Uart.v

   1 `define IN_CLK 8388608
   2 `define OUT_CLK 9600
   3 `define CLK_DIV `IN_CLK / `OUT_CLK
   4 `define MMAP_ADDR 16'hFF50
   5
   6 module UART(
   7         input clk,
   8         input wr,
   9         input rd,
  10         input [15:0] addr,
  11         inout [7:0] data,
  12         output reg serial = 1);
  13
  14         wire decode = (addr == `MMAP_ADDR);
  15
  16         wire [7:0] odata;
  17         assign data = (rd && decode) ? odata : 8'bzzzzzzzz;
  18
  19         reg [7:0] data_stor = 0;
  20         reg [15:0] clkdiv = 0;
  21         reg have_data = 0;
  22         reg [3:0] diqing = 4'b0000;
  23
  24         wire new = (wr) && (!have_data) && decode;
  25
  26         assign odata = have_data ? 8'b1 : 8'b0;
  27
  28         always @ (negedge clk)
  29         begin
  30                 /* deal with diqing */
  31                 if(new) begin
  32                         data_stor <= data;
  33                         have_data <= 1;
  34                         diqing <= 4'b0000;
  35                 end else if (clkdiv == 0) begin
  36                         diqing <= diqing + 1;
  37                         if (have_data)
  38                                 case (diqing)
  39                                 4'b0000: serial <= 0;
  40                                 4'b0001: serial <= data_stor[0];
  41                                 4'b0010: serial <= data_stor[1];
  42                                 4'b0011: serial <= data_stor[2];
  43                                 4'b0100: serial <= data_stor[3];
  44                                 4'b0101: serial <= data_stor[4];
  45                                 4'b0110: serial <= data_stor[5];
  46                                 4'b0111: serial <= data_stor[6];
  47                                 4'b1000: serial <= data_stor[7];
  48                                 4'b1001: serial <= 1;
  49                                 4'b1010: have_data <= 0;
  50                                 default: $stop;
  51                         endcase
  52                 end
  53
  54                 /* deal with clkdiv */
  55                 if((new && !have_data) || clkdiv == `CLK_DIV)
  56                         clkdiv <= 0;
  57                 else
  58                         clkdiv <= clkdiv + 1;
  59         end
  60 endmodule