FSM设计之二-----并行数据流转特殊串行数据流

夏宇闻《Verilog 数字系统设计教程》P216

设计两个可综合电路模块：M1模块能把4位的并行数据转换为符合以下协议的串行数据流，数据流用scl和sda两条线传输，sclk为输入的时钟信号，data[3:0]为输入数据，ack为M1的请求M0发新数据信号。第二个模块M2能把串行数据流内的信息接收到，并转换为相应16条信号线的高电平，即若数据为1，则第一条线路为高电平，数据为n，则第n条数据线为高电平。M0为 测试用的信号发生模块，该模块接收M1发出的ack信号，并产生新的测试数据data[3:0]。

通信协议：scl为不断输出的时钟信号，如果scl为高电平时，sda由高变低时刻，串行数据流开始；如果scl为高电平时，sda由低变高时刻，串行数据流结束。sda信号的串行数据位必须在scl为低电平时变化，若变为高则为1，否则为0。

M1模块的代码如下

  1 `timescale 1ns/1ns
  2 module ptosda
  3 (
  4     input sclk,
  5     input rst_n,
  6     input [3:0] data,
  7     output reg ack,
  8     output reg scl,
  9     output sda
 10 );
 11 
 12 reg link_sda;
 13 reg sdabuf;
 14 reg [3:0] databuf;
 15 reg [7:0] state;
 16 
 17 parameter ready = 8'b0000_0001,
 18         start = 8'b0000_0010,
 19         bit1  = 8'b0000_0100,
 20         bit2  = 8'b0000_1000,
 21         bit3  = 8'b0001_0000,
 22         bit4  = 8'b0010_0000,
 23         bit5  = 8'b0100_0000,
 24         stop  = 8'b1000_0000,
 25         idle  = 8'b0000_0000;
 26 
 27 assign sda = link_sda?sdabuf:1'bz;
 28 
 29 always @ (posedge sclk,negedge rst_n)
 30 begin
 31     if(!rst_n)    scl <= 1'b1;
 32     else            scl <= ~scl;
 33 end
 34 
 35 always @ (posedge ack)
 36 begin
 37     databuf <= data;
 38 end
 39 
 40 always @ (negedge sclk or negedge rst_n)
 41 begin
 42     if(!rst_n)
 43     begin
 44         link_sda<=1'b0;
 45         state <= ready;
 46         sdabuf<=1'b1;
 47         ack<=1'b0;
 48     end
 49     else
 50     begin
 51         case(state)
 52         ready:
 53             if(ack)
 54             begin
 55                 link_sda<=1'b1;
 56                 state <= start;
 57             end
 58             else
 59             begin
 60                 link_sda<=1'b0;
 61                 state<=ready;
 62                 ack<=1'b1;
 63             end
 64         start:
 65             if(scl && ack)
 66             begin
 67                 sdabuf<=1'b0;
 68                 state<=bit1;
 69             end
 70             else        state<= start;
 71         bit1:
 72             if(!scl)
 73             begin
 74                 sdabuf<=databuf[3];
 75                 state<=bit2;
 76                 ack<=1'b0;
 77             end
 78             else        state<=bit1;
 79         bit2:
 80             if(!scl)
 81             begin
 82                 sdabuf<=databuf[2];
 83                 state<=bit3;
 84             end
 85             else        state<=bit2;
 86         bit3:
 87             if(!scl)
 88             begin
 89                 sdabuf<=databuf[1];
 90                 state<=bit4;
 91             end
 92             else        state<=bit3;
 93         bit4:
 94             if(!scl)
 95             begin
 96                 sdabuf<=databuf[0];
 97                 state<=bit5;
 98             end
 99             else        state<=bit4;
100         bit5:
101             if(!scl)
102             begin
103                 sdabuf<=1'b0;
104                 state<=stop;
105             end
106             else        state<=bit5;
107         stop:
108             if(scl)
109             begin
110                 sdabuf<=1'b1;
111                 state<=idle;
112             end
113             else        state<=stop;
114         idle:
115             begin
116                 link_sda<=1'b0;
117                 state<=ready;
118             end
119         default:
120             begin
121                 link_sda<=1'b0;
122                 sdabuf<=1'b1;
123                 state<=ready;
124             end
125         endcase
126     end
127 end
128 
129 endmodule

M2模块的代码如下

  1 `timescale 1ns/1ns
  2  module out16hi
  3 (
  4     input scl,
  5     input sda,
  6     output reg [15:0] outhigh,
  7     output reg [3:0] pdata,
  8     output reg [3:0] pdatabuf,
  9     output reg start_flag,
 10     output reg end_flag,
 11     output reg [5:0] mstate
 12 );
 13 
 14  //reg [5:0] mstate;/* synthesis preserve*/
 15  //reg [3:0] pdatabuf;
 16  //reg start_flag,end_flag;
 17  
 18 always @ (negedge sda)
 19 begin
 20     if(scl)    
 21         start_flag<=1'b1;
 22     else if(end_flag)    
 23         start_flag<=1'b0;
 24 end
 25 
 26 always @ (posedge sda)
 27 begin
 28     if(scl)
 29     begin
 30         end_flag<=1'b1;
 31         pdatabuf<=pdata;
 32     end
 33     else
 34         end_flag<=1'b0;
 35 end 
 36 
 37 parameter ready = 6'b00_0000,
 38             bit0  = 6'b00_0001,
 39             bit1  = 6'b00_0010,
 40             bit2  = 6'b00_0011,
 41             bit3  = 6'b00_0100,
 42             bit4  = 6'b00_0101;
 43         
 44 always @ (pdatabuf)
 45 begin
 46     case(pdatabuf)
 47         4'b0001 : outhigh = 16'b0000_0000_0000_0001;
 48         4'b0010 : outhigh = 16'b0000_0000_0000_0010;
 49         4'b0011 : outhigh = 16'b0000_0000_0000_0100;
 50         4'b0100 : outhigh = 16'b0000_0000_0000_1000;
 51         4'b0101 : outhigh = 16'b0000_0000_0001_0000;
 52         4'b0110 : outhigh = 16'b0000_0000_0010_0000;
 53         4'b0111 : outhigh = 16'b0000_0000_0100_0000;
 54         4'b1000 : outhigh = 16'b0000_0000_1000_0000;
 55         4'b1001 : outhigh = 16'b0000_0001_0000_0000;
 56         4'b1010 : outhigh = 16'b0000_0010_0000_0000;
 57         4'b1011 : outhigh = 16'b0000_0100_0000_0000;
 58         4'b1100 : outhigh = 16'b0000_1000_0000_0000;
 59         4'b1101 : outhigh = 16'b0001_0000_0000_0000;
 60         4'b1110 : outhigh = 16'b0010_0000_0000_0000;
 61         4'b1111 : outhigh = 16'b0100_0000_0000_0000;
 62         4'b0000 : outhigh = 16'b1000_0000_0000_0000;
 63     endcase
 64 end
 65 
 66 always @ (posedge scl)
 67 begin
 68     if(start_flag)
 69     case(mstate)
 70         bit0:
 71             begin
 72                 mstate <= bit1;
 73                 pdata[3] <= sda;
 74                 $display("I am is sda bit0");
 75             end
 76         bit1:
 77             begin
 78                 mstate <= bit2;
 79                 pdata[2] <= sda;
 80                 $display("I am is sda bit1");
 81             end
 82         bit2:
 83             begin
 84                 mstate <= bit3;
 85                 pdata[1] <= sda;
 86                 $display("I am is sda bit2");
 87             end
 88         bit3:
 89             begin
 90                 mstate <= bit4;
 91                 pdata[0] <= sda;
 92                 $display("I am is sda bit3");
 93             end
 94         bit4:
 95             begin    
 96                 mstate <= bit0;
 97                 $display("I am is sda stop");
 98             end
 99         default:
100                 mstate <= bit0;
101     endcase
102     else 
103        mstate <= bit0;
104 end 
105 
106 endmodule

信号测试模块：

`timescale 1ns/1ns
`define half 50
module sigdata
(
	input ask_for_data,
	output reg rst_n,
	output reg sclk,
	output reg [3:0] data
); 
//parameter half=50;
initial
begin
	rst_n=1;
	#10 rst_n=0;
	#(`half*2+3) rst_n=1;
end 

initial
begin
	sclk=0;
	data=0;
	#(`half*1000) $stop;
end 

always #(`half) sclk =~sclk;

always @ (posedge ask_for_data)
begin
	#(`half/2+3) data=data+1'b1;
end 

endmodule
顶层模块：
 1 `timescale 1ns/1ns
 2  module top;
 3 wire [3:0] data;
 4 wire sclk,scl,sda;
 5 wire rst_n;
 6 wire [15:0] outhigh;
 7 wire [3:0] pdata;
 8 wire [3:0] pdatabuf;
 9 wire start_flag,end_flag;
10 wire [5:0] mstate;
11 
12 sigdata M0
13 (
14     .rst_n(rst_n),
15     .sclk(sclk),
16     .data(data),
17     .ask_for_data(ack)
18 );
19 
20 ptosda M1
21 (
22     .rst_n(rst_n),
23     .sclk(sclk),
24     .ack(ack),
25     .scl(scl),
26     .sda(sda),
27     .data(data)
28 );
29 
30 out16hi M2
31 (
32     .scl(scl),
33     .sda(sda),
34     .outhigh(outhigh),
35     .pdata(pdata),
36     .pdatabuf(pdatabuf),
37     .start_flag(start_flag),
38     .end_flag(end_flag),
39     .mstate(mstate)
40 );
41 
42 endmodule

仿真结果：

在模块M2的状态机中，如果if（start_flag)没有加上else mstate<=bit0;就会发生状态跳转不正常的现象，只有第一次状态转移正确。

 1 always @ (posedge scl)
 2  begin
 3     if(start_flag)
 4     case(mstate)
 5         bit0:
 6             begin
 7                 mstate <= bit1;
 8                 pdata[3] <= sda;
 9                 $display("I am is sda bit0");
10             end
11         bit1:
12             begin
13                 mstate <= bit2;
14                 pdata[2] <= sda;
15                 $display("I am is sda bit1");
16             end
17         bit2:
18             begin
19                 mstate <= bit3;
20                 pdata[1] <= sda;
21                 $display("I am is sda bit2");
22             end
23         bit3:
24             begin
25                 mstate <= bit4;
26                 pdata[0] <= sda;
27                 $display("I am is sda bit3");
28             end
29         bit4:
30             begin    
31                 mstate <= bit0;
32                 $display("I am is sda stop");
33             end
34         default:
35                 mstate <= bit0;
36     endcase
37 end

就会出现下面的结果：

 FSM的设计，用状态变量来记住曾经发生过的事情，这些曾经发生过的事情对于电路下一步时钟操作有非常重要的作用。

在本例程中，无论M1和M2模块的设计都必须用状态变量记住目前所处的状态，才能正确地控制输入和输出。可综合模块的设计必须在电路总体结构明确的情况下，

用状态机写出控制的节拍和步骤后才能进行。

posted on 2010-11-28 17:45  齐威王  阅读(2209)  评论(0)  编辑  收藏  举报

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