Spit lots of A out of the UART.
[fpgaboy.git] / 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         input [7:0] data,
12         output reg serial);
13
14         reg [7:0] data_stor = 0;
15         reg [15:0] clkdiv = 0;
16         reg have_data = 0;
17         reg data_end = 0;
18         reg [3:0] diqing = 4'b0000;
19         
20         wire new = (wr) && (!have_data) && (addr == `MMAP_ADDR);
21
22         always @ (negedge clk)
23         begin
24                 /* deal with diqing */
25                 if(new) begin
26                         data_stor <= data;
27                         have_data <= 1;
28                         diqing <= 4'b0000;
29                 end else if (clkdiv == 0) begin
30                         diqing <= diqing + 1;
31                         if (have_data)
32                                 case (diqing)
33                                 4'b0000: serial <= 0;
34                                 4'b0001: serial <= data_stor[0];
35                                 4'b0010: serial <= data_stor[1];
36                                 4'b0011: serial <= data_stor[2];
37                                 4'b0100: serial <= data_stor[3];
38                                 4'b0101: serial <= data_stor[4];
39                                 4'b0110: serial <= data_stor[5];
40                                 4'b0111: serial <= data_stor[6];
41                                 4'b1000: serial <= data_stor[7];
42                                 4'b1001: serial <= 1;
43                                 4'b1010: have_data <= 0;
44                                 default: $stop;
45                         endcase
46                 end
47
48                 /* deal with clkdiv */
49                 if((new && !have_data) || clkdiv == `CLK_DIV)
50                         clkdiv <= 0;
51                 else
52                         clkdiv <= clkdiv + 1;
53         end
54 endmodule
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