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
On Wed, Jan 7, 2009 at 12:37 PM, Eric Blossom <e...@comsec.com> wrote:
> On Wed, Jan 07, 2009 at 04:44:39AM -0600, Mir Ali wrote:
> > Hi,
> > I have a simple question. I have a block that has 2 input streams and the
> > inputs are consumed at different rates. For each 1 input consumed on the
> > first input stream N inputs are consumed in the second stream.
> >
> > The forecast function and set_multiple call of this block are as shown
> > below,
> >
> > my_new_block::forecast(int noutput_items,gr_vector_int
> > &ninput_items_required){
> > assert(noutput_items % N==0); # the
> >
> >
> > int items_on_first_input_stream = noutput_items;
> > int items_on_second_input_stream = noutput_items/(8*N);
> > ninput_items_required[0]=items_on_first_input_stream;
> > ninput_items_required[1]=items_on_data_input_stream;
> > }
> >
> >
> > {
> > set_output_multiple(8*N); # the output items are a multiple of
> 8*N.
> > }
>
> > For each (8*N) inputs consumed on second stream 1 input is consumed on
> first
> > stream.
> > If the first stream has uninterrupted supply but the second one doesn't
> then
> > how should I check if input is available on the second stream. Will the
> > input_vector contain NULL values when nothing is in it? If it is true
> should
> > i just do
> >
> > if(second_stream[next_item]==null){
> > .......
> > }
> >
> > Please clarify.
> >
> > Thanks
> > Ali
>
> You should be deriving your class from gr_block (you may already be doing
> this).
> There is no need to call set_output_multiple.
>
> If I understand you correctly, to produce a single output item, you
> need a single item on the first input stream, and N (== 8) items on the
> second stream.
>
> Assuming I'm understanding you correctly, then your forecast routine
> should be:
>
>
> static const int N = 8;
>
> 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;
> }
>
> You then need to override general_work, not work:
>
> (I'm assuming that your input and output types are float. Change as
> required)
>
>
> float f(const float *a, const float *b)
> {
> // Produce a single float value by using a[0] and b[0] through b[N-1]...
>
> return XXX;
> }
>
> 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];
>
> for (int i = 0; i < noutput_items; i++){
>
> out[i] = f(&in0[i], &in1[i * N]);
>
> }
>
> consume(0, noutput_items);
> consume(1, noutput_items * N);
>
> return noutput_items;
> }
>
>
> Eric
>
--
Mir Murtuza Ali
Graduate Student
Center for Wireless Communications
University of Mississippi
University, MS 38677
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