Tue, 15 Feb 2000 Marc Le Roy wrote:
> I need to generate images in real time at frequencies up to 75 Hz, and
> if possible synchronized with the frame synchro of the PCI SVGA graphics
> board.
Does that mean you need to control the frame rate of the video card accurately?
(You have to do that if you need a rock solid, smooth and flicker-free display.)
If so, you probably have to program the timing of the video card manually. Any
decent X server lets you do that - you just have to make sure you end up with
V/H frequencies and sync timing that the monitor can handle.
> 1) Is it possible to use RT-linux for this purpose ?
Uhm, well, you could port svgalib or something (the new kernel graphics console
stuff?) to RTL (which means; turn it into a kernel driver), but I doubt that
that should be required...
> 2) Which software library :
> - compatible with RT-Linux (i.e. usable from kernel modules)
There's no such thing really, not even kernel drivers - as long as you need
"RTL class" hard real time all the way through.
> - using accelerated functions of the SVGA adapter,
> should I use in order to avoid to re-develop basic 2D primitives ?
I'd go with X if it can do the job. Some alternatives available; proprietary
ones with accelerated support for the latest and hottest hardware if you need.
Most of the interesting cards are well supported by XFree86, though.
If you can do with millisecond accurate scheduling guarantees (keep in mind
that a frame at 75 Hz is some 13 ms!), the new lowlatency patches should do.
Test data:
http://www.gardena.net/benno/linux/audio/
HOWTO:
http://matrix.crosswinds.net/~linuxmusic/lowlatency.html
However, IIRC, a normal X server doesn't like being run as SCHED_FIFO in a
normal setup... It might be possible to sort it out if only one application
(another SCHED_FIFO app) is using it. Running KDE + some apps with X as a real
time task can easily result in a system freeze... (As any real time
applications can, BTW! If you want to debug in a safer environment, or need
fault tolerance, you should use high priority watchdog tasks, or better, a
hardware watchdog that can trigger an interrupt that kills off all RT tasks, or
a similar solution.)
Regards,
//David
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