Re: [Discuss-gnuradio] Python block help

[Marcus Müller]

Hi Zach,

sorry it took me so long to react:
so, let's dissect a few things:

First, the general purposes of these functions:

* forecast() is called by the *scheduler* to ask your block "hey, if I'd
need you to produce N items, how much would you need on your 0. (and 1.,
and 2.,… if existing) input for that?". The scheduler usually repeatedly
calls that with a decreasing N until the number of samples your block
requires can be fulfilled by the number of input items that the
scheduler has ready. If that never happens, usually, something is broken.

* consume() is something that *you* call from within a (general_)work()
to signal the scheduler how many items you've consumed from the input(s).

* produce() is something that *you* call from within a (general_)work()
to signal the scheduler how many items you've put into the output
buffer. *If* you use produce, you should return the magic
WORK_CALLED_PRODUCE values. You usually don't call produce() – you just
return the number of consumed samples instead.

* noutput_items is **not** a variable that you set – it's the info how
many items you are asked to produce (parameter to forecast()) or how
many items you're **allowed at most** to produce (when it's the
parameter to a (general_)work())

Again, the better parts of your mail have been broken by Nabble. Abandon
Nabble. Subscribe directly:

https://lists.gnu.org/mailman/listinfo/discuss-gnuradio

Hope that helps,
Marcus

On 05/26/2017 07:49 PM, Zach Morris wrote:
> That worked to create a general block, but I'm still having some trouble with
> implementing the forecast(), consume() and produce() functions. 
>
> The goal of the block is to discard elements in an input vector that are
> below a certain threshold, and eventually update some statistics based on
> the remaining elements. For a vector of 256 elements, there could be
> anywhere between 0 and 256 outputs (the arbitrary ratio you mentioned).
>
> The default forecast function has a 1:1 ratio:
>
> Should I replace "noutput_items" with my "vector_length" parameter, ensuring
> that we always get (for example) 256 inputs?
>
> In the general_work function, I think we want to consume the entire input
> vector once we figure out which elements are above the threshold:
>
> I'm not sure about the produce function; do I need to tell the system how
> many items I produce, or is that covered at the end of general_work:
>
>
> Thank you kindly,
>
> Zach
>
>
>
>
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