Re: [RTnet-developers] Interrupt sharing realtime / non-realtime

[Jan K. <ki...@rt...>]

Klaus Keppler wrote:
> That's clear - but I wasn't sure if there's really a problem
> whith shared interrupts.
> 
> In the meantime I swapped my "new" NICs with some via-rhine based
> cards and experienced the same problem when sharing interrupts.
> (so I proved that there's no bug in my freshly ported driver...)
> 
> Concluding I can say that RTnet (+RTAI) can't be used on NICs
> which share their interrupt with non-realtime NICs (which are
> in use at the same time).
> 

The problem with sharing IRQ line between RT and non-rt drivers is that
the non-RT driver at least has to be given the chance to acknowledge and
switch off the IRQ source on its related device. Otherwise, the IRQ line
will remain active, shadowing any IRQ from the RT device.

I once made Philippe to add the required infrastructure to Adeos. It now
takes a specifically patched non-RT driver to register a real-time-safe
acknowledge handler with Adeos to quickly release the IRQ line again.
Not trivial.

The reason we once thought we need it was some nice PC104+ NIC which
shared the same IRQ line than the onboard NIC of the attached embedded
PC. As it finally turned out that we had to change some other jumper
than the one labelled with "IRQ No." to actually switch the line (really
a great piece of hardware...), we no longer had to solve it in software.

Jan