Forum: GNU Radio framer_sink_1 and message queues

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578b0cee20f9985b3787b7e41ce05729?d=identicon&s=25 Paul Miller (Guest)
on 2008-11-18 17:20
(Received via mailing list)
[DISCLAIMER: I'm messing around in the 10011 svn trunk, so I expect
certain things don't work.]

I was playing with the message queues, trying to really figure them
out.  I wrote something that goes to files like this:

    topb = gr.top_block()
    modu = blks2.gmsk_mod()
    pktb = blks2.mod_pkts( modulator=modu )
    file = gr.file_sink(gr.sizeof_gr_complex, "test.dat")
    topb.connect(pktb, file)

And pull things back out like this:

    topb = gr.top_block()
    file = gr.file_source(gr.sizeof_gr_complex, "test.dat", False)
    modu = blks2.gmsk_demod()
    pktb = blks2.demod_pkts( demodulator=modu, callback=rx, threshold=12
    topb.connect(file, pktb)

Question 1:  Notice that I send_pkt("")?  It seems the last message
never gets de-queued (ever); which also happens with the svn ofdm
stuff apparently.  So I send a blank message before the eof.  Is that
a bug? or is that just a quark of the flow graph setup?

I'm trying to get this working without a modulator, not for any
practical reasons, but just understand a little better
(hopefully).  I'm queuing the messages this way (which I pretty much
ripped out of

class my_top_block(gr.top_block):
    def __init__(self):

        self._ac = packet_utils.default_access_code
        self.src = gr.message_source(gr.sizeof_char, 2)
        self.snk = gr.file_sink(gr.sizeof_char, "test.dat")

        self.connect(self.src, self.snk)

    def send(self,payload):
        pkt = packet_utils.make_packet(payload, 2, 1, self._ac, True, 0)
        msg = gr.message_from_string(pkt)

    def eof(self):

And I'm grabbing them back out of the file this way:

class my_top_block(gr.top_block):
    def __init__(self):

        self._ac         = packet_utils.default_access_code
        self.src         = gr.file_source(gr.sizeof_char, "test.dat",
        self.pktq        = gr.msg_queue()
        self.correlator  = gr.correlate_access_code_bb(self._ac, 12)
        self.framer_sink = gr.framer_sink_1(self.pktq)

        self.connect(self.src, self.correlator, self.framer_sink)

def main():
    tb = my_top_block()

    print "going to try to read a message from the file"
    msg = tb.pktq.delete_head()
    ok, payload = packet_utils.unmake_packet(msg.to_string(),
    print "%r %s" % (ok, payload)

I ripped the thread watcher stuff out of also, but it was clear
to me that delete_head() wasn't ever returning before program exit, so
I moved that to main() and ditched the thread watcher things
altogether.  I have added a file sink right after the correlator and
confirmed that the bytes definitely pass through it.  With or without
threads, delete_head() never returns, meaning (I think) that my packet
queue never receives messages from the correlator.

Question 2:  Why does the packet queue receive correlated messages
correctly in, but not in my simpler flow graph with no
modulator?  I'm clearly missing something really simple, but I've
spent enough time on it to know I'm not going to figure it out easily.

If riding in an airplane is flying, then riding in a boat is swimming.
107 jumps, 43.5 minutes of freefall, 83.4 freefall miles.
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