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Re: [Discuss-gnuradio] Analysis_filterbank
From: |
Eric Blossom |
Subject: |
Re: [Discuss-gnuradio] Analysis_filterbank |
Date: |
Tue, 13 Jan 2009 11:06:33 -0800 |
User-agent: |
Mutt/1.5.18 (2008-05-17) |
On Tue, Jan 13, 2009 at 08:45:43PM +0200, Sebastiaan Heunis wrote:
> Hi
>
> I think I have found what might be my problem with the
> analysis_filterbank. When using it as a polyphase channeliser, you
> need to start feeding samples in from the bottom channel, upwards.
> The gr.analysis_filterbank uses gr.stream_to_streams to split the
> input into a number of streams starting at the top. For a polyphase
> channeliser, this should be the other way round. I guess I need to
> make a different version of stream_to_streams to do this. Can someone
> please just help me with some c++ code? In particular the work()
> function of gr_stream_to_streams:
Sebastian, I think you're confused about what's going on.
Even if the output is backwards (I'm not convinced), you can just
rewire the output with connect. No reason to code a block.
> const char *in = (const char *) input_items[0];
> char **outv = (char **) &output_items[0];
> int nstreams = output_items.size();
>
> for (int i = 0; i < noutput_items; i++){
> for (int j = 0; j < nstreams; j++){
> memcpy(outv[j], in, item_size);
> outv[j] += item_size;
> in += item_size;
> }
> }
>
> Firstly, why do we use a pointer to a pointer for the output data?
Uhh, because it's the correct type?
Look at the type of output_items. It's
gr_vector_void_star &output_items
which is a typedef (gr_types.h) for
std::vector<void *>
There's a distinct pointer for each output stream. The code writes N
output streams.
Eric
> For what I intend to do, I need to do the following, right?
> memcpy(outv[nstreams-j-1],in,item_size);
> outv[nstreams-j-1] -= item_size; //or out[nstreams-j-1] += item_size?
> in += item_size;
>
> Thanks
> Sebastiaan