Re: [Discuss-gnuradio] How to check if more input is available on an input stream

[Eric Blossom]

On Wed, Jan 07, 2009 at 02:38:34PM -0600, Mir Ali wrote:
> Hi Eric,
> 
> I actually forgot to mention one more thing.
> 
> I use N items of first stream and one item on second stream to produce N
> items on output stream.
> I am actually spreading data. If the spreading code is N-character bytes
> long, then each bit of data input byte (i.e. a total of 8 bits on input byte
> on second stream) will produce 8*N output items.
> 
> The input to the spreading stream is uninterrupted from a sequence generator
> block. But the input to the data stream i.e. the second input stream can be
> from a file which will exhaust when file is read completely. So i want to
> check if any data is available on the second stream(i.e. the data stream) in
> the work function each time i am done with the previous data byte.
> 
> I hope i make myself clear. Sorry for the confusion earlier.
> 
> Thanks
> Ali


OK, no problem.  Try this:



static const int N = 8;


my_new_block::my_new_block() : ...
{
  ...
  set_output_multiple(N);
  ...
}


void
my_new_block::forecast(int noutput_items, gr_vector_int &ninput_items_required)
{
  ninput_items_required[0] = noutput_items;
  ninput_items_required[1] = noutput_items / N;
}

void f(float *out, const float *a, const float *b)
{
 // write out[0] through out[N-1] using using inputs a[0] through a[N-1] and 
b[0]
 ...
}

int
my_new_block::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 *in0 = (const float *)input_items[0];
 const float *in1 = (const float *)input_items[1];
 float *out = (float *)output_items[0];

 assert(noutput_items % N == 0);

 for (int i = 0; i < noutput_items; i += N){

   f(&out[i], &in0[i], &in1[i/N]);

 }

 consume(0, noutput_items);
 consume(1, noutput_items / N);

 return noutput_items;
}


Note that there's no need to "check for input".  That's what forecast
does for you.  general_work won't be called until everything is OK.
You will have enough input to compute noutput_items.

Eric