Hi Marcus, > Gesendet: Freitag, 13. März 2020 um 13:29 Uhr > Von: "Marcus D. Leech" <[email protected]> > An: "Lukas Haase" <[email protected]>, "Rob Kossler" <[email protected]> > Cc: "[email protected]" <[email protected]> > Betreff: Re: [USRP-users] USRP X310 ignored DSP retuning on TX when using a > timed command > > On 03/13/2020 10:52 AM, Lukas Haase wrote: > > Hi again Rob, > > > > Yes, I confirm: > > > > 1.) Finally I get the commands to execute at the same time (TX and RX > > individually and both at the same time) > > 2.) Yes, the phase is random after each retune, even when I retune back to > > the same frequency > > 3.) (2) is only true if it includes *DSP* retuning. With naalog retuning > > (+integer-N retuning) I get phase coherence, as expected. > > > > I actually expected the PLL retuning much more challenging than the DSP > > retuning but for some reason it seems to be the opposite... > It depends on whether the phase-accumulator in the DSP is reset to zero, > or whether just the increment register is updated with the > new phase increment. There are good arguments for both approaches.
I just wanted to check in again if you know how this is implemented and how your thoughts are regarding tuning in both cases. My take: Case #1: Phase accumulator and increment register is reset. - This results in transients when re-tuning frequency because the mixer LO always (re-)starts at zero phase. - Since this completely defines the state of the DDC/DUC, I imagine phase coherence must be preserved assuming the resets in TX and RX happen exactly at the same time (which is still not certain to me) Case #2: Only increment register is updated - This results in a smooth transition - I would guess that this is what USRP implements - Since not the whole state of DUC/DDC is reset I can imagine there is a potential for phase coherence problems. - if I update the phase increment register for DUC to fdsp=500e3 and the phase increment register for DDC to fdsp=-500e3 can there be any way of breaking phase coherence? I just can't think of a away (because while the frequency is different, it's exactly the mirror frequency and results in the same absolut value) Thanks, Lukas _______________________________________________ USRP-users mailing list [email protected] http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
