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

[Matt Johnston]

On Sun, Nov 21, 2004 at 01:27:15PM +0800, David Basden wrote:
> Hi guys,
> 
> Does anyone know much about how SVGA cards work?
> 
> Specifically, i'm wondering if I can use the RAMDAC in a boring
> SVGA card as an output for a software defined radio. 
> 
> People have been doing this for a long time with soundcards
> (I played with this for a while, and it's pretty easy to generate
> moderately low bandwidth stuff, such as AFSK1200, DTMF or Slow Scan
> TV. You just generate a buffer with a modulated sine wave[0] in it
> and throw it at your friendly local sound driver.[1])

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...

I'm fairly sure more recently someone actually put some more
developed software on the web somewhere to play a tune.
Though I can't seem to find it (will google a bit more
later).

> 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?


> 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?

Sounds like something fun to play with though :)

Matt