--- Eric Blossom <[EMAIL PROTECTED]> 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
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