Re: [Discuss-gnuradio] Maximum input items consumed on each input stream

[Ron Economos]

If you use set_output_multiple(), you don't have to check the input buffer. The block will only execute if there are a multiple of the value used in set_output_multiple() items available. For example, if set_output_multiple() is set to 256, the block will only execute if noutput_items is at least 256, but it could also be 512, 768, 1024, 1280, 1536, etc.

Since forecast() sets ninput_items_required to noutput_items, the same number of items appears on the input buffer.

Here's a dummy block that just copies input to output to show the structure. The loop in general_work() allows for any value of CHUNK_SIZE to work properly. With a size of 8900, the loop will typically only execute once.

#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include <gnuradio/io_signature.h>
#include <stdio.h>
#include "buffer_cc_impl.h"

#define CHUNK_SIZE 8900

namespace gr {
  namespace laura {

    buffer_cc::sptr
    buffer_cc::make()
    {
      return gnuradio::get_initial_sptr
        (new buffer_cc_impl());
    }

    /*
     * The private constructor
     */
    buffer_cc_impl::buffer_cc_impl()
      : gr::block("buffer_cc",
              gr::io_signature::make(1, 1, sizeof(gr_complex)),
              gr::io_signature::make(1, 1, sizeof(gr_complex)))
    {
      set_output_multiple(CHUNK_SIZE);
    }

    /*
     * Our virtual destructor.
     */
    buffer_cc_impl::~buffer_cc_impl()
    {
    }

    void
    buffer_cc_impl::forecast (int noutput_items, gr_vector_int &ninput_items_required)
    {
      ninput_items_required[0] = noutput_items;
    }

    int
    buffer_cc_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 gr_complex *in = (const gr_complex *) input_items[0];
      gr_complex *out = (gr_complex *) output_items[0];

      printf("noutput_items = %d\n", noutput_items);
      for (int i = 0; i < noutput_items; i += CHUNK_SIZE) {
        memcpy(out, in, CHUNK_SIZE * sizeof(gr_complex));
        in += CHUNK_SIZE;
        out += CHUNK_SIZE;
      }

      consume_each (noutput_items);

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

  } /* namespace laura */
} /* namespace gr */

Ron

On 8/30/19 15:58, Laura Arjona wrote:

Thank you very much Marcus, Michael, Abin, and Ron, really appreciate your responses.

To give some context, I just started designing a prototype reader to implement a custom protocol for backscatter neural implants; very excited to build my platform with GNU-radio :)

After reading all the information from your responses and links provided, I still have a problem with my implementation. According to the buffer sizes that you mentioned, I should not have this problem, but

I think I am missing something. I may need to re-design my system/flow-graph, but I would like to get a last advice/help, if possible. Thanks in advance!

I want my block Decoder to consume_each(>8900) but I get overflows "D" messages. See details below

I have 2  general out of tree blocks: Gate and Decoder.

They both have:

                ninput_items_required[0] = noutput_items;

                const gr_complex *in = (const gr_complex *) input_items[0];
                gr_complex *out = (gr_complex *) output_items[0];  

The flow-graph looks like uhd_source -> fir_filter_ccc -> Gate -> Decoder -> other blocks.   (Using a USRP N210 + SBX)

The idea is that I want the block Decoder to only process the input samples when I have received k samples. Let's set k=~8900

So, at the Decoder block general_work(), I set  consume_each(0) until ninput_items[0]>=k.

Basically, at the Decoder general_work() I have the following (just a overview, not pseudo-code):

 if (ninput_items[0] <k)

       //do nothing

      //consume_each(0)

else

     // process the input samples

     //consume_each(k)

My problem is that if I set k~8900, I get 'D' messages on the terminal.

And one interesting? thing happens. When ninput_items[0] gets close to k=8500 (or higher value), is when I start getting  'D', and after

that ninput_items[0] = 800, no matter the value of k.

Thank you.

Cheers

Laura.

On Fri, Aug 30, 2019 at 7:29 AM Müller, Marcus (CEL) <address@hidden> wrote:

Hi Ron,

just because I think this might be interesting to people dealing with
really high rates:
The maximum size is typically limited by the size of mmap'able memory
that you can allocate; that depends on the circular buffer factory
used:
For the posix shared memory thing, I don't think anything is stopping
you from using "memory space size" order amounts of buffer.
For anonymous file-backed mmap'ed buffers, I'd expect that we haven't
addressed the possibility of using more than 32 bit addresses, so
somewhere around 2 GB you'd find your upper limit.

Best regards,
Marcus

On Fri, 2019-08-30 at 06:20 -0700, Ron Economos wrote:
> Just to put a number on this question, the DVB-T2 transmitter uses up to 16 Megabyte buffers between blocks. I'm not sure what the absolute maximum is, but 16 Megabytes should cover most applications.
> The DVB-T2 blocks use set_output_multiple() in conjunction with forecast() to allocate these large buffers.
> Ron
> On 8/28/19 11:46, Laura Arjona wrote:
> > Hello GNURadio community,
> >
> > Does anyone know what is the maximum number of input items that an Out Of Tree block can consume on each input stream?
> >
> > consume_each(consumed) --> what is the maximum value that the variable consumed can take?
> >
> > Thank you very much.
> >
> >
> > --
> > Laura Arjona
> > Washington Research Foundation Innovation Postdoctoral Fellow in Neuroengineering
> >
> > Paul G. Allen School of Computer Science & Engineering
> > 185 E Stevens Way NE
> > University of Washington
> > Seattle, WA 98195-2350
> >
> >
> > _______________________________________________
> > Discuss-gnuradio mailing list
> > address@hidden
> > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
>
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--

Laura Arjona 

Washington Research Foundation Innovation Postdoctoral Fellow in Neuroengineering

Paul G. Allen School of Computer Science & Engineering

185 E Stevens Way NE

University of Washington

Seattle, WA 98195-2350