tests/ctags/state_machine.v

   1 // Taken from http://www.europa.com/~celiac/fsm_samp.html
   2
   3 // These are the symbolic names for states
   4 parameter  [1:0]       //synopsys enum state_info
   5   S0 = 2'h0,
   6   S1 = 2'h1,
   7   S2 = 2'h2,
   8   S3 = 2'h3;
   9
  10 // These are the current state and next state variables
  11 reg [1:0] /* synopsys enum state_info */ state;
  12 reg [1:0] /* synopsys enum state_info */ next_state;
  13
  14
  15 // synopsys state_vector state
  16
  17 always @ (state or y or x)
  18 begin
  19   next_state = state;
  20   case (state)                 // synopsys full_case parallel_case
  21     S0: begin
  22       if (x) begin
  23         next_state = S1;
  24       end
  25       else begin
  26
  27         next_state = S2;
  28       end
  29     end
  30     S1: begin
  31       if (y) begin
  32         next_state = S2;
  33       end
  34       else begin
  35         next_state = S0;
  36       end
  37     end
  38     S2: begin
  39       if (x & y) begin
  40         next_state = S3;
  41       end
  42       else begin
  43         next_state = S0;
  44       end
  45     end
  46     S3: begin
  47       next_state = S0;
  48     end
  49   endcase
  50 end
  51
  52
  53 always @ (posedge clk or posedge reset)
  54 begin
  55   if (reset) begin
  56     state <= S0;
  57   end
  58   else begin
  59     state <= next_state;
  60   end
  61 end