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Re: [Discuss-gnuradio] Can the io signatur of the gnuradio blocks be dyn

From: Alex Zhang
Subject: Re: [Discuss-gnuradio] Can the io signatur of the gnuradio blocks be dynamically updated?
Date: Fri, 12 Oct 2012 11:39:04 -0500

Hi Tom, thanks for the response, but I am still have questions regarding your comments as below inline:

On Fri, Oct 12, 2012 at 10:12 AM, Tom Rondeau <address@hidden> wrote:
On Thu, Oct 11, 2012 at 7:41 PM, Alex Zhang <address@hidden> wrote:
> Let me take an example for my question.
> For some OFDM blocks, the io signature is determined by the fft length,
> during the constructing the block. However, sometimes, we need to adjust the
> the fft length dynamically based on some physical environment or computing
> environment.

Hi Alex,

I haven't thought about this too much, so my recollection of how
things work could be a bit off. But I'm pretty sure that the answer is
no, you cannot dynamically adjust this. You'd be messing too much with
the scheduler.

The way that you can do it is to lock the flowgraph, swap out the
block in question with a new block that has the new parameters, and
unlock to restart the graph. But you are going to lose samples in the
buffers into the block that you're removing.

This would actually be a great case for the event stream scheduler.
You could have different processing graphs that are selected based on
the state that you need. So you could populate graphs of different FFT
lengths and then dynamically select the right graph based on an event
when you detect a different length is required. This is still a
work-in-progress: https://github.com/osh/gr-eventstream.

It seems that the event stream scheduler can only handle finite options for selection?
This is different with what I am expecting. Sometimes, you don't know the actual options and the dynamic parameters is computed based on some other optimization algorithm. Thus I can not pre-configure finite graphs for my selection, but just adjust the exiting graph with specified parameter.

BTW, maybe my expectation is kind of over-design which brings more risk than benefits. But from the Software defined radio perspective, the dynamic/adaptive signal processing chain with expecting flexibility really deserves  more attention.

> On Thu, Oct 11, 2012 at 6:29 PM, Alex Zhang <address@hidden> wrote:
>> Hi,
>> I know it may not be possible in the current gnuradio blocks framework,
>> but I am still curious if it can be done.
>> When I write a signal processing block, the io signature could be
>> determined by some parameters. It is ok, if these parameters are fixed. But
>> sometimes, especially in the adaptive system, I need to dynamically update
>> these parameter, which result in the updating of io signature of the blocks.
>> I can make the io_signature to be independent with the dynamic parameters,
>> but it could be more convenient if the io signature can be adapted. Of
>> course, it is not easy, as the io signature change could impact the upstream
>> and downstream.
>> Thanks,
>> --
>> Alex,
>> Dreams can come true – just believe.
> --
> Alex,
> Dreams can come true – just believe.
> _______________________________________________
> Discuss-gnuradio mailing list
> address@hidden
> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio


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