I‘m need it too。can u analyze code as following：
*******************************************************************************/
/*******************************************************************************
The module generates noise,using downlink m-sequences.
The x sequence is constructed using the primitive polynomial
1 + x( 7 ) + x( 18 ).
The y sequence is constructed using the ploynomial
1 + x( 5 ) + x( 7 ) + x( 10 ) + x( 18 ).
x is iniatialized with x( 0 ) = x( 1 ) = x( 2 ) ... = x( 17 ) = 0,
recursive definition
x( i+ 18 ) = x( i + 7 ) + x( i ) modulo 2.
y is iniatialized with y( 0 ) = y( 1 ) = y( 2 ) ... = y( 17 ) = 1.
recursive definition
y( i + 18 ) = y( i + 10 ) + y( i+ 7 ) + y( i+ 5 ) + y( i ) modulo 2.
Noise output is z( i ) = x( i ) + y( i ) modulo 2.
*******************************************************************************/
module GEN_NOISE (
// input data
Clk16,
Reset,
Node_sync,
Channel_noise,
// output data
Noise_data
)/* synthesis syn_hier = "hard" */;
input Clk16;
input Reset;
input Node_sync;
input [9:0] Channel_noise;
// output data
output [9:0] Noise_data;
reg [9:0] Noise_data;
reg Noise_start;
reg [ 17:0 ] Xseq;
reg [ 17:0 ] Yseq;
wire [ 1:0 ] Xshift;
wire [ 2:0 ] Yshift;
wire [ 1:0 ] Noise_out;
wire [9:0] N_NOISE_ENG;
// module begin.
//******************************************************************************
////////////////////////////////////////////////////////////////////////////////
// Wait node synchronous signal.
always @( posedge Clk16 or posedge Reset )
begin
if( Reset == 1'b1 )
Noise_start <= 1'b0;
else
if( Node_sync == 1'b1 )
Noise_start <= 1'b1;
else;
end
////////////////////////////////////////////////////////////////////////////////
//******************************************************************************
//******************************************************************************
////////////////////////////////////////////////////////////////////////////////
// Generate x and y sequence.
assign Xshift = Xseq[ 7 ] + Xseq[ 0 ];
always @( posedge Clk16 or posedge Reset )
begin
if( Reset == 1'b1 )
Xseq <= 18'b0;
else
if( Noise_start == 1'b1 )
begin
Xseq[ 16:0 ] <= Xseq[ 17:1 ];
Xseq[ 17 ] <= Xshift[ 0 ];
end
else;
end
////////////////////////////////////////////////////////////////////////////////
assign Yshift = Yseq[ 10 ] + Yseq[ 7 ] + Yseq[ 5 ] + Yseq[ 0 ];
always @( posedge Clk16 or posedge Reset )
begin
if( Reset == 1'b1 )
Yseq <= 18'h3ffff;
else
if( Noise_start == 1'b1 )
begin
Yseq[ 16:0 ] <= Yseq[ 17:1 ];
Yseq[ 17 ] <= Yshift[ 0 ];
end
else;
end
////////////////////////////////////////////////////////////////////////////////
//******************************************************************************
// Generate noise data.
assign Noise_out = Xseq[ 0 ] + Yseq[ 0 ];
assign N_NOISE_ENG = ( ~ Channel_noise ) + 1 ;
always @( posedge Clk16 or posedge Reset )
begin
if( Reset == 1'b1 )
Noise_data <= 11'b0;
else
if( Noise_start == 1'b1 )
if ( Noise_out[ 0 ] == 1'b1 )
Noise_data <= N_NOISE_ENG;
else
Noise_data <= Channel_noise;
else
;
end
////////////////////////////////////////////////////////////////////////////////
endmodule // End GEN_NOISE