On Mon, Aug 28, 2023 at 1:08 PM Jeff Long <willco...@gmail.com> wrote:
> 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. > Sorry I can't find the code you pointed out. I saw this: https://github.com/n-west/gnuradio-volk/blob/master/gnuradio-runtime/python/gnuradio/gr/gateway.py I don't know what block is but it seems that default forecast implementation does include history. > history() should be the number of previous items required, without the > (-1). > If history=1 (default) there are no items prepended. So the number of prepended items should be history-1 This post https://lists.gnu.org/archive/html/discuss-gnuradio/2011-02/msg00480.html seems to state the same thing: "If you set the history to 'N', this means you always have the last (N-1) input values kept in your buffer." Am I wrong? Thanks, Marco > > 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] >> >
