On Thu, Sep 8, 2016 at 6:34 PM, Pavan Yedavalli <psy2...@columbia.edu>
wrote:
> My current flowgraph consists of a signal source (cosine) ->
> stream_to_vector of size 1024 -> forward FFT of size 1024 -> complex_to_mag
> of size 1024 -> file sink of size 1024 (unbuffered OFF and append set to
> overwrite).
>
> After I run this flowgraph for a few seconds and manually stop it, I use
> scipy.fromfile(open("filename"), dtype=scipy.float32) to retrieve the
> values from the binary file. However, the length of this output vector is
> some integer multiple of 1024 every time. Shouldn't it always be 1024
> because I'm overwriting the file? I noticed that the longer I run the
> flowgraph, the larger this value is, so it seems like it may not be
> overwriting? Or perhaps there is something else I need to do make sure that
> my output is always of length 1024 with just the magnitudes of each sample?
>
The Vec Length field on the file sink doesn't mean the size of file it
writes; it means the size of each stream item it writes (as a multiple of
the input type's size). In your case each stream item is 1024 floats, which
means exactly that your file will always contain some number of 1024-float
items, as you have observed.
There is nothing in GNU Radio that will repeatedly overwrite a file as the
flow graph runs — I suggest you find another way to accomplish your goal.
What were you planning to use to *read* this file?
(If you just want a single FFT, you can add the Head block in your flow
graph, set to 1, and the flow graph will exit after writing that one.)
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