Re: [Discuss-gnuradio] Oscilloscope/FFT layout, data source, etc...

[Eric Blossom]

On Thu, Nov 30, 2006 at 12:15:59PM -0400, Ryan Seal wrote:
> I have been working on a wxWidget based oscilloscope/spectrum widget and 
> have a few questions:
> 
> First, let me cover my idea of an oscilloscope/FFT program:
> 
> 1. Data is provided from a source (USRP or file).

> 2. Data is formatted to fit the plotting window (transform matrix).
> 3. Data is sent to the plotting widget at specified intervals for display.


> I am a little confused as to how this should be handled when converted 
> to Python. I could write 2 or 3 classes and let the main plotting widget 
> handle the entire show; or I could break this up and a small Python 
> module would combine these objects separately. To me, I view this as a 
> "sinking" object and a single widget would provide everything.

Seems reasonable to me.  It's a sink, it accepts "records" (vectors)
of data and plots them.

> But I don't want to continue without some sort of feedback. At this
> point, I have a resizable window with ticks, a grid, and a few
> labels and have plotted some test data and am happy with the
> performance so far.

> A few more specific questions:
> 
> 1. Where/How do I access the USRP data stream (at the C++ level) and is 
> the data buffered in a way (P/C model) that allows me to know which 
> buffer is being filled and which one is ready to be read, overflows, 
> underflows, etc...?

Have you looked at
http://www.gnu.org/software/gnuradio/doc/howto-write-a-block.html

It spells out the basics of writing a new C++ block.

> 2. Is there a standard data type (at the C++ level) that I should be 
> using when loading/manipulating the data  ( valarray, vector, pointers, 
> gr_xxxxx, etc...)?

See howto-write-a-block.

> 3. Is wxWidgets pretty much the standard for GNURadio development?

It is at this point, but there are folks talking about Qt and/or PyQt.
I have yet to see any code ;)

> I have been looking around at other toolkits trying to find a good reason 
> to move from QT (for various reasons) and it appears that FLTK is 
> gaining momentum with other groups. Has anyone considered this? Or are 
> there compatibility reasons for not going this route?

Independent of the conversation about a move to Qt or not, we do need
a faster plot widget for wxPython.

> I am concerned with the C++ aspect of the USRP because I want to 
> integrate this card with my current system for use with radar (305-m 
> dish). I currently use another card (overpriced garbage IMHO) that dumps 
> blocks of data into shared memory (up to 40MBPS) and I can then run 
> multiple processes capable of processing, storing, viewing data in 
> real-time. I should be able to replace the current digital receiver card 
> with the USRP (assuming I modify the FPGA to provide a triggered mode) 
> and dump this data in a similar manner.

Sounds doable.

I'm not sure that I really answered your questions.  If I missed the
mark, please ask again.

Eric