How to reconfigure the parameters of top_block after it start runnig

Dear all,

I’m developing a transmitter in python, using USRP1 with LFTX plug-in
under GNU Radio3.2.

I’m wondering how to reconfigure some of the parameters of top_block,
while the flow graph has been running. How can I dynamically alter some
of the parameters of top_block every 1 second, while it is running. (in
my case the parameters that I would like to change are amplitude and the
frequency).

I really appreciate any of your help!

Thanks,
Yan

The top_block is built as:

class tx_bpsk_block(gr.top_block):
def init (self, subdev_spec,freq,verbose,chip_rate,amplitude):
gr.top_block.init(self,“tx_mpsk”)
self._freq = freq
self._verbose = verbose
self._amplitude = amplitude
self._u =
usrp_sink_s(0,subdev_spec,chip_rate,self._freq,self._verbose)
self.in_data = gr.message_source(gr.sizeof_char,14)
self.msgqq = self.in_data.msgq()
self._constellation = [-1,1]
self._mapper = gr.chunks_to_symbols_bf(self._constellation)
self._gain = gr.multiply_const_ff(self._amplitude)
self.f2s = gr.float_to_short()
self.connect(self.in_data,self._mapper,self._gain,self.f2s,self._u)

In main() the parameters set by user promt:
top_block = tx_bpsk_block(options.tx_subdev_spec,options.freq,
options.verbose, options.chip_rate,options.amplitude)
try:
top_block.start()
start_flag = 1
payload_13barker =
‘\x01\x01\x01\x01\x01\x00\x00\x01\x01\x00\x01\x00\x01’
while (start_flag == 1)
msg_13bit = gr.message_from_string(payload_13barker)
top_block.msgq.insert_tail(msg_13bit)
eof_msg = gr.message(1)
top_block.msgq.insert_tail(eof_msg)
# Amplitude and frequency suppose to be altered here
time.sleep(1)
# amplitude and frequency suppose to be altered again
top_block.wait()
except KeyboardInterrupt:
pass

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