[Discuss-gnuradio] Plumbing questions

[Marcus Leech]

I'm trying to morph wxgui/fftsink.py into a "strip chart" type sink for 
RA use.

I have most of the logic implemented (at least for a first experimental 
pass).

But I have questions about the appropriate plumbing.  I'm going to 
assume that
 the sink will be available only in float, with essentially no 
processing of the
 incoming data stream other than displaying it appropriately.

The following piece of "plumbing" from class fft_sink_f in fftsink.py 
confuses me:

       s2p = gr.serial_to_parallel(gr.sizeof_float, fft_size)
       one_in_n = gr.keep_one_in_n(gr.sizeof_float * fft_size,
                                   max(1, 
int(sample_rate/fft_size/fft_rate)))
       fft = gr.fft_vfc(fft_size, True, True)
       c2mag = gr.complex_to_mag(fft_size)
       self.avg = gr.single_pole_iir_filter_ff(1.0, fft_size)
       log = gr.nlog10_ff(20, fft_size, -20*math.log10(fft_size))
       sink = gr.message_sink(gr.sizeof_float * fft_size, self.msgq, True)

       fg.connect (s2p, one_in_n, fft, c2mag, self.avg, log, sink)
       gr.hier_block.__init__(self, fg, s2p, sink)

Functionally, I understand what it's doing, but I don't know what 
gr.hier_block.__init__(self,fg,s2p,sink) is
 all about.  I think that for my purposes, all I need to do is to 
lash-in a gr.message_sink to pass data events
 to the plotting routine.  That's the very last item in the fftsink 
chain--the gr.message_sink.

I think all I need to do instead of the above is:

      sink = gr.message_sink(gr.sizeof_float * 1, self.msgq, True)
      fg.connect(sink)

But what do I do with gr.hier_block.__init__(self, fg, s2p, sink)  ???