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Re: [Discuss-gnuradio] Clock Recovery MM
From: |
Bastian Bloessl |
Subject: |
Re: [Discuss-gnuradio] Clock Recovery MM |
Date: |
Tue, 9 Sep 2014 21:21:02 +0200 |
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