Re: [Discuss-gnuradio] Rearranging a running flow graph

[Josh Blum]

Patrick Strasser wrote:
> Hello!
>
> I'd like to construct a demo for grc which can switch between two or 
> more branches in a flow graph, like AM or FM: given a Signal, this 
> would be modulated by an FM and an AM branch, then one is selected for 
> a simulated channel (noise) and afterwards the signal is fed to either 
> a FM or a AM demodulator. I want easily switch between the two 
> behaviours, but am not shure about how to do this the Right Way.
>
> I'd do this now with multiplicators, but that introduces for every 
> branch a new block, and keeps the unused paths running, which is 
> rousource hungry (I don't have that much CPU power).
A mute outputs zero when it is "muted", so this is as effective as the 
multiplier (maybe a bit faster). I did not integrate the mute because 
there is no way yet to use a variable/slider to control an enumerated 
data type like the mute parameter which is true or false. A multiply 
constant with a variable min=0, max=1, step=1 is the best solution at 
the moment.
> An other way would be to do disconnects and connects in the flow 
> graph. Is this a sensible way to go? Can I rearrange a running flow 
> graph or do I have to stop before rearranging and start the flow graph 
> afterwards?
> Josh: What do you think about integrating this into grc?

I did not know that one can disconnect blocks in a running flow graph. 
This is possible? Anyway, I will save that idea for the future.
> The third possibility would be contruct a swtich block that takes n 
> inputs and has a method to select the input by a number. Would this be 
> possible an a way so that the not-to be consumed path temporarily 
> discontinues processing? On continuation, the interrupted path would 
> work with old data. Any way to flush this or are the buffers small 
> enough to neglect this effect? I guess this would also be true for 
> connect/disconnect.

I think gnuradio needs a mux and a demux block. A mux has N inputs and a 
set_n method. The mux will only feed the output with the nth input 
stream (throw out/ignore the other inputs). A demux has N outputs and a 
set_n method. The demux will only feed the nth output with the input stream.

The mux seems easy to make. Is the demux possible in the current 
gnuradio? Meaning: can you feed one output and starve the other outputs?

In Patrick's example, the demux outputs would be an FM and an AM 
demodulator.
> Patrick
-Josh