[mythtv] "Strange Error Flushing Buffer" problem

Harondel J. Sibble mythtv-dev@snowman.net
Tue, 17 Dec 2002 16:21:24 -0800

On 17 Dec 2002 at 18:37, Richard Bowman wrote:

> I guess I've just got this computer too maxed out. I truly thought once
> we got rid of ISA slots that IRQ problems weren't an issue. Windows
BUAHAHAHAHAHA!  When pigs fly. About the only option is a good dual processor 
board or a good single processor board with an APIC that supports more than 
16 interrupts.  They do exist but aren't exactly easy to find.  The other 
problem is that regardless of the number of irq's you have, most boards have 
pci slots running on the same INT (ie hard coded to the same irq), so as 
another poster mentioned, the agp slot and the pci slot beside it usually 
share an irq amd typically the the 5 or 6th slot shares irq's with the usb 
controllers or with another slot. In some strange cases the 6pci slot doesn't 
seem to be able to get an irq at all.  Once you have more than 4 pic slots 
you can count on more irq sharing.

Typically you want to place your higher priority cards (ie high i/o bandwidth 
using) in the lower numbered pci slots, most motherboards have the highest 
priority slot closest to the agp slot.  So in my case with a fully loaded 
system, I have agp video card, scsi card, dxr3 (mpeg decoder), tv tuner1, 
nic, sound card, and tv tuner2. Note for a number of reasons this would 
normally be a suboptimal setup, but based on the cards I have, it's what 
seems to work best under both linux and windows. Normally I'd have the sound 
card in the lowest priority slot, but due to case constraints, I had to swap 
spots with one of the tuners.

> seems to reassign devices to IRQs much higher in number than the first
> 15. I thought I'd seen Linux do this as well in its bootup, but I don't
> seeing remember RedHat 8 doing it, which I have now.
Probably you have one of those boards with the aforementioned APIC's.  Linux 
does have support for that, try googling for "mps 1.4"

> I'm going to update the MB's BIOS, so I can hopefully have a bit more
> control over the IRQ's.
Most reasonably modern boards will give you control over the irq's on a slot 
by slot basis, however, you'll typically only be able to assign irq's to the 
first 4 pci slots (the other slots will be slaved off the first 4 or will 
share irq's with the first 4 or other pci devices like usb). Some high end 
workstation boards and server boards allow assigning a different irq to every 
slot even when you have 6 or more pci slots.

Harondel J. Sibble 
Sibble Computer Consulting
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