RE: [Discuss-gnuradio] File format question

[Bahn William L Civ USAFA/DFCS]

Thanks, that helps some.

I figured that I could put in the literal size of the data, in bytes, but that 
only helps if it actually matches how the GR blocks are going to process those 
bytes.

When possible, I would prefer to use the constants that have been set up so 
that the code is (1) more readable, and (2) more maintainable. So instead of 
using "8" for complex, I would like to use gr.sizeof_"whatever". But I don't 
know what "whatever" needs to be. Where do I find this?

I'll look at dbpsk.py and tunnel.py when I get my Linux box set back up. Is 
there a module that takes time domain data and converts it to IQ pairs, or am I 
responsible for doing that when I generate the file? If so, what LO frequency 
would I need to use?

It would be so much simpler if I could just use the generated time domain data 
directly.

Thanks!

> -----Original Message-----
> From: Dan Halperin [mailto:address@hidden
> Sent: Tuesday, August 14, 2007 3:19 PM
> To: Bahn William L Civ USAFA/DFCS
> Cc: address@hidden
> Subject: Re: [Discuss-gnuradio] File format question
>
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> Bahn William L Civ USAFA/DFCS wrote:
> > I have a few questions, but they mostly come down to: What is the data
> file format when using a file as a signal source?
> >
>
> These file_sink and file_source are direct wrappers for the C functions
> fwrite and fread and behave exactly as they do. A file is therefore
> simply a binary containing {chars,shorts,ints,floats,etc} in
> local-endianness.
>
> > Question #1: What is the syntax for the itemsize argument?
> >
> > Since the example doesn't use one of the data types mentioned, it is
> hard to tell what the syntax is supposed to be. For instance, if I want to
> use gr_complex, do I specify gr.sizeof_gr_complex? If I want to use
> unsigned char, is it "gr_sizeof_unsigned_char" so as to eliminate the
> space?
> >
> > Question #2: What are all of the options for the itemsize argument?
> >
> > It lists "gr_complex", "float", and "unsigned char" yet the example uses
> one that is not in the list. Are there others?
> >
>
> Itemsize is the size, in bytes, of the object to be written. Valid
> useful values are 1 (char), 2 (short), 4 (int/float), 8 (complex);
> although I suspect you could put anything fwrite/fread accepted in there
> and it would work.
>
> > Question #3: Does the data file format for transmitting match the data
> file format when receiving?
> >
> > Can I take a file that is recorded, say using receive_file_c.py (may not
> have the file name exactly correct) and use that as a source without
> modification? If so, what does it mean to use IQ pairs as input data? What
> does the USRP do with them?
> >
>
> Yes. When I'm working on building a receiver for a certain modulation
> scheme, for example, I transmit some data and run usrp_rx_cfile.py on
> the receiver, then use a gr.file_source block as input to my receiver
> blocks to allow for reproducible testing without polluting the airwaves.
>
> Similarly, you could if you wanted generate a file to transmit by using
> a file_sink instead of a usrp_sink and then send it across the USRP with
> a file_source -> usrp_sink.
>
> The I/Q pairs are processed by the USRP from files the same way they are
> from a normal GNU Radio block such as e.g. the DBPSK modulator (see
> dbpsk.py, tunnel.py).
>
> - -Dan
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