Re: [Discuss-gnuradio] C++ General Blocks and the forecast() function

[Ron Economos]

Mert,

10/3 isn't an integer, so that's not going to work. Here's a correct scheme.

In the constructor:

set_output_multiple(54);

In forecast:

ninput_items_required[0] = (noutput_items / 54) * 180;

In work:

for (int i = 0; i < noutput_items; i += 54) {
  /* The processing needs to read 180 items from *in and write 54 items to *out */

}

consume_each ((noutput_items / 54) * 180);

Ron

On 10/31/18 17:58, Salahi, Mert E wrote:

Hi all,

 

I am trying to make a custom block that implements a MELP vocoder. The block takes in audio samples(floats) at 8kHz and outputs bits at 2.4kbps. Given that, I think I will need to use a general block to get the correct input/output buffer sizes.

 

The vocoder blocks the audio input to 22.5ms (180 samples) and outputs 54 bits. I know that I will need to modify the forecast() function, but I am not sure how. My guess would be something like this:

 

void

  gr::block::forecast(int noutput_items,

                     gr_vector_int &ninput_items_required)

  {

    unsigned ninputs = ninput_items_required.size ();

    for(unsigned i = 0; i < ninputs; i++)

      ninput_items_required[i] = (10/3)*noutput_items;

  }

 

Then call,

 

consume_each ((10/3)*noutput_items);

 

Is this the correct approach or am I missing something here? Once I get this working I will likely try to pack the bits into some integer data type for efficiency’s sake - so I’ll need to be to do this for different input/output ratios other than 10/3.

 

Thanks!