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Re: [Discuss-gnuradio] fixing gr_pll_*_c[cf]
From: |
Eric Blossom |
Subject: |
Re: [Discuss-gnuradio] fixing gr_pll_*_c[cf] |
Date: |
Wed, 22 Mar 2006 13:32:32 -0800 |
User-agent: |
Mutt/1.5.9i |
On Wed, Mar 22, 2006 at 04:14:36PM -0500, Charles Swiger wrote:
> On Thu, 2006-03-16 at 14:39 -0800, Eric Blossom wrote:
> > On Thu, Mar 16, 2006 at 05:24:26PM -0500, Charles Swiger wrote:
> > > On Thu, 2006-03-16 at 12:35 -0800, Eric Blossom wrote:
> > >
> > >
> > > Here's the only place they're used:
> > >
> > > d_freq = d_freq + d_beta * error;
> > > d_phase = mod_2pi(d_phase + d_freq + d_alpha * error);
> > >
> > > It's way over my head but is d_freq supposed to be in the d_phase
> > > calculation, 2nd line? phase is mod_2pi but freq can be a very big
> > > number, like mod_2pi(100000 + 1.572849). That is I'm USING very big
> > > numbers for max_freq and min_freq - don't suppose they're normalized
> > > somehow.
> >
> > OK. I can see why that would be a problem. mod_2pi is optimized for
> > the expected "close in case" (symmetric around zero), thus the phase
> > isn't *really* getting folded down to [-pi,pi].
> >
> > Try changing mod_2pi to make the bounds check and then compute the
> > modulus if it needs to using division, floor, multiplication and
> > subtraction. It's not cheap, but it'll probably compute the right
> > answer.
>
> Does anybody know how to fix this in c++ ?
Chuck,
It's not broken. I was wrong. The "problem" is the lack of
documentation on what *any* of the arguments mean. In fact, the freq
args are in radians/sample. Thus it will always fall in +/- pi
and the existing code will keep it in range.
freq_in_hz * 2 * pi / sample_rate_in_hz --> radians/sample
Matt, will you *please* add doxygen comments to gr_pll_*.h?
Thanks,
Eric
- Re: [Discuss-gnuradio] pll_refout_cc - finding optimum alpha & beta ??, (continued)
- Re: [Discuss-gnuradio] pll_refout_cc - finding optimum alpha & beta ??, Eric Blossom, 2006/03/17
- Re: [Discuss-gnuradio] pll_refout_cc - finding optimum alpha & beta ??, Charles Swiger, 2006/03/17
- Re: [Discuss-gnuradio] pll_refout_cc - finding optimum alpha & beta ??, Charles Swiger, 2006/03/17
- Re: [Discuss-gnuradio] pll_refout_cc - finding optimum alpha & beta ??, ldoolitt, 2006/03/17
- Re: [Discuss-gnuradio] pll_refout_cc - finding optimum alpha & beta ??, Eric Blossom, 2006/03/17
- Re: [Discuss-gnuradio] pll_refout_cc - finding optimum alpha & beta ??, Charles Swiger, 2006/03/17
- Re: [Discuss-gnuradio] pll_refout_cc - finding optimum alpha & beta ??, Matt Ettus, 2006/03/17
- Re: [Discuss-gnuradio] pll_refout_cc - finding optimum alpha & beta ??, Robert McGwier, 2006/03/17
- Re: [Discuss-gnuradio] pll_refout_cc - finding optimum alpha & beta ??, Eric Blossom, 2006/03/20
- Re: [Discuss-gnuradio] fixing gr_pll_*_c[cf], Charles Swiger, 2006/03/22
- Re: [Discuss-gnuradio] fixing gr_pll_*_c[cf],
Eric Blossom <=