[LAU] wireless and realtime?

Ken Restivo ken at restivo.org
Mon Jan 28 18:08:10 EST 2008

On Mon, Jan 28, 2008 at 12:20:46PM -0800, Jon H wrote:
> Hey all,
> I've been having problems trying to find a realtime kernel that has
> decent wireless support.  I tried JAD 1.0, which performed quite
> nicely, but did not have adequate wireless support or even madwifi
> "out of the box", which I apparently need.  I'm running a D-Link
> DA-2320 PCI card which uses the Atheros chipset (madwifi?) and when I
> inquired about it on their forums it didn't seem to take much
> priority.  I think 64Studio also struggled with this card but it's
> about the only chipset locally available that has any track record at
> all with linux.  This card IS quite nicely supported under Ubuntu and
> family "out of the box" but the kernel supplied with UbuntuStudio,
> while it handles my wireless nicely, is more sluggish, in regards to
> latency, than the vanilla Ubuntu kernel.
> I'm not afraid to try building a kernel for myself, just wondering why
> so many realtime kernels seem to lack the proper wifi support that IS
> available to linux in general?  I also seem to remember reading
> somewhere some problem with certain wifi drivers co-existing with a
> stack or something needed for realtime?

My guess would be either licensing, or the legwork required to dig around for the drivers, or dealing with reliability (or lack thereof).

The drivers for my rtl-based wifi USB cards are very flaky and just barely usable, and available either from the manufacturer or from random project websites (not built in to the mainstream kernel). Also, there is a confusing mish-mash of competing, duplicated drivers and forks. It's a mess. If I were distributing a kernel there is no way I'd include them.

The good news is, I was able to build and test nearly all of the drivers for my USB wifi cards without having to recompile the kernel at all! The source packages build them as .ko modules outside of the kernel source tree. One of them even came with a nice hacky shell-script to copy the drivers over to /lib/modules/`uname -r`/kernel/drivers for me.


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