Re: Having problems using forecast method

[Martin Luelf]

Dear George,

what specifically does not work with your test? Any error messages, or 
is it not producing the result you are expecting. And if so, what is 
your block input, what is the output and what output are you expecting?

Keep in mind that the forecast method tells the scheduler how much input 
you *likely* need. This is not binding, meaning the general_work method 
does not have to produce this number of outputs, nor does GNURadio have 
to give you that exact amount of input data. In the general_work method 
you need to tell the scheduler how many samples you used (using the 
consume method) and how many samples you created (by returning that number).

Also be aware of the data types in C++. noutput_items is an int. If M 
and N are integer types as well, C++ will round M/N to the nearest 
integer before multiplying it to noutput_items and you have effectively 
created an integer decimating block. To avoid that you want to cast M, N 
and noutput_items to a floating point number type (if you know the C++ 
specifics you can probably get away with just casting one type and have 
the compiler cast the others, but just to be sure I would cast them all 
to float). With that you will get a floating point number of samples 
that your block needs. Since GNURadio can only deal with an integer 
number of samples, it is up to you and your algorithm to bring that to a 
sensible integer number. Most likely you will want to round that number 
up or down and feed this integer number of samples back into 
ninput_items_required[0].

Yours
Martin


On 05.07.21 22:51, George Edwards wrote:
> Hello,
>
> I played with it and got it to work. I left out the forecast method and 
> forced my will on the scheduler in terms of the input to output 
> sample relationship.
>
> However, I am still open to hearing from anyone who has used the general 
> block with the forecast method to solve this problem, so as to have the 
> perspective on how to use the forecast method.
>
> Thanks!
>
> George
>
> On Mon, Jul 5, 2021 at 2:44 PM George Edwards <gedwards.eng@gmail.com 
> <mailto:gedwards.eng@gmail.com>> wrote:
>
>     Good afternoon GNURadio community!
>
>     I am having a problem using the forecast method in my OOT model.
>
>     In my model, I have one input port and one output port with
>     streaming data. My signal processing algorithm converts every M
>     input samples into N output samples where the ratio of M to N is a
>     floating point number, soI cannot use the sync  block (if M=N) nor
>     the interpolator or decimator OOT blocks.
>
>     I am forced to use the general or basic block which has theforecast
>     method where one has to inform the Scheduler of the relationship
>     between the input and output samples.
>
>     In the forecast method, I set up the relationship as:
>     ninput_items_required[i] = noutput_items*M/N
>     which is the precise relationship. However, on running the QA test I
>     cannot get the OOT module to work properly.
>
>     Will appreciate any suggestions!
>
>     Regards,
>     George