Re: PCI/IRQ hardware question

Robert Moonen is a darn nice person I don't care what anybody says!
>
> Kernel irq sharing in no way implies hardware irq sharing capabilities.
>
Perhaps it is a matter of my wording, say,  share as in process, or share as 
in bed.. My initial search led me to correspondence between kernel hackers 
but the excerpts below from an email on another list at another time seems to 
imply the same sort of thing in a more understandable way.
<snip>
What happens when cards are sharing interrupts is that when the
interrupt is received, the kernel queries each driver that is using the
interrupt, basically asking "Was that your interrupt?". The driver in
turn reads the appropriate register on it's PCI card to determine
whether it was the one, and responds accordingly. When the device is
found, the interrupt service routine for it is executed. Pretty simple,
and when used correctly it works quite well. And the vast majority of
cards and drivers out there do use it correctly.
<snip>
Sorry, not true. Only one interrupt can be serviced at a time (if you
only have one processor), but that is the case regardless of whether or
not the interrupt is shared.
<snip>
I agree that the Intel interrupt model is somewhat wacky. But I can
confidently predict that virtually everyone on this list is sharing
interrupts, without problems. In my case, my sound chip is sharing
interrupt 11 with the an ethernet card, and my video card is sharing
interrupt 10 with my other ethernet card.

If you only have one processor in your machine, it is only capable of
doing one thing at a time. But it sure seems like you can have many
tasks going simultaneously; my computer is engaged in SETI at the same
time I am typing this, with no apparent affect. And that is due to each
task being repeatedly interrupted, so fast that I cannot notice it. The
same is true for handling of other hardware interrupts.
<snip>
The complete email can be found here:
https://www.redhat.com/archives/redhat-list/2001-January/msg01857.html

.........

-- 
Cheers,

Rick Miles

Movement stopped is no movement,
and rest set in motion is no rest.

Written on Boomtime, the 64th of Discord, 3171 
http://www.members.optusnet.com.au/~rickfrm/