Re: [Discuss-gnuradio] Please help building a signal processing block.

[Mikhail Tadjikov]

Thanks, but I'm trying to get weighted average specifically. I've looked at the code for moving_average... it's close to what I need, but its 1:1 in/out ratio, but I need N:1 ratio. That's the part I'm particular unclear about.

On Sat, Mar 28, 2009 at 9:27 AM, Karthik <address@hidden> wrote:

2009/3/27 Mikhail Tadjikov <address@hidden>

Hello,

 I'm trying to build several signal processing blocks for a project that I'm doing using USRP2.  I was going through the examples and sample code along with browsing the source code and I can't seem to find exactly what I need. I'm trying to do an average of a vector of length N:

Input vector size N
Output vector size 1
I'm doing it for floats.

------------------------------
#ifndef INCLUDED_CORES_WEIGHTED_AVG_FF_H
#define INCLUDED_CORES_WEIGHTED_AVG_FF_H
#include <gr_sync_block.h>
class cores_weighted_avg_ff;

typedef boost::shared_ptr<cores_weighted_avg_ff> cores_weighted_avg_ff_sptr;
cores_weighted_avg_ff_sptr cores_make_weighted_avg_ff (unsigned int vlen);

class cores_weighted_avg_ff : public gr_sync_block
{
private:
   friend cores_weighted_avg_ff_sptr cores_make_weighted_avg_ff (unsigned int vlen);
  cores_weighted_avg_ff (unsigned int vlen);      // private constructor
  unsigned int d_vlen;
   
 public:
  int general_work (int noutput_items,
                        gr_vector_int &ninput_items,
                        gr_vector_const_void_star &input_items,
                        gr_vector_void_star &output_items);
};
#endif
----------------------------------------------------------------------------------------------------------
and source
-------------------------------------------------------------------------------------------
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
#include <cores_weighted_avg_ff.h>
#include <gr_io_signature.h>

cores_weighted_avg_ff_sptr
cores_make_weighted_avg_ff (unsigned int vlen)
{  return cores_weighted_avg_ff_sptr (new cores_weighted_avg_ff (vlen));}
   
cores_weighted_avg_ff::cores_weighted_avg_ff (unsigned int vlen)
  : gr_decimator_block ("weighed_avg_ff",
                   gr_make_io_signature (1, 1, sizeof (float) * vlen),
                   gr_make_io_signature (1, 1, sizeof (float))),
    d_vlen(vlen)
{
}
int
cores_weighted_avg_ff::int 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 noi = noutput_items * d_vlen;
   
      for (int i = 0; i < noi; i++){
        out += in[i]*i;
      }
      out /= d_vlen;
      consume(noutput_items,d_vlen)

      return noutput_items;
}
------------------------------------------------------------------------------------------------

I'm not sure if the code is correct what I want to do (input is more than welcome), when I compile this code I get a weird error:
cores_weighted_avg_ff.h: In function ‘PyObject* _wrap_weighted_avg_ff(PyObject*, PyObject*)’:
cores_weighted_avg_ff.h:63: error: too few arguments to function ‘cores_weighted_avg_ff_sptr cores_make_weighted_avg_ff(unsigned int)’
cores.cc:4326: error: at this point in file
make[4]: *** [cores.lo] Error 1

Any help would be greatly appreciated.

With gr_sync_block you only need to write work() and not general_work(). The example at the end of this tutorial will be helpful http://www.gnu.org/software/gnuradio/doc/howto-write-a-block.html. Also, there is a "#endif" sitting in the middle of your code, it might be a typo.

btw, if you are trying to get moving averages, there is a block already available gr_moving_averages()

Karthik
 

-- 
Mikhail Tadjikov
Graduate Student
UCLA Department of 
Electrical Engineering