///////////////////////////////////////////////////////////////////////////////
//
// 6.111 FPGA Labkit -- Hex display driver
//
//
// File:   display_16hex.v
// Date:   24-Sep-05
//
// Created: April 27, 2004
// Author: Nathan Ickes
//
// This module drives the labkit hex displays and shows the value of 
// 8 bytes (16 hex digits) on the displays.
//
// 24-Sep-05 Ike: updated to use new reset-once state machine, remove clear
// 02-Nov-05 Ike: updated to make it completely synchronous
//
// Inputs:
//
//   reset       - active high
//   clock_27mhz - the synchronous clock
//   data        - 64 bits; each 4 bits gives a hex digit
//   
// Outputs:
//
//    disp_*     - display lines used in the 6.111 labkit (rev 003 & 004)
//
///////////////////////////////////////////////////////////////////////////////


module display_16hex (reset, clock_27mhz, data_in, 
		disp_blank, disp_clock, disp_rs, disp_ce_b,
		disp_reset_b, disp_data_out);

   input reset, clock_27mhz;    // clock and reset (active high reset)
   input [63:0] data_in;		// 16 hex nibbles to display
   
   output disp_blank, disp_clock, disp_data_out, disp_rs, disp_ce_b, 
	  disp_reset_b;
   
   reg disp_data_out, disp_rs, disp_ce_b, disp_reset_b;
   
   ////////////////////////////////////////////////////////////////////////////
   //
   // Display Clock
   //
   // Generate a 500kHz clock for driving the displays.
   //
   ////////////////////////////////////////////////////////////////////////////
   
   reg [5:0] count;
   reg [7:0] reset_count;
//   reg 	     old_clock;
   wire      dreset;
   wire      clock = (count<27) ? 0 : 1;

   always @(posedge clock_27mhz)
     begin
	count <= reset ? 0 : (count==53 ? 0 : count+1);
	reset_count <= reset ? 100 : ((reset_count==0) ? 0 : reset_count-1);
//	old_clock <= clock;
     end

   assign dreset = (reset_count != 0);
   assign disp_clock = ~clock;
   wire   clock_tick = ((count==27) ? 1 : 0);
//   wire   clock_tick = clock & ~old_clock;

   ////////////////////////////////////////////////////////////////////////////
   //
   // Display State Machine
   //
   ////////////////////////////////////////////////////////////////////////////
      
   reg [7:0] state;		// FSM state
   reg [9:0] dot_index;		// index to current dot being clocked out
   reg [31:0] control;		// control register
   reg [3:0] char_index;	// index of current character
   reg [39:0] dots;		// dots for a single digit 
   reg [3:0] nibble;		// hex nibble of current character
   reg [63:0] data;
   
   assign disp_blank = 1'b0; // low <= not blanked
   
   always @(posedge clock_27mhz)
     if (clock_tick) 
       begin
	  if (dreset)
	    begin
	       state <= 0;
	       dot_index <= 0;
	       control <= 32'h7F7F7F7F;
	    end
	  else
	    casex (state)
	      8'h00:
		begin
		   // Reset displays
		   disp_data_out <= 1'b0; 
		   disp_rs <= 1'b0; // dot register
		   disp_ce_b <= 1'b1;
		   disp_reset_b <= 1'b0;	     
		   dot_index <= 0;
		   state <= state+1;
		end
	      
	      8'h01:
		begin
		   // End reset
		   disp_reset_b <= 1'b1;
		   state <= state+1;
		end
	      
	      8'h02:
		begin
		   // Initialize dot register (set all dots to zero)
		   disp_ce_b <= 1'b0;
		   disp_data_out <= 1'b0; // dot_index[0];
		   if (dot_index == 639)
		     state <= state+1;
		   else
		     dot_index <= dot_index+1;
		end
	      
	      8'h03:
		begin
		   // Latch dot data
		   disp_ce_b <= 1'b1;
		   dot_index <= 31;		// re-purpose to init ctrl reg
		   state <= state+1;
		end
	      
	      8'h04:
		begin
		   // Setup the control register
		   disp_rs <= 1'b1; // Select the control register
		   disp_ce_b <= 1'b0;
		   disp_data_out <= control[31];
		   control <= {control[30:0], 1'b0};	// shift left
		   if (dot_index == 0)
		     state <= state+1;
		   else
		     dot_index <= dot_index-1;
		end
	      
	      8'h05:
		begin
		   // Latch the control register data / dot data
		   disp_ce_b <= 1'b1;
		   dot_index <= 39;		// init for single char
		   char_index <= 15;		// start with MS char
		   data <= data_in;
		   state <= state+1;
		end
	      
	      8'h06:
		begin
		   // Load the user's dot data into the dot reg, char by char
		   disp_rs <= 1'b0;	 		// Select the dot register
		   disp_ce_b <= 1'b0;
		   disp_data_out <= dots[dot_index]; // dot data from msb
		   if (dot_index == 0)
	             if (char_index == 0)
	               state <= 5;			// all done, latch data
		     else
		       begin
			  char_index <= char_index - 1;	// goto next char
			  data <= data_in;
			  dot_index <= 39;
		       end
		   else
		     dot_index <= dot_index-1;	// else loop thru all dots 
		end
	      
	    endcase // casex(state)
       end

   always @ (data or char_index)
     case (char_index)
       4'h0: 	 	nibble <= data[3:0];
       4'h1: 	 	nibble <= data[7:4];
       4'h2: 	 	nibble <= data[11:8];
       4'h3: 	 	nibble <= data[15:12];
       4'h4: 	 	nibble <= data[19:16];
       4'h5: 	 	nibble <= data[23:20];
       4'h6: 	 	nibble <= data[27:24];
       4'h7: 	 	nibble <= data[31:28];
       4'h8: 	 	nibble <= data[35:32];
       4'h9: 	 	nibble <= data[39:36];
       4'hA: 	 	nibble <= data[43:40];
       4'hB: 	 	nibble <= data[47:44];
       4'hC: 	 	nibble <= data[51:48];
       4'hD: 	 	nibble <= data[55:52];
       4'hE: 	 	nibble <= data[59:56];
       4'hF: 	 	nibble <= data[63:60];
     endcase
      
   always @(nibble)
     case (nibble)
       4'h0: dots <= 40'b00111110_01010001_01001001_01000101_00111110;
       4'h1: dots <= 40'b00000000_01000010_01111111_01000000_00000000;
       4'h2: dots <= 40'b01100010_01010001_01001001_01001001_01000110;
       4'h3: dots <= 40'b00100010_01000001_01001001_01001001_00110110;
       4'h4: dots <= 40'b00011000_00010100_00010010_01111111_00010000;
       4'h5: dots <= 40'b00100111_01000101_01000101_01000101_00111001;
       4'h6: dots <= 40'b00111100_01001010_01001001_01001001_00110000;
       4'h7: dots <= 40'b00000001_01110001_00001001_00000101_00000011;
       4'h8: dots <= 40'b00110110_01001001_01001001_01001001_00110110;
       4'h9: dots <= 40'b00000110_01001001_01001001_00101001_00011110;
       4'hA: dots <= 40'b01111110_00001001_00001001_00001001_01111110;
       4'hB: dots <= 40'b01111111_01001001_01001001_01001001_00110110;
       4'hC: dots <= 40'b00111110_01000001_01000001_01000001_00100010;
       4'hD: dots <= 40'b01111111_01000001_01000001_01000001_00111110;
       4'hE: dots <= 40'b01111111_01001001_01001001_01001001_01000001;
       4'hF: dots <= 40'b01111111_00001001_00001001_00001001_00000001;
     endcase
   
endmodule