Hi,\
\
Some RFNoC blocks which process samples in in batches can require \`spp\` to be 
set to the batch size or a multiple/divider of it.\
\
To my knowledge the updated FFT block is one of them. At least the [example 
specifies that the SPP should evenly divide the FFT 
size](https://github.com/EttusResearch/uhd/blob/c354764c93b49c90be08958f942b9bcb7704cbd5/host/examples/python/fft_loopback.py#L577).

\
So depending on your FFT size, this would probably be my guess to why you are 
seeing issues when not setting \`spp\` according to this scheme.\
\
Regards,\
\
Niels

---

Nikos Balkanas wrote:

> Hi Zhou,
>
> Glad you were able to resolve your issue.
> Interesting...spp = 1024, has nothing to do with fosphor, but instead
> adjusts all I/O to the streamer.
> It is used to set maxsps (maximun samples per second) for your streamer.
> Errors to that generate
> a crash in your convert functions. What is your connection MTU? With 9000
> MTU you should get 1991 maxsps...
> Is your hardware, cable, card OK? Check uhd_rx_streamer_max_num_samps for
> more details.
>
> HTH
> Nikios
>
> On Tue, Jun 24, 2025 at 11:03 AM 
> [[email protected]](mailto:[email protected]) wrote:
>
> > I’ve resolved this issue. As it turns out, 'spp=1024' is necessary for the
> > ‘RFNoC RX Radio’ block. The correct yml and grc file are attached for
> > reference.
> >
> > ---
> >
> > USRP-users mailing list -- [email protected]
> > To unsubscribe send an email to [email protected]
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