I have a general work function for which I will use GNU Radio’s history
functionality. In the block’s constructor, I call set_history( m ). I
cast
the input buffer in the standard way:
const float *in = (const float *) input_items[0];
My question is wheere in[0] refers to in the buffer. It would make sense
to
me that noutput_items is the number of new items for the block to
consume
and ninput_items[0] refers to the total number of data in the buffer.
So,
in[noutput_items-1] is the last element of the array, in[0] is the start
of
the new items, and the in[-m] refers to the beginning of the history
block.
Thus, ninput_items[0] is greater than or equal to m + noutput_items.
I don’t know if this assumption is true and would be pleased if someone
knew
how this works. The GNU Radio API is somewhat vague in this respect.
Thanks
in advance!
I have a general work function for which I will use GNU Radio’s history
functionality. In the block’s constructor, I call set_history( m ). I
cast
the input buffer in the standard way:
const float *in = (const float *) input_items[0];
My question is wheere in[0] refers to in the buffer. It would make sense
to
me that noutput_items is the number of new items for the block to
consume
and ninput_items[0] refers to the total number of data in the buffer.
So,
in[noutput_items-1] is the last element of the array, in[0] is the start
of
the new items, and the in[-m] refers to the beginning of the history
block.
Thus, ninput_items[0] is greater than or equal to m + noutput_items.
I don’t know if this assumption is true and would be pleased if someone
knew
how this works. The GNU Radio API is somewhat vague in this respect.
Thanks
in advance!
From you description you should use sync block.
Anyway, my knowledge on history is: (assuming 1:1 in-out ratio)
in[0] to in[noutput_items+m-2] are what you can use to produce
noutput_items outputs.
in[0] is the oldest and in[noutput_items+m-2] is the newest sample.
ninput_items[0]==noutput_items+m-1
me that noutput_items is the number of new items for the block to consume
KZ
Kyle,
Yes, that’s how the set_history works. Basically, when told you have
noutput_items, you know that you have noutput_items+(history()-1). The
default for set_history(m) is m=1, so that’s where the -1 comes from.
It allows you to look beyond the number of items you’ve been given.
It just needed a type cast in there. My code works now. The suggestion
about
gr_quadrature_demod_cf is very helpful; this will be a good reference
moving
forward on this project. Many thanks
I have a follow-up question about how history works in gnuradio. Making
no
assumptions about the input/output ratio of a gr_block, is it safe to
assume
that noutput_items is the number of new data given to the block? I.e.,
Does
calling ‘consume(noutput_items)’ consume all the new data available when
the
work function is called? If this is is the case, what does ninput_items
represent?
By default, yes, an input will have at least noutput_items available
to it. This is due to the forecast function that defaults to say that
the required number of inputs is the number of outputs plus the
history. So unless you overload the forecast function, this is how it
works.
When you say consume(i, noutput_items), then you are just telling the
scheduler that that is how many items read from the input. But there
could be more items available; you just (probably) wouldn’t process
them because you don’t have the space on the output.