Sound2.v

   1 `define ADDR_NR21 16'hFF16
   2 `define ADDR_NR22 16'hFF17
   3 `define ADDR_NR23 16'hFF18
   4 `define ADDR_NR24 16'hFF19
   5
   6 module Sound2(
   7         input core_clk,
   8         input wr,
   9         input rd,
  10         input [15:0] addr,
  11         inout [7:0] data,
  12         input cntclk,
  13         input lenclk,
  14         input en,
  15         output [3:0] snd_data
  16         );
  17
  18         /* can be optimized as register file */
  19         reg [7:0] nr21, nr22, nr23, nr24;
  20         reg [10:0] counter = 0;
  21         reg [4:0] lencnt = 0;
  22         reg [3:0] delta = 4'b1111;
  23         reg [2:0] dutycnt;
  24         reg [3:0] snd_out = 0;
  25
  26         assign snd_data = en ? snd_out : 0;
  27
  28         assign data = rd ?
  29                          addr == `ADDR_NR21 ? nr21 :
  30                          addr == `ADDR_NR22 ? nr22 :
  31                          addr == `ADDR_NR23 ? nr23 :
  32                          addr == `ADDR_NR24 ? nr24 : 8'bzzzzzzzz
  33                       : 8'bzzzzzzzz;
  34
  35         always @ (negedge core_clk) begin
  36                 if(en && wr) begin
  37                         case(addr)
  38                         `ADDR_NR21: nr21 <= data;
  39                         `ADDR_NR22: nr22 <= data;
  40                         `ADDR_NR23: nr23 <= data;
  41                         `ADDR_NR24: nr24 <= data;
  42                         endcase
  43                 end
  44                 else if(!en) begin
  45                         nr21 <= 8'h3F;
  46                         nr22 <= 8'h00;
  47                         nr23 <= 8'hFF;
  48                         nr24 <= 8'hBF;
  49                 end
  50         end
  51
  52         always @ (posedge cntclk) begin
  53                 if(counter)
  54                         counter <= counter - 1;
  55                 else begin
  56                         counter <= ~{nr24[2:0],nr23} + 1;  /* possible A */
  57                         dutycnt <= dutycnt + 1;
  58                 end
  59
  60                 case (nr21[7:6])
  61                 2'b00: snd_out <= dutycnt ? 0 : delta;   /* probable A */
  62                 2'b01: snd_out <= (dutycnt[2:1] == 2'b0) ? delta : 0;
  63                 2'b10: snd_out <= dutycnt[2] ? delta : 0;
  64                 2'b11: snd_out <= (dutycnt[2:1] == 2'b0) ? 0 : delta;
  65                 endcase
  66         end
  67
  68         always @ (posedge lenclk) begin
  69                 if(lencnt)
  70                         lencnt <= lencnt - 1;            /* possible A */
  71                 else
  72                         lencnt <= ~nr21[4:0] + 1;
  73         end
  74
  75 endmodule