S03_CH04_AXI_DMA_OV5640摄像头采集系统信号延迟的问题
S03_CH04_AXI_DMA_OV5640摄像头采集系统的问题：我想问下在count_reset模块中parameternum = 20'hffff0我算了下这个参数 输入时钟25MHZ；20'hffff 等于1048560 ; (1/25000000)*1048560 = 42ms;为什么延迟这么多呢？
而 在cmos_decode模块中rst_n_i为什么反复寄存了四个时钟周期呢？
module count_reset#
(
parameternum = 20'hffff0
)(
input clk_i,
output rst_o
);
reg cnt = 20'd0;
reg rst_d0;
/*count for clock*/
always@(posedge clk_i)
begin
cnt <= ( cnt <= num)?( cnt + 20'd1 ):num;
end
/*generate output signal*/
always@(posedge clk_i)
begin
rst_d0 <= ( cnt >= num)?1'b1:1'b0;
end
assign rst_o = rst_d0;
endmodule
我想问下 parameternum = 20'hffff0我算了下这个参数 输入时钟25MHZ；20'hffff 等于1048560 ; (1/25000000)*1048560 = 42ms;为什么延迟这么多呢？
在下面的模块中rst_n_i为什么反复寄存了四个时钟周期呢`timescale 1ns / 1ps
//////////////////////////////////////////////////////////////////////////////////
// Company: milinker corperation
// WEB:www.milinker.com
// BBS:www.osrc.cn
// Engineer:.
// Create Date: 07:28:50 09/04/2015
// Design Name:cmos_decode_v1
// Module Name: cmos_decode_v1
// Project Name:cmos_decode_v1
// Target Devices: XC6SLX25-FTG256 Mis603
// Tool versions:ISE14.7
// Description:cmos_decode_v1.
// Revision:V1.0
// Additional Comments:
//1) _i PIN input
//2) _o PIN output
//3) _n PIN active low
//4) _dg debug signal
//5) _rreg delay
//6) _s state machine
//////////////////////////////////////////////////////////////////////////////
module cmos_decode(
//system signal.
input cmos_clk_i,//cmos senseor clock.
input rst_n_i,//system reset.active low.
//cmos sensor hardware interface.
input cmos_pclk_i,//input pixel clock.
input cmos_href_i,//input pixel hs signal.
input cmos_vsync_i,//input pixel vs signal.
inputcmos_data_i,//data.
output cmos_xclk_o,//output clock to cmos sensor.
//user interface.
output hs_o,//hs signal.
output vs_o,//vs signal.
output reg rgb565_o,//data output
output vid_clk_ce
);
parameterCMOS_FRAME_WAITCNT = 4'd15;
reg rst_n_reg = 5'd0;
//reset signal deal with.
always@(posedge cmos_clk_i)
begin
rst_n_reg <= {rst_n_reg,rst_n_i};
end
regvsync_d;
reghref_d;
wire vsync_start;
wire vsync_end;
//vs signal deal with.
always@(posedge cmos_pclk_i)
begin
vsync_d <= {vsync_d,cmos_vsync_i};
href_d<= {href_d,cmos_href_i};
end
assign vsync_start =vsync_d&(!vsync_d);
assign vsync_end = (!vsync_d)&vsync_d;
regcmos_fps;
//frame count.
always@(posedge cmos_pclk_i)
begin
if(!rst_n_reg)
begin
cmos_fps <= 7'd0;
end
else if(vsync_start)
begin
cmos_fps <= cmos_fps + 7'd1;
end
else if(cmos_fps >= CMOS_FRAME_WAITCNT)
begin
cmos_fps <= CMOS_FRAME_WAITCNT;
end
end
//wait frames and output enable.
reg out_en;
always@(posedge cmos_pclk_i)
begin
if(!rst_n_reg)
begin
out_en <= 1'b0;
end
else if(cmos_fps >= CMOS_FRAME_WAITCNT)
begin
out_en <= 1'b1;
end
else
begin
out_en <= out_en;
end
end
//output data 8bit changed into 16bit in rgb565.
reg cmos_data_d0;
reg cmos_rgb565_d0;
reg byte_flag;
always@(posedge cmos_pclk_i)
begin
if(!rst_n_reg)
byte_flag <= 0;
else if(cmos_href_i)
byte_flag <= ~byte_flag;
else
byte_flag <= 0;
end
reg byte_flag_r0;
always@(posedge cmos_pclk_i)
begin
if(!rst_n_reg)
byte_flag_r0 <= 0;
else
byte_flag_r0 <= byte_flag;
end
always@(posedge cmos_pclk_i)
begin
if(!rst_n_reg)
cmos_data_d0 <= 8'd0;
else if(cmos_href_i)
cmos_data_d0 <= cmos_data_i; //MSB -> LSB
else if(~cmos_href_i)
cmos_data_d0 <= 8'd0;
end
always@(posedge cmos_pclk_i)
begin
if(!rst_n_reg)
rgb565_o <= 16'd0;
else if(cmos_href_i&byte_flag)
rgb565_o <= {cmos_data_d0,cmos_data_i}; //MSB -> LSB
else if(~cmos_href_i)
rgb565_o <= 8'd0;
end
assign vid_clk_ce = out_en ? (byte_flag_r0&hs_o)||(!hs_o) : 1'b0;
assign vs_o = out_en ? vsync_d : 1'b0;
assign hs_o = out_en ? href_d : 1'b0;
assign cmos_xclk_o = cmos_clk_i;
endmodule
不错，感谢
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