Re: [Discuss-gnuradio] question on implementing a state machine

[Martin Braun]

On 06/08/2015 07:16 PM, Anil Kumar Yerrapragada wrote:
> I am trying to implement a state machine based synchronization
> algorithm. The 2 states being "search for synch sequence" and "pass data
> through". 
> 
> As far as I can see, the ideal way to do this is to have the work
> function check what state it is in before proceeding. If it is in search
> state, the work function will search for the synch sequence and once
> found, switch to "pass data" and get out.
> 
> Next time work is called (use forecast to make sure that the number of
> input items available matches the amount I have data I have after the
> synch sequence), it will pass data through. Switch state back to
> "search" and so on.

FYI, the header/payload demux block does just that. It's pretty generic,
so it'll catch more cases than you need, but have a look at its source code.
> 
> My questions are these:
> 
> 1. Before each work call, does GNURadio automatically know the state
> that I left it in in the previous call? (Am I allowed to make work
> return anything else apart from len(output_items)?

No, but class attribute will persist between work calls.

> 
> 2. Is it better/possible to implement a separate block for the state
> machine that can somehow make the system aware of what state it is in?

Just make the state a class variable / attribute.

Have fun and good luck,

M