Re: [Discuss-gnuradio] gri_mmse_fir_interpolator_cc::interpolate returns NaN

[Kyle Zhou]

Tom Rondeau wrote:
> The error suggests that the d_mu value is < 0, which is unrelated to
> the inputs being all 0. There should be no problem with inputs being
> all 0, and if d_mu is less than 0, something is going wrong. Not sure
> what to tell you right now, but more debug information would be
> helpful.
>
> Tom
>
>   
Thanks Tom.
Yes, you are right. the error is unrelated to the inputs being all zeros.
Actually, d_mu is not negative either. d_mu is NaN when the error occurs.
By doing some debugging, I have located the problem in 
gr_fir_ccf_simd::filter(), which is called by 
gri_mmse_fir_interpolator_cc::interpolate(), which in turn is called by 
gr_mpsk_receiver_cc::general_work().
For the first call, gr_fir_ccf_simd::filter() returned a value with NaN 
as its imaginary part.
Then this value (interp_sample in gr_mpsk_receiver_cc) is passed into 
mm_error_tracking(), which causes mm_error, and particularly, d_mu to be 
NaN.
Then when gri_mmse_fir_interpolator_cc::interpolate() is called again 
with d_mu passed in, the first line
imu = (int) rint(mu*NSTEPS);
will produced a negative imu, which raises the assertion failure.

So the problem lies in gr_fir_ccf_simd::filter(). But why does it return 
NaN? I am not sure.
This only happens in Cygwin.

I put aside the problem and switched to Ubuntu to continue my work.

Strangely, after some time of augmenting my codes, when I return to 
Cygwin with the augmented codes, that problem disappeared secretly!

Now I cannot reproduce that problem, which prevents me from further 
debugging.

Kyle