POSLink.v

   1 module POSLink(
   2         input xtal,
   3         input [3:0] tos_inputs_e2,
   4         input serial_e2,
   5         input [1:0] buttons,
   6         output tos_output,
   7         output reg data_output,
   8         output reg [3:0] anode,
   9         output reg [7:0] cathode);
  10
  11         reg [3:0] tos_inputs_e;
  12         reg [3:0] tos_inputs;
  13         reg serial_e;
  14         reg serial;
  15
  16         wire [3:0] tos_good;
  17
  18         /* Synchronize inputs */
  19         always @(posedge xtal) begin
  20                 tos_inputs_e <= tos_inputs_e2;
  21                 tos_inputs <= tos_inputs_e;
  22                 serial_e <= serial_e2;
  23                 serial <= serial_e;
  24         end
  25
  26         wire [11:0] data;
  27         wire data_good;
  28
  29         reg [1:0] seg;
  30
  31         always @(*)
  32                 case (seg)
  33                 2'b00:  anode = 4'b0111;
  34                 2'b01:  anode = 4'b1011;
  35                 2'b10:  anode = 4'b1101;
  36                 2'b11:  anode = 4'b1110;
  37                 endcase
  38
  39         reg [1:0] tos_select;
  40
  41         wire [3:0] current_bit;
  42
  43         assign tos_output = tos_inputs_e2[tos_select];
  44
  45         always @(*) begin
  46                 cathode = data[7:0];
  47                 seg = data[9:8];
  48                 tos_select = data[11:10];
  49         end
  50
  51         wire [5:0] output_stuff = { buttons, tos_good };
  52
  53         always @(*)
  54                 data_output = output_stuff[current_bit[2:0]];
  55
  56         TOS_Detect detect[3:0](.xtal(xtal), .tos_input(tos_inputs), .tos_good(tos_good));
  57         POS_Serial serinput(.xtal(xtal), .serial(serial), .data_reg(data), .current_bit(current_bit), .data_good(data_good));
  58 endmodule
  59
  60
  61 module POS_Serial(
  62         input xtal,
  63         input serial,
  64         output reg [11:0] data_reg = 0,
  65         output reg [3:0] current_bit = 0,
  66         output reg data_good = 0);
  67
  68         reg serial_1a;
  69
  70         always @(posedge xtal)
  71                 serial_1a = serial;
  72
  73         wire edge_detect = serial ^ serial_1a;
  74
  75         reg [4:0] edge_counter = 0;
  76
  77         always @(posedge xtal) begin
  78                 data_good = 0;
  79
  80                 if (edge_detect) begin
  81                         if (edge_counter == 31) begin
  82                                 current_bit = 0;
  83                                 data_reg = 0;
  84                         end else begin
  85                 //              data_reg[11:1] = data_reg[10:0];
  86                 //              data_reg[0] = (edge_counter > 20);
  87                                 data_reg[current_bit] = (edge_counter > 20);
  88                                 if (current_bit == 11) begin
  89                                         data_good = 1;
  90                                         current_bit = 0;
  91                                 end else
  92                                         current_bit = current_bit + 1;
  93                         end
  94
  95                         edge_counter = 0;
  96                 end else begin
  97                         if (edge_counter != 31)
  98                                 edge_counter = edge_counter + 1;
  99                 end
 100         end
 101 endmodule
 102
 103
 104 /* xtal: 25MHz (==40ns)
 105  * Minimum: 100ns
 106  *          2 cycles (80 ns)
 107  * Maximum: 1000ns
 108  *          25 cycles (we'll allow 30 = 1200ns for good measure)
 109  */
 110 module TOS_Detect(
 111         input xtal,
 112         input tos_input,
 113         output reg tos_good = 0);
 114
 115         reg tos_input_1a = 0;
 116         always @(posedge xtal)
 117                 tos_input_1a <= tos_input;
 118         wire transition = tos_input ^ tos_input_1a;
 119
 120         reg [3:0] lasttx = 0;
 121         always @(posedge xtal) begin
 122                 if (transition) begin
 123                         if (lasttx < 2) /* Too soon! */
 124                                 tos_good <= 0;
 125                         else if (lasttx > 30) /* Too late! */
 126                                 tos_good <= 0;
 127                         else /* OK by me. */
 128                                 tos_good <= 1;
 129                         lasttx <= 0;
 130                 end else begin
 131                         if (lasttx != 31)
 132                                 lasttx <= lasttx + 1;
 133                         else
 134                                 tos_good <= 0;
 135                 end
 136         end
 137 endmodule
 138