Receiving data from 2 USRP daughterboards simultaneously based on benchmark_rx.py error

hi,
I want to use Rfx 400 and Rfx 2400 daughterboards on a usrp
simultaneously
to receive data from another usrp which has the same daughterboards.
The
transmit way use 2 daughterboard simultaneously is ok.
but in receiving path i got nothing but gr.fr_fir_ff:using sse. it does
not
call the rx_callback function.

I modified receive_path.py in these place:
1)usrp.source(nchan=2)
2)set.mux(0x32103210)
3)make 2 rx_callback functions
4)and many places must double to make two way receiving blocks

my connect block is:
self.packet_receiver0=
blks2.demod_pkts(self._demod_class(**demod_kwargs),
access_code=None,
callback=self._rx0_callback,
threshold=-1)
self.packet_receiver1=
blks2.demod_pkts(self._demod_class(**demod_kwargs),
access_code=None,
callback=self._rx1_callback,
threshold=-1)

di=gr.deinterleave(gr.sizeof_gr_complex)
self.connect( self.u, di )
self.connect( (di,0), self.chan0_filt, self.packet_receiver0 )
self.connect( (di,1), self.chan1_filt, self.packet_receiver1 )

i have no idea which part is wrong. the transmit path i modified in the
same
method is working well.
could anyone can help me?

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