[Discuss-gnuradio] amplitude block returns instable values

[Georg von Zengen]

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Hi,

I am trying to calculate the amplitude of a sine-signal.
In grc the scope shows a instable value jumping between 0 and the real
amplitude.
My code is in the attachment.

regards
Georg
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/* -*- c++ -*- */
/*
 * Copyright 2004 Free Software Foundation, Inc.
 * 
 * This file is part of GNU Radio
 * 
 * GNU Radio is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 3, or (at your option)
 * any later version.
 * 
 * GNU Radio is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with GNU Radio; see the file COPYING.  If not, write to
 * the Free Software Foundation, Inc., 51 Franklin Street,
 * Boston, MA 02110-1301, USA.
 */

/*
 * config.h is generated by configure.  It contains the results
 * of probing for features, options etc.  It should be the first
 * file included in your .cc file.
 */
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
#include <isa_amp_vff.h>
#include <gr_io_signature.h>
#include <stdio.h>


/*
 * Create a new instance of isa_amp_vff and return
 * a boost shared_ptr.  This is effectively the public constructor.
 */
isa_amp_vff_sptr 
isa_make_amp_vff (int vlen)
{
  return isa_amp_vff_sptr (new isa_amp_vff (vlen));
}

/*
 * 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
 */
isa_amp_vff::isa_amp_vff (int vlen)
  : gr_block ("amp_vff",
              gr_make_io_signature (MIN_IN, MAX_IN, sizeof (float)*vlen),
              gr_make_io_signature (MIN_OUT, MAX_OUT, sizeof (float)))
{
  // nothing else required in this example
                                d_amp_vlen=vlen;
}

/*
 * Our virtual destructor.
 */
isa_amp_vff::~isa_amp_vff ()
{
  // nothing else required in this example
}

int isa_amp_vff::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];
        double h_amp=0, l_amp=0;
        for (int i = 1; i < d_amp_vlen; i++){
                if ( in[i] > h_amp ){
                        h_amp=in[i];
                }else if ( in[i] < l_amp ){
                        l_amp=in[i];
                }
          }
        out[0]=h_amp+(l_amp*(-1));      


        
        // Tell runtime system how many input items we consumed on
        // each input stream.

        consume_each (noutput_items);

        // Tell runtime system how many output items we produced.
        return noutput_items;
}