Re: [Discuss-gnuradio] Clock Recovery MM

[Bastian Bloessl]

On 09 Sep 2014, at 15:42, Tom Rondeau <address@hidden> wrote:

> On Mon, Sep 8, 2014 at 5:49 PM, Bastian Bloessl <address@hidden> wrote:
> Hi all,
> 
> looking at the clock recovery MM code, I wonder if d_omega_relative_limit is 
> a relative or absolute deviation from d_omega.
> 
> Here it looks like absolute
> https://github.com/gnuradio/gnuradio/blob/next/gr-digital/lib/clock_recovery_mm_ff_impl.cc#L107
> 
> Here it is relative
> https://github.com/gnuradio/gnuradio/blob/next/gr-digital/lib/clock_recovery_mm_ff_impl.h#L57
> 
> (even though this code has no impact since d_{min,max}_omega is not used.)
> 
> 
> I don’t have access to the book linked in the docs atm.
> 
> Best,
> Bastian
> 
> 
> It is supposed to be relative. I'd have to verify the math on that line 107 
> in the .cc file, but it's supposed to adjust the center position of the 
> current omega estimate and then apply the clipping. Then it adds the mid 
> point back to get it back to where it's centered. Try walking through that 
> line one more time to verify that it's doing that properly. But yes, it's 
> supposed to be relative to the original setting of omega.
> 

So this line asserts that the current (absolute) deviation (d_mega - 
d_omega_mid) is smaller than the maximum allowed absolute deviation 
(d_omega_mid * d_omega_relative_limit). AFAIS, the second argument is missing 
“* d_omega_mid”.

I will create a patch, then you can check if I got you right.

Bastian