Re: [Discuss-gnuradio] Bug in gr_quadrature_demod_cf, or scheduler?

[Matt Ettus]

Steven Clark wrote:
> Thanks Matt, I understand the issue now and switching atan functions
> does indeed make the glitches go away.

Great!

> Do you have a sense of how much slower the regular atan2f function is
> than gr_fast_atan2f?

I think Eric looked at it a while ago when he wrote it.

> If the performance hit isn't too bad, I might leave it in for peace of
> mind.

You are dealing with very low sample rates, so I wouldn't worry about
the performance.

> What is the best strategy when you want to rx a signal at a very slow
> symbol rate? Max decimation (256?) on the USRP, then decimate/filter
> some more in software? As an arbitrary example, symbol rate 7812.5
> sym/sec: have the usrp decimate by 256 and you're still at 32
> samp/sym. What is the best way to partition decimation between hw and
> sw? Which sw blocks are ideal for this?

In general, decimate as much as possible in hardware, where it is free. 
However, I usually try leaving the last 2x (or more) for the software
decimator, which will have higher precision and better filter skirts. 

In software, use the standard gr_fir_filter blocks, and just set the
decimation rate (which is the first parameter, I think).

Matt