[Nottingham] Odd request - drive multiple VGA

[Michael Simms]

On Tue, 2004-05-11 at 22:23, Michael wrote:
> I'm looking for some Linux-happy hardware to drive multiple VGA displays 
> from the same CPU -- quite specifically 30 VGA displays!!! I've had some 
> fun in recent years with Predator 4 & 8-head VGA cards but that was 
> purely Win32 - now I want to step it up somewhat and display individual 
> fullscreen raster images on 4 banks of 30 separate 800x600 TFT screens 
> (120 in total) controlled (or directed) from the same CPU or from 4 
> separate CPUs.
> 
> My first ideas are based on an array of multi-output PCI VGA cards - 
> however, these cards can be more costly that a cheap PC. So another 
> option is for a low-unit-cost local processor attached to each TFT 
> running a tiny distro whose sole job it is to display a fullscreen 
> framebuffer or X image as dictated by a server. The required update rate 
> is in the order of one static image every 10 seconds but all the screens 
> need to update promptly on demand and preferably in a particular sequence.
> 
> So, any thoughts out there?

Well, I would say if you are willing to have a CPU per screen, you could
just xhost a server and have a script to set the correct display and
then display the image on that remote X session. Easy as pie.

> Out of interest, what sort of bandwidth would remote X sessions demand 
> if the images are static?

Well, looking at it you have 800x600 images, you dont say what colour
depth but let us assume 24 bit for the sake of arguement, that gives us
an uncompressed size of

800*600*24

bits per screen, and you want 120 screens, so you have

800*600*24*120

bits per sequence, but you only want one sequence every 10 seconds, so
you are left with

800*600*24*120/10

With a sum bps of 138240000

Which is 131 Mbps, more than a standard 100baseT network could handle...

So you have gigabit ethernet coming out of the server, into 4 switches,
one for each bank. Each switch would be running at 131/4=33 Mbps which
is well within the capacity of a 100baseT switch.

1 gigabit ethernet card, 4 switches with 1 gigabit port and the rest
100baseT and you are set

Alternatively you could compress the information, send it down the
network and have the local machines do the display. It would require a
bit of coding to have them do it (unless there is an app Im not aware of
that does that job) but shouldnt be hard.

-- 
Michael Simms - CEO, Tux Games
http://www.tuxgames.com