See fir_filter_blok.impl.cc for an example ... forecast() does not include history. For a sync, interp or decim block, forecast is not required at all.
history() should be the number of previous items required, without the (-1). On Mon, Aug 28, 2023 at 5:08 AM Marco Menchise <marco.mench...@gmail.com> wrote: > Hi, I'm a gnuradio newbie. > > I'm trying to write a block that calculates output at time k based on > three input samples: one at time k-N-1 (in the past), one at time k (the > current sample) and one at k+M (in the future). > > I spent some hours struggling against "history" and forecast function. > > Here: > https://lists.gnu.org/archive/html/discuss-gnuradio/2016-04/msg00520.html > I found a good visualization of the history concept. As I said, I also > need to process "future" samples so I also investigated the "forecast" > function. > > Here is what I understood: > > 1) history=N tells the scheduler to prepend N-1 "old" samples to the > input_items buffer. The oldest prepended sample has relative index = 0, so > the "current" buffer starts at index N-1. > > 2) The forecast function must return N-1 + noutput_items+ M, where M is > the number of samples required in the future. Forecast *must* take into > account history. Each general_work call is guaranteed to have *at least* > N-1 + noutput_items+ M samples in input_items buffer. > > 3) I did some tests and noticed that the scheduler may pass to > general_work *more* than N-1+noutput_items+M samples. Extra samples should > be ignored by general_work. They will be passed again in the next call. > > 4) general_work must "consume" just noutput_items samples > > I tried to collect all those concepts in the attached figure where I used > both absolute and relative indexes to mark samples. I assumed history=4 and > M=2. The input_items in the first general_work call has at least 9 samples. > I must process input samples from 103 to 106 (included) using samples from > 100 to 108 (included) and I must generate 4 output_samples. In the next > call I must process samples from 107 to 110 (included) and, again, I must > generate 4 output samples. I must ignore "extra" samples in both cases. > > Is that correct? I'm I missing something? > > Thanks, > Marco > > > > > > [image: gnuradio.drawio (1).png] >
