[Discuss-gnuradio] Problems with Mueller & Mueller clock recovery; not very reliable in my system

[Christian Sokolowski]

Hi,

I have some trouble using the function gr_clock_recovery_mm_cc.cc (Mueller & 
Mueller Clock recovery). Using DPSK with 
datarate 40 kbps, the communication system works perfect running a simulation 
without USRP board. The problem occurs when I switch to the board: when 
calling/initialising the receiver client of the system, in approximately 70% 
of the cases the following error message shows up. 

scipio:/home/cso/da # ./mdpsk_rx_rrc_client_thread.py
>>> gr_fir_ccf: using SSE
Using RX d'board A: Flex 400 Rx MIMO B
python: gri_mmse_fir_interpolator_cc.cc:66: gr_complex 
gri_mmse_fir_interpolator_cc::interpolate(const gr_complex*, float): 
Assertion `imu >= 0' failed.
Aborted

Once the clock is synchronised (the other 30% cases), the receiver works 
fine. The problem is 'temporarely' solved by unplugging the DC power supply 
of the board. Is it possible that some buffers on the hardware remain filled 
from former runs on the board?

I am calling the M&M clock recovery with the following parameters:
clock_sync = gr.clock_recovery_mm_cc(self.sw_decim, 0.25*0.009, 0.5, 0.03, 
0.002)


parts of gri_mmse_fir_interpolator_cc.cc, which is called by 
gr_clock_recovery_mm_cc.cc:

gr_complex
gri_mmse_fir_interpolator_cc::interpolate (const gr_complex input[], float mu)
{
  int   imu = (int) rint (mu * NSTEPS);

  assert (imu >= 0);
  assert (imu <= NSTEPS);

  gr_complex r = filters[imu]->filter (input);
  return r;
}

I expect that "assert(imu >=0);" is not very robust for synchronising the 
signal for some unknown reason.

thanks for any help.

Chris

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