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Re: re-synchronize data transmission when parameter changes


From: Marcus Müller
Subject: Re: re-synchronize data transmission when parameter changes
Date: Wed, 29 Sep 2021 19:11:58 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1

Hi Wei,

it sounds to me like a bit of an "esoteric" use to adjust the number of repetitions at runtime for a transmission, but that should not stop you!

Not all things can work, though:

>  For example, by asking the two repeat blocks always
> process the same amount of samples,

No, that's not how GNU Radio works!

> or each time I change the
> parameters, the two file sources re-transmit the file from the beginning
> simultaneously?

That wouldn't solve the fact that the repetition factor of your two "Repeat" blocks aren't set synchronously.

Instead:
If you want, you can:

Stream A -->|Streams to|               |Vector to|--->
Stream B -->|  Vector  |--->|repeat|-->| Streams |--->

By far the most elegant way would be if you wrote your own C++ repeat block that has an arbitrary number (instead of just 1) input (and the same number of outputs). Then, you could avoid the "Streams to vector" and "vector to streams" trickery.

Best regards,
Marcus

On 29/09/2021 18.10, Huang Wei wrote:
Hello everyone,

I am testing the transmission of the same signal in parallel through two repeat blocks (see attached flowgraph). The repeat times of both repeat blocks are set by the same GUI range from 2 to 10. When I start running the flowgraph, the two output signals are exactly the same as expected. But when I change the repeat times from the GUI range, the two signals are not synchronized anymore (see attached signal plot).

I am wondering, is there a way to keep the two signals always synchronized? For example, by asking the two repeat blocks always process the same amount of samples, or each time I change the parameters, the two file sources re-transmit the file from the beginning simultaneously?

I am doing this because I want to transmit the signals simultaneously through two synchronized USRPs, and I don't want the mis-match of the signals due to changing the parameter in the repeat blocks every time.

Appreciate if someone could help me!

Regards,
Wei


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