[URC] Using a SVGA card as part of a direct synthesis SDR?

[David Basden]

On Mon, Nov 22, 2004 at 12:05:26PM +0800, Matt Johnston wrote:
> A while back (like, at high school writing stuff in visual
> basic) I made a little program to display things on the
> screen (a modulated sine-wave), alternating between two
> patterns, and on the radio nearby I managed to get it to
> produce a few tones (I assume it was AM). Of course it was
> fairly rough, I was ignoring the blanking etc, and wasn't
> exactly driving a proper antenna or anything...

Cool :)

> > Does anyone know if modern SVGA hardware is this flexible? Looking
> > at the XFree86 server, it seems to be so (given you can manually
> > specify timings and dotclocks). You even have megabytes of really
> > fast output buffer hooked into a speedy bus, while helpful people
> > have already put fast software pipelines in for graphics stuff.
> 
> I reckon the hardware itself can probably do it, though
> getting raw data into the video card might be harder.
> Filling the entire screen on-the-fly is probably a bit
> difficult (?) though perhaps if you worked with textures
> already mapped into videocard memory and switched between
> them it could be promising?

Getting the raw data to the card quickly is surprisingly easy if you use
an existing library, because GraphicsGeeks<tm> have already optimised
the software and hardware pipelines to do just that. This is assuming
that you can convince the library to switch off blanking etc.

> > This is, also, without looking at GPUs, which quite possibly could
> > do much of the modulation for you. They already do this with bitmap
> > images (stretching, mixing etc). Why not with a sine wave?
> 
> Yeah, could be a go. Though I guess there might be some
> issues with GPU transforms applying to an area on the
> screen, as opposed to radio sine waves where you want the
> transformations to be continuous wrapping around the screen?

I wonder if you could convince it that the framebuffer was 1
pixel high and very, very wide.

> Sounds like something fun to play with though :)

Yeah :)

David