AsyncMsgSource

import numpy
import pmt
from gnuradio import gr

class AsyncMsgSourceC(gr.sync_block):
    """
    Transmits zeros when no messages in queue
    and their payload (complex samples) when present.
    """
    def __init__(self):
        gr.sync_block.__init__(self,
            name="async_msg_source_c",
            in_sig=None,
            out_sig=[numpy.complex64])

        self.ready_samples = numpy.empty((0,))

        self.message_port_register_in(pmt.intern('pdus'))
        self.set_msg_handler(pmt.intern('pdus'), self.msg_handler)

    def msg_handler(self, msg):

        pdu = pmt.cdr(msg)
        new_samples = pmt.to_python(pdu)

        self.ready_samples = numpy.concatenate((
                                self.ready_samples,
                                new_samples
                             ))

    def work(self, input_items, output_items):
        out = output_items[0]

        n_demanded = len(out)
        n_ready    = len(self.ready_samples)

        n_zeros = max(0, n_demanded - n_ready)
        zeros = numpy.zeros(n_zeros)

        n_consumed = max(0, min(n_ready, n_demanded))
        samples = self.ready_samples[0:n_consumed]

        out[0:n_consumed] = samples
        out[n_consumed:]  = zeros

        self.ready_samples = self.ready_samples[n_consumed:]

        # TODO: add sob/eob tags

        return n_demanded