Re: [Discuss-gnuradio] [SOLVED] Clock Recovery MM

[Robert McGwier]

Ooops.   Good catch Bastian.

On Fri, Sep 26, 2014 at 2:29 PM, Tom Rondeau <address@hidden> wrote:

On Tue, Sep 9, 2014 at 3:21 PM, Bastian Bloessl <address@hidden> wrote:

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

Just to follow up, Bastian was correct and we merged his patch in this week.

Tom

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Bob McGwier
Co-Owner and Technical Director, Federated Wireless, LLC

Professor Virginia Tech

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