Hi Tom:
Thanks for your reply. Can you tell me how to fix it? May be I looked at
my code too much, I do not know where to change.
inter
From: [email protected]
Date: Mon, 12 Sep 2011 22:42:39 -0400
Subject: Re: [Discuss-gnuradio] a question about using new block in GNURadio
To: [email protected]
CC: [email protected]
2011/9/12 intermilan <[email protected]>
Hi all:
I wrote a new block and add it into the GnuRadio. The function of this
block is to synchronize the spread signal,
which means this block used local PN sequence to correlate the input signal.
And I set the threshold, if the correlation value is
larger than the threshold, that means I finish the synchronous part. Then use
the local PN sequence to XOR the synchronized
signal, so we will get the de-spread signal.
But there is a problem I can not figure out the reason. I test this block
in GRC. This block can works well in short time. Then
sometimes the value of the output of this block would become 0. And I do not
know the reason of this situation. I put my code
of the block in this e-mail.
I hope someone can help me to find out where is the problem of my code.
Thank you in advance.
Just a very quick read-through, but it looks like you are advancing i too much.
You're going to walk it out of bounds of the input buffer.
Tom
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
#include <pn_correlator1_ff.h>
#include <gr_io_signature.h>
#include <vector>
#include <iostream>
#include <fstream>
/*
* Create a new instance of pn_correlator_cc and return
* a boost shared_ptr. This is effectively the public constructor.
*/
pn_correlator_ff_sptr
pn_make_correlator_ff (int degree, int mask, int seed)
{
return pn_correlator_ff_sptr (new pn_correlator1_ff (degree, mask, seed));
}
/*
* Specify constraints on number of input and output streams.
* This info is used to construct the input and output signatures
* (2nd & 3rd args to gr_block's constructor). The input and
* output signatures are used by the runtime system to
* check that a valid number and type of inputs and outputs
* are connected to this block. In this case, we accept
* only 1 input and 1 output.
*/
static const int MIN_IN = 1; // mininum number of input streams
static const int MAX_IN = 1; // maximum number of input streams
static const int MIN_OUT = 1; // minimum number of output streams
static const int MAX_OUT = 1; // maximum number of output streams
/*
* The private constructor
*/
pn_correlator_ff::pn_correlator_ff (int degree, int mask, int seed)
: gr_block("correlator_ff",
gr_make_io_signature (MIN_IN, MAX_IN, sizeof (float)),
gr_make_io_signature (MIN_OUT, MAX_OUT, sizeof (float)))
{
d_len = (unsigned int)((1ULL << degree)-1);
d = degree;
if (mask == 0)
mask = gri_glfsr::glfsr_mask(degree);
d_reference = new gri_glfsr(mask, seed);
for (int i = 0; i < d_len; i++) // initialize to last value in sequence
d_pn = 2.0*d_reference->next_bit()-1.0;
}
void
pn_correlator_ff::forecast (int noutput_items, gr_vector_int
&ninput_items_required)
{
int input_required = noutput_items + d*d_len ;
unsigned ninputs = ninput_items_required.size();
for (unsigned int i = 0; i < ninputs; i++) {
ninput_items_required[i] = input_required;
}
}
/*
* Our virtual destructor.
*/
pn_correlator_ff::~pn_correlator_ff()
{
delete d_reference;
}
int
pn_correlator_ff::general_work (int noutput_items,
gr_vector_int &ninput_items,
gr_vector_const_void_star &input_items,
gr_vector_void_star &output_items)
{
const float *in = (const float *) input_items[0];
float *out = (float *) output_items[0];
int a=0;
int i=0;
float sum =0;
while(a<noutput_items)
{
while(sum<0.8)
{
sum =0;
for (int j = 0; j < d_len; j++) {
if (j != 0) // retard PN generator one
sample per period
d_pn = 2.0*d_reference->next_bit()-1.0; // no conditionals
sum+= (2*(in[i])-1) * d_pn;
i++;
}
sum = abs(sum/d_len); //calculate the correlate value
}
d_pn = d_reference->next_bit();
if(d_pn == in[i]) // use local PN sequence to XOR the synchronized signal
out[a]=0;
else
out[a]=1;
i++;
a++;
}
consume_each (noutput_items);
return noutput_items;
}
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