[Discuss-gnuradio] custom work function gets into an endless loop

[Kolya]

Hi,

I'm trying to build a custom block that takes in a stream of input samples
and simply adds a postamble of 32bits every 352 bits. The package structure
is illustrated below (payload_bits = msg_bits+postamble_bits):
---------------------------------------------------------------
|   msg_bits = 352         |  postamble_bits = 32  |
---------------------------------------------------------------

For some reason the code below gets into an endless loop when I run it
through a test and stimulate it with a non-repeating vector source. The
debug printf statements show that the loop keeps iterating even without
input.
I derived from gr_block because the number of output samples is higher than
the number of input samples and the work function is shown below:


/    void bbframer_bb_impl::general_work(int noutput_items,
        gr_vector_int &ninput_items,
        gr_vector_const_void_star &input_items,
        gr_vector_void_star &output_items)
    {
      const unsigned char *in = (const unsigned char *) input_items[0];
      unsigned char *out = (unsigned char *) output_items[0];
      int out_offset = 0;
      int consumed = 0;

      for (int i = 0; i < noutput_items; i += (int)(payload_bits/8)) {

          for (int j = 0; j < (int)(msg_bits / 8); j++) {               // 
Input index loop
(byte-index)

                  out[out_offset++]=in[consumed++];
          }
          // now add add postamble
          out[out_offset++]=0x00;
          out[out_offset++]=0x01;
          out[out_offset++]=0x02;
          out[out_offset++]=0x03;
      }
#ifdef VERBOSE
      printf(">>> offset= %d\n",out_offset);
      printf(">>> consumed= %d\n",consumed);
#endif

      this->consume_each(consumed);
      return out_offset;
}/

I also overrode the forecast function to account for the fact that fewer
input samples are needed than output samples are produced:

/    void
    bbframer_bb_impl::forecast (int noutput_items, gr_vector_int
&ninput_items_required)
    {
        ninput_items_required[0] = ((noutput_items - 32) / 8); // 32 bit
postamble
    }/


Any feedback would be greatly appreciated.
- Kolya



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