关于处理视频断流的一些思考

虽然大部分摄像头都不支持热拔插，但我觉得思考一下相关问题还是有意义的。

先说结论：处理断流的根本在于同步信号。

正所谓，输入端通常会有同步头、同步行之类的时间串口，通过对这个期间的信号做处理以后使用其上升沿作为标志，用来重置存储地址和FIFO是处理输入同步的有效方法。

代码：

 1     //W Sync Port
 2     //wrclk
 3     reg                               r1_pre_vs        ;
 4     wire                              Pose_pre_vs      ;
 5     wire                              Nege_pre_vs      ;
 6     wire                              Ext_Pose_pre_vs  ;
 7     //sysclk
 8     reg                               sys_pre_vs       ;
 9     reg                               r1_sys_pre_vs    ;
10     reg                               sys_Pose_pre_vs  ;
11     reg                               sys_Nege_pre_vs  ;
12     reg                               r_sys_Nege_pre_vs;
13     reg  [1:0]                        wr_index         ;
14     reg   [C_M_AXI_ADDR_WIDTH-1 : 0]  wr_base_addr     ;
15     
16     always @(posedge I_Pre_clk) begin
17         r1_pre_vs <= I_Pre_vs;
18     end
19 
20     assign  Pose_pre_vs = (I_Pre_vs == 1'b1)&&(r1_pre_vs == 1'b0);
21     assign  Nege_pre_vs = (I_Pre_vs == 1'b0)&&(r1_pre_vs == 1'b1);
22 
23     always@(posedge M_AXI_ACLK) begin
24         sys_pre_vs        <= I_Pre_vs  ;
25         r1_sys_pre_vs     <= sys_pre_vs;
26         r_sys_Nege_pre_vs <= sys_Nege_pre_vs;
27     end
28 
29     always @(posedge M_AXI_ACLK) begin
30         if(M_AXI_ARESETN == 1'b0) begin
31             sys_Pose_pre_vs <= 1'b0;
32             sys_Nege_pre_vs <= 1'b0;
33         end else if(sys_pre_vs==1'b1&&r1_sys_pre_vs==1'b0) begin
34             sys_Pose_pre_vs <= 1'b1;
35             sys_Nege_pre_vs <= 1'b0; 
36         end else if(sys_pre_vs==1'b0&&r1_sys_pre_vs==1'b1) begin
37             sys_Pose_pre_vs <= 1'b0;
38             sys_Nege_pre_vs <= 1'b1; 
39         end else begin
40             sys_Pose_pre_vs <= 1'b0;
41             sys_Nege_pre_vs <= 1'b0;
42         end
43     end
44 
45 
46     Data_sync_ext Data_sync_ext_Inst0(
47         .clka           ( I_Pre_clk          ),
48         .rst_n          ( M_AXI_ARESETN      ),    
49         .pulse_a        ( Pose_pre_vs        ),
50         .ext_pulse_a    ( Ext_Pose_pre_vs    )
51     );
52 
53     always@(posedge M_AXI_ACLK)
54         if(M_AXI_ARESETN == 1'b0) begin
55             wr_index <= 'd1;
56         end else if(sys_Nege_pre_vs == 1'b1&&wr_index == AXI_Buff_NUM) begin
57             wr_index <= 'd1;
58         end else if(sys_Nege_pre_vs==1'b1) begin
59             wr_index <= wr_index + 1'b1;
60         end else begin
61             wr_index <= wr_index;
62         end
63 
64         assign  O_wr_index = wr_index;
65             
66     always@(posedge M_AXI_ACLK)
67         if(M_AXI_ARESETN == 1'b0) begin
68             wr_base_addr <= 0;
69         end    else if(sys_Nege_pre_vs == 1'b1&&wr_index == AXI_Buff_NUM) begin
70             wr_base_addr <= 0;
71         end else if(sys_Nege_pre_vs == 1'b1) begin
72             wr_base_addr <= wr_base_addr + Total_Frame_Offset;
73         end else begin
74             wr_base_addr <= wr_base_addr;
75         end

而处理输出就比较简单了，因为是你自己定义的，自己生成或使用现有的VGA或其他接口的同步帧即可。