The "in" buffer should start at in[0] the history comes into play at allowing
enough valid indices to perform the filtering operation over the entire buffer
which allows N valid output data versus N-nTAPS. When I looked at filtering in
gnuradio the way I thought about it as and at the end I've included some ASCII
art to demonstrate it, from the illustration you can see how the history comes
into play. I'm no DSP engineer but this seems to work for me someone can feel
free to correct me if I'm wrong.
< adapted from gr_fir_fff_generic.cc>
for(i=0; i<n; i++)
for(j=0; j< ntaps; j++)
out[i] += taps[j] * input[i+j]
0 1 2 3 4 5 6 7 8 9
hist0 hist1 hist2 hist3 in0 in1 in2 in3 in4 in5
tap3 tap2 tap1 tap0
0 1 2 3 4 5 6 7 8 9
hist0 hist1 hist2 hist3 in0 in1 in2 in3 in4 in5
tap3 tap2 tap1 tap0
0 1 2 3 4 5 6 7 8 9
hist0 hist1 hist2 hist3 in0 in1 in2 in3 in4 in5
tap3 tap2 tap1 tap0
0 1 2 3 4 5 6 7 8 9
hist0 hist1 hist2 hist3 in0 in1 in2 in3 in4 in5
tap3 tap2 tap1 tap0
0 1 2 3 4 5 6 7 8 9
hist0 hist1 hist2 hist3 in0 in1 in2 in3 in4 in5
tap3 tap2 tap1 tap0
0 1 2 3 4 5 6 7 8 9
hist0 hist1 hist2 hist3 in0 in1 in2 in3 in4 in5
tap3 tap2 tap1 tap0
0 1 2 3 4 5 6 7 8 9
hist0 hist1 hist2 hist3 in0 in1 in2 in3 in4 in5
tap3 tap2 tap1 tap0
al fayez
-----Original Message-----
From: Josh Blum <j...@joshknows.com>
To: Discuss-gnuradio <Discuss-gnuradio@gnu.org>
Sent: Sun, Sep 25, 2011 6:59 pm
Subject: [Discuss-gnuradio] making gnuradio blocks entirely in python
So there is a useful feature I think gnuradio is missing, and thats the
ability to rapidly prototype signal processing in python. It would be
great if a python block would have access to all the facilities
available to a block written in a c++ environment.
So I put together pyblock (not to be confused with those other project
by the same name). Its a stand-alone build that links against gnuradio.
https://github.com/guruofquality/pyblock
Theres a few demos: an adder, using tags, interp and decim blocks.
https://github.com/guruofquality/pyblock/tree/master/examples
The interesting thing is that the work functions just call into numpy
routines, so there is a chance that the implementations can be
reasonably fast.
I would like to be able to support history so i can implement a filter
using numpy but I am a little lacking in the basic understanding so fill
me in if you know. Suppose I have this work function:
int work(int noutput_items, gr_vector_const_void_star
&input_items,gr_vector_void_star &output_items){
const float *in = reinterpret_cast<const float *>(input_items[0]);
I am assuming history is on the input buffer.
Is the vector "in" ninput_items + history() items long? Where
ninput_items = noutput_items*/some_factor.
Whats the first index of the first item? Is in[0] or in[0-history()]?
-Josh
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