On Tue, Feb 06, 2001 at 07:58:00AM +0100, Bart Thissen wrote:
> "Daniel R. Schuette" wrote:
> >
> > My application is time critical so I would like to be able to use
> > RTLinux's hard IRQ capabilities. However, since I have a large number of
> > modules (six) on the CPCI bus there seems to always be a conflict between
> > one of my modules and an IRQ line used by a Linux (non-RT) device. This
> > creates a problem because my driver cannot service the Linux device's
> > interrupt and RTLinux won't release the interrupt since my driver has
> > registered a hard IRQ.
> >
> > The optimal sollution would to re-assign the IRQ lines so that there is no
> > conflict. Unfortunately though the BIOS my system is using (AWARD) does
> > not support this nor do I know of a way to do it in Linux.
> >
> There are only 4 interrupt lines on the PCI bus, which are shared between
> the 6 slots and the AGP bridge. I think it's best if you register your irq's
> as hard-irq and check in the handler if the irq is caused by a non-rt linux
> device. In that case you can raise a software-interrupt to pass it to linux.
> In that case the non-rt handler should be installed on this soft-irq.
The number of interrupts on the PCI bus depends on your motherboard
design. There are 4 interrupts _per slot_, which on typical older
motherboards are physically linked to 4 interrupt lines going into
the bus controller. However, this is not true on my alpha, which
links the 4 interrupts on 5 slots to 20 separate IRQs, nor on my
Tyan Tomcat II SMP motherboard, which links interrupt A on each
card to IRQs 16-20.
To answer the first question, if you are lucky enough to have an
IO-APIC on the motherboard, you can compile the Linux kernel in
SMP mode (for 2.2) or 'APIC support on UP' (for 2.4), and then
you can reassign IRQs as necessary at boot parameters. Otherwise,
you have to deal with a broken BIOS.
dave...
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