[VxW] Re: Interrupt sharing and Vxworks-doubt-help plz!!!

karthik bala guru kbalaguru0 at yahoo.com
Wed Mar 24 21:06:33 PST 2004

Consider the following scenario :
There are just two threads in a process and nothing else.
What are the factors that will affect the threads performance ?
karthik bala guru

Sundararaman Shiva <shivavs at yahoo.com> wrote:
ssubba at blr.pin.philips.com (subbarayan) wrote in message news:<635cdb91.0403022127.630b1917 at posting.google.com>...
> Dear all,
> 1)What exactly is meant by interrupt sharing?
> 2)My understanding is 2 devices sharing the same interrupt pin.Is my
> understanding correct?If I am wrong can some one tell what exactly
> is wrong in my understanding?
> 3)If 2 devices share the same interrupt, on what basis will be the
> corresponding ISRs for the devices which are sharing the interrupt get
> invoked?
> 4)Becos till now i understood that one interrupt vector can be
> connected to only one ISR.so how to make one interrupt vector connect
> to 2 ISRs?
> 5)Does Vxworks support the above said scenario?
> 6)How to implement and handle such interrupt sharing in vxworks both
> in h/w level and s/w level?
> 7)what changes are to be done in vxworks files in bsp as well as
> configuration files for the above case?
> I use Vxworks5.4,tornado2.0,win2k host.x86 arch.Though I am in need of
> solution for my current configuration,it will be helpful if some one
> throws some light on my configuration and by default for other h/w
> archs also with regards to the above case.
> Expecting all ur replies and advanced thanks for the same,
> Regards,
> s.subbarayan

Interrupt sharing is when multiple devices share the same interrupt
pin. To know more about shared interrupts, the best place to look for
would be PCI devices. As far as I know, the PCI host bridge can handle
only 4 interrupts. Hence, multiple PCI devices share the interrupts.

When using shared interrupts, the normal scenario I would expect would
be to have the ISRs figure out who caused it. Hence, if an interrupt
from a shared interrupt pin occurs, all the related ISRs
(corresponding to devices sharing the pin) are made to execute
sequentially. The ISRs are expected to be intelligent enough to figure
out if the appropriate device caused the interrupt. This is how
pciIntConnect() functions. pciIntConnect merely creates a linked list
of ISRs that are sharing the same interrupt line. When the interrupt
occurs, it sequentially invokes all the ISRs connected to it.

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