No sharing IRQ broken board problem

No sharing IRQ broken board problem

[tcrix]

I have a pci board in development that works but..
it can not share the interrupt line.  

Has someone hacked through the problem of reserving one of the inta, intb, .. 's for a single device?  I would love to see how you did so I could continue on with my driver while I wait for the !@$#!@ hardware guys to fix the board. 

Thanks for the help,
Tom Rix

Re: No sharing IRQ broken board problem

[Lennart Sorensen]

On Wed, Nov 02, 2005 at 09:06:53PM +0000, tcrix@att.net wrote:
> I have a pci board in development that works but..
> it can not share the interrupt line.  
> 
> Has someone hacked through the problem of reserving one of the inta, intb, .. 's for a single device?  I would love to see how you did so I could continue on with my driver while I wait for the !@$#!@ hardware guys to fix the board. 

As far as I understand the PCI specs, your device is currently NOT a PCI
device.

Support for shared IRQs on PCI is as far as I can tell not optional.
Short of designing your own mainboard there is no way to prevent the
interrupt lines from being joined.  One one board I use there are 6 PCI
devices, with 3 on INT-A and 3 on INT-B (The SBC doesn't have INT-C and
INT-D).  On my desktop machine, INT A is the same on slot 1 and 5, 2,
and 6 and onyl 3 and 4 have INT-A to themselves.  Of course this doesn't
prevent the bios from assigning the same IRQ to INT-A on multiple sets
as well.  I have run a PPro some years ago with a single IRQ shared
among all the PCI devices in the system.  Neither linux nor windows had
a problem with that and neither did any of the many PCI devices.

I think you are stuck waiting for the hardware guys to give you a PCI
device that is really a PCI device.  If you are lucky you can find one
slot in your machine that doesn't share INT-A with any other PCI device,
although on most modern machines there are so many PCI devices that it
is imposible to find one that isn't shared.

Len Sorensen

Re: No sharing IRQ broken board problem

[linux-os (Dick Johnson)]

On Wed, 2 Nov 2005 tcrix@att.net wrote:

> I have a pci board in development that works but..
> it can not share the interrupt line.
>

It's on the PCI bus. It needs to be an "open collector" type.
Sharing or not is really not a software issue! The only
kind of hardware problem that could cause "shared interrupt"
line problems is the designer fails to provide the correct
kind of interface driver. In that case, just "dead-bug" a
FET (or two) on the board, near the connector, to convert
the driven bit to an open-collector (drain) bit.

> Has someone hacked through the problem of reserving one of the inta, intb,
> .. 's for a single device?  I would love to see how you did so I could
> continue on with my driver while I wait for the !@$#!@ hardware guys to fix
> the board.
>
> Thanks for the help,
> Tom Rix
> -

Cheers,
Dick Johnson
Penguin : Linux version 2.6.13.4 on an i686 machine (5589.55 BogoMips).
Warning : 98.36% of all statistics are fiction.
.

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