///////////////////////////////////////////////////////////////////////////////
//
// 6.111 FPGA Labkit -- Hex display driver
//
// File:   display_16hex.v
// Date:   24-Sep-05
//
// Created: April 27, 2004
// Author: Nathan Ickes
//
// 24-Sep-05 Ike: updated to use new reset-once state machine, remove clear
// 28-Nov-06 CJT: fixed race condition between CE and RS (thanks Javier!)
//
// This verilog module drives the labkit hex dot matrix displays, and puts
// up 16 hexadecimal digits (8 bytes).  These are passed to the module
// through a 64 bit wire ("data"), asynchronously.  
//
///////////////////////////////////////////////////////////////////////////////

module display_16hex (reset, clock_27mhz, data, 
		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;		// 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 [4:0] count;
   reg [7:0] reset_count;
   reg clock;
   wire dreset;

   always @(posedge clock_27mhz)
     begin
	if (reset)
	  begin
	     count = 0;
	     clock = 0;
	  end
	else if (count == 26)
	  begin
	     clock = ~clock;
	     count = 5'h00;
	  end
	else
	  count = count+1;
     end
   
   always @(posedge clock_27mhz)
     if (reset)
       reset_count <= 100;
     else
       reset_count <= (reset_count==0) ? 0 : reset_count-1;

   assign dreset = (reset_count != 0);

   assign disp_clock = ~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
   
   assign disp_blank = 1'b0; // low <= not blanked
   
   always @(posedge clock)
     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
	      disp_rs <= 1'b1; // Select the control register
	      state <= state+1;
	   end
	 
	 8'h04:
	   begin
	      // Setup 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
	      state <= state+1;
	      disp_rs <= 1'b0;	 	// Select the dot register
	   end
	 
	 8'h06:
	   begin
	      // Load the user's dot data into the dot reg, char by char
	      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
		  dot_index <= 39;
		end
	      else
		dot_index <= dot_index-1;	// else loop thru all dots 
	   end

       endcase

   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