Re: [Discuss-gnuradio] gr_message_sink

[seph 004]

--- Eric Blossom <address@hidden> wrote:

> On Sun, Oct 07, 2007 at 04:09:48PM -0700, seph 004
> wrote:
> > I was wondering if someone could perhaps clarify
> how the  gr_message_sink works . I'm trying to make
> a modified version of the  fft_sink. I noticed that
> the sample stream is turned into a vector  streasm
> and then sent to a message sink.
> >   
> 
> >  When the data is unpacked from the messages, then
> it seems there
> >  are a varying number of fft frames in each
> message. How does this
> >  happen? Why isn't there only one frame per
> message?
> 
> It builds a message that contains however many items
> were handed it by
> work.  It could be changed such that each item was
> placed into it's
> own message, but that didn't seem to make sense. 
> Consider what would
> happen if the items were floats.
> 
> >  Also, what exactly are msg.arg(1) and msg.arg(2).
> Are they part of
> >  the message payload or part a special frame?
> Lastly, what does
> >  self.msgq.delete_head() do?
> 
> >   Regards
> >   Lance
> 
> See:
> 
>  
>
http://gnuradio.org/doc/doxygen/classgr__msg__queue.html
>  
>
http://gnuradio.org/doc/doxygen/classgr__message.html
>  
>
http://gnuradio.org/doc/doxygen/classgr__message__sink.html
> 
> 
> A quick look at the source:
> 
> int
> gr_message_sink::work(int noutput_items,
>                     gr_vector_const_void_star &input_items,
>                     gr_vector_void_star &output_items)
> {
>   const char *in = (const char *) input_items[0];
> 
>   // if we'd block, drop the data on the floor and
> say everything is OK
>   if (d_dont_block && d_msgq->full_p())
>     return noutput_items;
> 
>   // build a message to hold whatever we've got
>   gr_message_sptr msg = gr_make_message(0,            // msg
> type
>                                       d_itemsize,     // arg1 for other end
>                                       noutput_items,  // arg2 for other end
> (redundant)
>                                       noutput_items * d_itemsize);   // len 
> of msg
>   memcpy(msg->msg(), in, noutput_items *
> d_itemsize);
> 
>   d_msgq->handle(msg);                // send it
> 
>   return noutput_items;
> }
> 
> 
> Eric
> 

Thanks for those links. I think I understand what is
happening a bit better now.

I was wondering if there is a way to align messages,
or at least, the samples within the messages. I made
some changes to the fpga code to insert a particular
sample pattern into the receive sample stream. 

What I'd like to do is only plot a certain number of
samples that follow on after the sample pattern. This
lead me to the fft sink which also plots sets of
samples at a time, but not aligned to any particular
point. 

Are there changes I could make at the python level to
plot samples relative to a particular pattern?

Regards

Lance 




       
____________________________________________________________________________________
Yahoo! oneSearch: Finally, mobile search 
that gives answers, not web links. 
http://mobile.yahoo.com/mobileweb/onesearch?refer=1ONXIC