PREAMBLE13 = 13,
      PREAMBLE14 = 14,
      PREAMBLE15 = 15,
      PREAMBLE16 = 16,
      PREAMBLE17 = 17,
      PREAMBLE18 = 18,
      PREAMBLE19 = 19,
      PREAMBLE20 = 20,
      PREAMBLE21 = 21,
      PREAMBLE22 = 22,
      PREAMBLE23 = 23,
      PREAMBLE24 = 24,
      PREAMBLE25 = 25,
      PREAMBLE26 = 26,
      PREAMBLE27 = 27,
      PREAMBLE28 = 28,
      PREAMBLE29 = 29,
      PREAMBLE30 = 30,
      PREAMBLE31 = 31,
      PREAMBLE32 = 32,
      START1 = 33,
      C22_START2 = 34,
      C45_START2 = 35,
      OP1 = 36,
      OP2 = 37,
      PRTAD1 = 38,
      PRTAD2 = 39,
      PRTAD3 = 40,
      PRTAD4 = 41,
      PRTAD5 = 42,
      DEVAD1 = 43,
      DEVAD2 = 44,
      DEVAD3 = 45,
      DEVAD4 = 46,
      DEVAD5 = 47,
      TA1 = 48,
      TA2 = 49,
      TA3 = 50,
      READ1 = 51,
      READ2 = 52,
      READ3 = 53,
      READ4 = 54,
      READ5 = 55,
      READ6 = 56,
      READ7 = 57,
      READ8 = 58,
      READ9 = 59,
      READ10 = 60,
      READ11 = 61,
      READ12 = 62,
      READ13 = 63,
      READ14 = 64,
      READ15 = 65,
      READ16 = 66,
      WRITE1 = 67,
      WRITE2 = 68,
      WRITE3 = 69,
      WRITE4 = 70,
      WRITE5 = 71,
      WRITE6 = 72,
      WRITE7 = 73,
      WRITE8 = 74,
      WRITE9 = 75,
      WRITE10 = 76,
      WRITE11 = 77,
      WRITE12 = 78,
      WRITE13 = 79,
      WRITE14 = 80,
      WRITE15 = 81,
      WRITE16 = 82,
      C45_ADDR1 = 83,
      C45_ADDR2 = 84,
      C45_ADDR3 = 85,
      C45_ADDR4 = 86,
      C45_ADDR5 = 87,
      C45_ADDR6 = 88,
      C45_ADDR7 = 89,
      C45_ADDR8 = 90,
      C45_ADDR9 = 91,
      C45_ADDR10 = 92,
      C45_ADDR11 = 93,
      C45_ADDR12 = 94,
      C45_ADDR13 = 95,
      C45_ADDR14 = 96,
      C45_ADDR15 = 97,
      C45_ADDR16 = 98,
      PREIDLE = 99;
   
   reg 	 cpuack;
   reg [15:0] mdio_read_data;
   reg [15:0] mdio_write_data;
   reg [15:0] mdio_address;
   reg [12:0] mdio_operation;
   reg 	      mdio_control;
   reg [7:0]  mdc_clk_count;
   reg 	      mdc_falling_edge;
   reg 	      mdio_running;
   reg 	      mdio_done;
   reg [7:0]  state;

   
   assign wb_ack_o = cpuack && wb_stb_i;
   
   always @(posedge wb_clk_i or posedge wb_rst_i) begin
      
      if (wb_rst_i == 1'b1) begin
	 wb_dat_o <= 32'b0;
         wb_int_o <= 1'b0;
         cpuack <= 1'b0;

	 mdio_address <= 0;
	 mdio_operation <= 0;
	 mdio_write_data <= 0;
       	 mdio_running <= 0;
      end
      else begin
	 
	 wb_int_o <= 1'b0;
	 cpuack <= wb_cyc_i && wb_stb_i;
	 // Handshake to MDIO state machine to reset running flag in status.
	 // Wait for falling MDC edge to prevent S/W race condition occuring
	 // where done flag still asserted but running flag now cleared (repeatedly).
	 if (mdio_done && mdc_falling_edge)
	   mdio_running <= 0;

	 //
	 // Read access
	 //
	 if (wb_cyc_i && wb_stb_i && !wb_we_i) begin
	    
            case ({wb_adr_i[7:2], 2'b0})
	      
	      `CPUREG_MDIO_DATA: begin
		 wb_dat_o <= {16'b0, mdio_read_data};
	      end
	      
	      `CPUREG_MDIO_STATUS: begin
		 wb_dat_o <= {31'b0, mdio_running};
	      end

              default: begin
              end
	      
            endcase 
         end
	 
         //
         // Write access
	 //
         if (wb_cyc_i && wb_stb_i && wb_we_i) begin
	    $display("reg write @ addr %x",({wb_adr_i[7:2], 2'b0}));
	    
            case ({wb_adr_i[7:2], 2'b0})
	      
	      `CPUREG_MDIO_DATA: begin
		 mdio_write_data <= wb_dat_i[15:0];
	      end

	      `CPUREG_MDIO_ADDR: begin
		 mdio_address <= wb_dat_i[15:0];
	      end
	      
	      `CPUREG_MDIO_OP: begin
		 mdio_operation <= wb_dat_i[12:0];
	      end

	      `CPUREG_MDIO_CONTROL: begin
		 // Trigger mdio operation here. Cleared by state machine at end of bus transaction.
		 if (wb_dat_i[0])
		   mdio_running <= 1;		 
	      end

              default: begin
              end
	      
            endcase
	    
         end
	 
      end
      
   end // always @ (posedge wb_clk_i or posedge wb_rst_i)


   //
   // Produce mdc clock as a signal synchronously from Wishbone clock.
   //
   always @(posedge wb_clk_i or posedge wb_rst_i)
     if (wb_rst_i)
       begin
	  mdc_clk_count <= 1;
	  mdc <= 0;
	  mdc_falling_edge <= 0;	  
       end
     else if (mdc_clk_count == `MDC_HALF_PERIOD)
       begin
	  mdc_clk_count <= 1;
	  mdc <= ~mdc;
	  mdc_falling_edge <= mdc;	  
       end
     else
       begin
	  mdc_clk_count <= mdc_clk_count + 1;
	  mdc_falling_edge <= 0;		   
       end
   
   //
   // MDIO state machine
   //
   always @(posedge wb_clk_i or posedge wb_rst_i)
     if (wb_rst_i)
       begin
	  mdio_tri <= 1;
	  mdio_out <= 0;
	  mdio_done <= 0;
	  mdio_read_data <= 0;
	  state <= IDLE;
       end
     else if (mdc_falling_edge)
       //
       // This is the MDIO bus controller. Use falling edge of MDC.
       //      
       begin
	  // Defaults	  
	  mdio_tri <= 1;
	  mdio_out <= 0;
	  mdio_done <= 0;
	  
	  
	  case(state)
	    // IDLE.
	    // In Clause 22 & 45 the master of the MDIO bus is tristate during idle.
	    // 
	    IDLE: begin
	       mdio_tri <= 1;
	       mdio_out <= 0;
	       if (mdio_running)
		 state <= PREAMBLE1;
	    end
	    // Preamble. All MDIO transactions begin witrh 32bits of 1 bits as a preamble.
	    PREAMBLE1: begin
	       mdio_tri <= 0;
	       mdio_out <= 1;  
	       state <= PREAMBLE2;
	    end
	    PREAMBLE2: begin
	       mdio_tri <= 0;
	       mdio_out <= 1;  
	       state <= PREAMBLE3;
	    end 
	    PREAMBLE3: begin
	       mdio_tri <= 0;
	       mdio_out <= 1;  
	       state <= PREAMBLE4;
	    end 
	    PREAMBLE4: begin
	       mdio_tri <= 0;
	       mdio_out <= 1;  
	       state <= PREAMBLE5;
	    end 
	    PREAMBLE5: begin
	       mdio_tri <= 0;
	       mdio_out <= 1;  
	       state <= PREAMBLE6;
	    end
	    PREAMBLE6: begin
	       mdio_tri <= 0;
	       mdio_out <= 1;  
	       state <= PREAMBLE7;
	    end
	    PREAMBLE7: begin
	       mdio_tri <= 0;
	       mdio_out <= 1;  
	       state <= PREAMBLE8;
	    end
	    PREAMBLE8: begin
	       mdio_tri <= 0;
	       mdio_out <= 1;
	       state <= PREAMBLE9;
	    end
	    PREAMBLE9: begin
	       mdio_tri <= 0;
	       mdio_out <= 1;
	       state <= PREAMBLE10;
	    end
	    PREAMBLE10: begin
	       mdio_tri <= 0;
	       mdio_out <= 1;
	       state <= PREAMBLE11;
	    end
	    PREAMBLE11: begin
	       mdio_tri <= 0;
	       mdio_out <= 1;  
	       state <= PREAMBLE12;
	    end
	    PREAMBLE12: begin
	       mdio_tri <= 0;
	       mdio_out <= 1;  
	       state <= PREAMBLE13;
	    end 
	    PREAMBLE13: begin
	       mdio_tri <= 0;
	       mdio_out <= 1;  
	       state <= PREAMBLE14;
	    end 
	    PREAMBLE14: begin
	       mdio_tri <= 0;
	       mdio_out <= 1;  
	       state <= PREAMBLE15;
	    end 
	    PREAMBLE15: begin
	       mdio_tri <= 0;
	       mdio_out <= 1;  
	       state <= PREAMBLE16;
	    end
	    PREAMBLE16: begin
	       mdio_tri <= 0;
	       mdio_out <= 1;  
	       state <= PREAMBLE17;
	    end
	    PREAMBLE17: begin
	       mdio_tri <= 0;
	       mdio_out <= 1;  
	       state <= PREAMBLE18;
	    end
	    PREAMBLE18: begin
	       mdio_tri <= 0;
	       mdio_out <= 1;
	       state <= PREAMBLE19;
	    end
	    PREAMBLE19: begin
	       mdio_tri <= 0;
	       mdio_out <= 1;
	       state <= PREAMBLE20;
	    end
	    PREAMBLE20: begin
	       mdio_tri <= 0;
	       mdio_out <= 1;
	       state <= PREAMBLE21;
	    end
	    PREAMBLE21: begin
	       mdio_tri <= 0;
	       mdio_out <= 1;  
	       state <= PREAMBLE22;
	    end
	    PREAMBLE22: begin
	       mdio_tri <= 0;
	       mdio_out <= 1;  
	       state <= PREAMBLE23;
	    end 
	    PREAMBLE23: begin
	       mdio_tri <= 0;
	       mdio_out <= 1;  
	       state <= PREAMBLE24;
	    end 
	    PREAMBLE24: begin
	       mdio_tri <= 0;
	       mdio_out <= 1;  
	       state <= PREAMBLE25;
	    end 
	    PREAMBLE25: begin
	       mdio_tri <= 0;
	       mdio_out <= 1;  
	       state <= PREAMBLE26;
	    end
	    PREAMBLE26: begin
	       mdio_tri <= 0;
	       mdio_out <= 1;  
	       state <= PREAMBLE27;
	    end
	    PREAMBLE27: begin
	       mdio_tri <= 0;
	       mdio_out <= 1;  
	       state <= PREAMBLE28;
	    end
	    PREAMBLE28: begin
	       mdio_tri <= 0;
	       mdio_out <= 1;
	       state <= PREAMBLE29;
	    end
	    PREAMBLE29: begin
	       mdio_tri <= 0;
	       mdio_out <= 1;
	       state <= PREAMBLE30;
	    end
	    PREAMBLE30: begin
	       mdio_tri <= 0;
	       mdio_out <= 1;
	       state <= PREAMBLE31;
	    end
	    PREAMBLE31: begin
	       mdio_tri <= 0;
	       mdio_out <= 1;
	       state <= PREAMBLE32;
	    end
	    PREAMBLE32: begin
	       mdio_tri <= 0;
	       mdio_out <= 1;
	       state <= START1;
	    end
	    //
	    // Start code for Clause 22 is 01 and Clause 45 is 00
	    //
	    START1: begin
	       mdio_tri <= 0;
	       mdio_out <= 0;
	       if (mdio_operation[12])
		 // Clause 45 bit set.
		 state <= C45_START2;
	       else
		 state <= C22_START2;	       
	    end
	    //
	    // 2nd Clause 22 start bit is a 1
	    //
	    C22_START2: begin
	       mdio_tri <= 0;
	       mdio_out <= 1;
	       state <= OP1;
	    end
	    //
	    // 2nd Clause 45 start bit is a 0
	    //
	    C45_START2: begin
	       mdio_tri <= 0;
	       mdio_out <= 0;
	       state <= OP1;
	    end
	    //
	    // Both Clause 22 & 45 use 2 bits for operation and are compatable.
	    // Note we don't screen here for illegal Clause 22 ops.
	    //
	    OP1: begin
	       mdio_tri <= 0;
	       mdio_out <= mdio_operation[11];
	       state <= OP2;
	    end
	    OP2: begin
	       mdio_tri <= 0;
	       mdio_out <= mdio_operation[10];
	       state <= PRTAD1;
	    end
	    //
	    // Both Clause 22 & 45 use 2 sucsessive 5 bit fields to form a hierarchical address
	    // though it's used slightly different between the 2 standards.
	    //
	    PRTAD1: begin
	       mdio_tri <= 0;
	       mdio_out <= mdio_operation[9];
	       state <= PRTAD2;	       
	    end
	    PRTAD2: begin
	       mdio_tri <= 0;
	       mdio_out <= mdio_operation[8];
	       state <= PRTAD3;	       
	    end
	    PRTAD3: begin
	       mdio_tri <= 0;
	       mdio_out <= mdio_operation[7];
	       state <= PRTAD4;	       
	    end
	    PRTAD4: begin
	       mdio_tri <= 0;
	       mdio_out <= mdio_operation[6];
	       state <= PRTAD5;	       
	    end
	    PRTAD5: begin
	       mdio_tri <= 0;
	       mdio_out <= mdio_operation[5];
	       state <= DEVAD1;	       
	    end
	    DEVAD1: begin
	       mdio_tri <= 0;
	       mdio_out <= mdio_operation[4];
	       state <= DEVAD2;	       
	    end
	    DEVAD2: begin
	       mdio_tri <= 0;
	       mdio_out <= mdio_operation[3];
	       state <= DEVAD3;	       
	    end
	    DEVAD3: begin
	       mdio_tri <= 0;
	       mdio_out <= mdio_operation[2];
	       state <= DEVAD4;	       
	    end
	    DEVAD4: begin
	       mdio_tri <= 0;
	       mdio_out <= mdio_operation[1];
	       state <= DEVAD5;	       
	    end
	    DEVAD5: begin
	       mdio_tri <= 0;
	       mdio_out <= mdio_operation[0];
	       state <= TA1;	       
	    end
	    //
	    // Both Clause 22 & Clause 45 use the same turn around on the bus.
	    // Reads have Z as the first bit and 0 driven by the slave for the 2nd bit.
	    // Note that slaves drive the bus on the rising edge of MDC.
	    // Writes and Address cycles have 10 driven by the master.
	    //
	    TA1: begin
	    	// Clause22 write or clause45 write or address go to state TA2
	       if ((mdio_operation[12:11] == 2'b10) || (mdio_operation[12:11] == 2'b01))
		 begin
		    mdio_tri <= 0;
		    mdio_out <= 1;
		    state <= TA2;
		 end
	       else // Read
		 begin
		    mdio_tri <= 1;
		    state <= TA3;
		 end
	    end
	    TA2: begin
	       mdio_tri <= 0;
	       mdio_out <= 0;
	       if (!mdio_operation[12]) // Clause 22 Write
		 state <= WRITE1;
	       else if (mdio_operation[10]) // Clause 45 Write
		 state <= WRITE1;
	       else // Clause 45 ADDRESS
		 state <= C45_ADDR1;
	    end
	    TA3: begin
	       mdio_tri <= 1;
	       state <= READ1;
	    end
	    //
	    // Clause 22 Reads and both forms of clause 45 Reads have the same bus transaction from here out.
	    //
	    READ1: begin
	       mdio_tri <= 1;	
	       mdio_read_data[15] <= mdio_in;
	       state <= READ2;	    
	    end
	    READ2: begin
	       mdio_tri <= 1;	
	       mdio_read_data[14] <= mdio_in;
	       state <= READ3;	    
	    end
	    READ3: begin
	       mdio_tri <= 1;	
	       mdio_read_data[13] <= mdio_in;
	       state <= READ4;	    
	    end
	    READ4: begin
	       mdio_tri <= 1;	
	       mdio_read_data[12] <= mdio_in;
	       state <= READ5;	    
	    end
	    READ5: begin
	       mdio_tri <= 1;	
	       mdio_read_data[11] <= mdio_in;
	       state <= READ6;	    
	    end
	    READ6: begin
	       mdio_tri <= 1;	
	       mdio_read_data[10] <= mdio_in;
	       state <= READ7;	    
	    end
	    READ7: begin
	       mdio_tri <= 1;	
	       mdio_read_data[9] <= mdio_in;
	       state <= READ8;	    
	    end
	    READ8: begin
	       mdio_tri <= 1;	
	       mdio_read_data[8] <= mdio_in;
	       state <= READ9;	    
	    end
	    READ9: begin
	       mdio_tri <= 1;	
	       mdio_read_data[7] <= mdio_in;
	       state <= READ10;	    
	    end
	    READ10: begin
	       mdio_tri <= 1;	
	       mdio_read_data[6] <= mdio_in;
	       state <= READ11;	    
	    end
	    READ11: begin
	       mdio_tri <= 1;	
	       mdio_read_data[5] <= mdio_in;
	       state <= READ12;	    
	    end
	    READ12: begin
	       mdio_tri <= 1;	
	       mdio_read_data[4] <= mdio_in;
	       state <= READ13;	    
	    end
	    READ13: begin
	       mdio_tri <= 1;	
	       mdio_read_data[3] <= mdio_in;
	       state <= READ14;	    
	    end
	    READ14: begin
	       mdio_tri <= 1;	
	       mdio_read_data[2] <= mdio_in;
	       state <= READ15;	    
	    end
	    READ15: begin
	       mdio_tri <= 1;	
	       mdio_read_data[1] <= mdio_in;
	       state <= READ16;	    
	    end
	    READ16: begin
	       mdio_tri <= 1;	
	       mdio_read_data[0] <= mdio_in;
	       state <= PREIDLE;	 
	       mdio_done <= 1;	          
	    end	    
	    //
	    // Write 16bits of data for all types of Write.
	    //
	    WRITE1:begin
	       mdio_tri <= 0;
	       mdio_out <= mdio_write_data[15];
	       state <= WRITE2;
	    end
	    WRITE2:begin
	       mdio_tri <= 0;
	       mdio_out <= mdio_write_data[14];
	       state <= WRITE3;
	    end
	    WRITE3:begin
	       mdio_tri <= 0;
	       mdio_out <= mdio_write_data[13];
	       state <= WRITE4;
	    end
	    WRITE4:begin
	       mdio_tri <= 0;
	       mdio_out <= mdio_write_data[12];
	       state <= WRITE5;
	    end
	    WRITE5:begin
	       mdio_tri <= 0;
	       mdio_out <= mdio_write_data[11];
	       state <= WRITE6;
	    end
	    WRITE6:begin
	       mdio_tri <= 0;
	       mdio_out <= mdio_write_data[10];
	       state <= WRITE7;
	    end
	    WRITE7:begin
	       mdio_tri <= 0;
	       mdio_out <= mdio_write_data[9];
	       state <= WRITE8;
	    end
	    WRITE8:begin
	       mdio_tri <= 0;
	       mdio_out <= mdio_write_data[8];
	       state <= WRITE9;
	    end
	    WRITE9:begin
	       mdio_tri <= 0;
	       mdio_out <= mdio_write_data[7];
	       state <= WRITE10;
	    end
	    WRITE10:begin
	       mdio_tri <= 0;
	       mdio_out <= mdio_write_data[6];
	       state <= WRITE11;
	    end
	    WRITE11:begin
	       mdio_tri <= 0;
	       mdio_out <= mdio_write_data[5];
	       state <= WRITE12;
	    end
	    WRITE12:begin
	       mdio_tri <= 0;
	       mdio_out <= mdio_write_data[4];
	       state <= WRITE13;
	    end
	    WRITE13:begin
	       mdio_tri <= 0;
	       mdio_out <= mdio_write_data[3];
	       state <= WRITE14;
	    end
	    WRITE14:begin
	       mdio_tri <= 0;
	       mdio_out <= mdio_write_data[2];
	       state <= WRITE15;
	    end
	    WRITE15:begin
	       mdio_tri <= 0;
	       mdio_out <= mdio_write_data[1];
	       state <= WRITE16;
	    end
	    WRITE16:begin
	       mdio_tri <= 0;
	       mdio_out <= mdio_write_data[0];
	       state <= PREIDLE;
	       mdio_done <= 1;	       
	    end
	    //
	    // Write 16bits of address for a Clause 45 Address transaction
	    //
	    C45_ADDR1:begin
	       mdio_tri <= 0;
	       mdio_out <= mdio_address[15];
	       state <= C45_ADDR2;
	    end
	    C45_ADDR2:begin
	       mdio_tri <= 0;
	       mdio_out <= mdio_address[14];
	       state <= C45_ADDR3;
	    end
	    C45_ADDR3:begin
	       mdio_tri <= 0;
	       mdio_out <= mdio_address[13];
	       state <= C45_ADDR4;
	    end
	    C45_ADDR4:begin
	       mdio_tri <= 0;
	       mdio_out <= mdio_address[12];
	       state <= C45_ADDR5;
	    end
	    C45_ADDR5:begin
	       mdio_tri <= 0;
	       mdio_out <= mdio_address[11];
	       state <= C45_ADDR6;
	    end
	    C45_ADDR6:begin
	       mdio_tri <= 0;
	       mdio_out <= mdio_address[10];
	       state <= C45_ADDR7;
	    end
	    C45_ADDR7:begin
	       mdio_tri <= 0;
	       mdio_out <= mdio_address[9];
	       state <= C45_ADDR8;
	    end
	    C45_ADDR8:begin
	       mdio_tri <= 0;
	       mdio_out <= mdio_address[8];
	       state <= C45_ADDR9;
	    end
	    C45_ADDR9:begin
	       mdio_tri <= 0;
	       mdio_out <= mdio_address[7];
	       state <= C45_ADDR10;
	    end
	    C45_ADDR10:begin
	       mdio_tri <= 0;
	       mdio_out <= mdio_address[6];
	       state <= C45_ADDR11;
	    end
	    C45_ADDR11:begin
	       mdio_tri <= 0;
	       mdio_out <= mdio_address[5];
	       state <= C45_ADDR12;
	    end
	    C45_ADDR12:begin
	       mdio_tri <= 0;
	       mdio_out <= mdio_address[4];
	       state <= C45_ADDR13;
	    end
	    C45_ADDR13:begin
	       mdio_tri <= 0;
	       mdio_out <= mdio_address[3];
	       state <= C45_ADDR14;
	    end
	    C45_ADDR14:begin
	       mdio_tri <= 0;
	       mdio_out <= mdio_address[2];
	       state <= C45_ADDR15;
	    end
	    C45_ADDR15:begin
	       mdio_tri <= 0;
	       mdio_out <= mdio_address[1];
	       state <= C45_ADDR16;
	    end
	    C45_ADDR16:begin
	       mdio_tri <= 0;
	       mdio_out <= mdio_address[0];
	       state <= PREIDLE;
	       mdio_done <= 1;	       
	    end
	    //
	    // PREIDLE allows the mdio_running bit to reset.
	    //
	    PREIDLE: begin
	       state <= IDLE;
	    end
	  endcase // case(state)
	  
       end // if (mdc_falling_edge)

   
endmodule