[mythtv-users] My Perennial Problems with XvMC

chris at cpr.homelinux.net chris at cpr.homelinux.net
Wed Sep 20 03:37:15 UTC 2006

On Tue, Sep 19, 2006 at 08:05:31PM -0600, Norm Dugas wrote:
> I would check to make sure it's not a bus issue or a shared IRQ issue
> (if you've got AGP and PCI, don't know about PCIe).  Mobo docs should
> say something about IRQ assignments.  As for the bus issue, google would
> be my friend.

Note that almost all motherboards physically share IRQ lines 
between different PCI slots and the mobo resources, so often the 
only way to put two devices onto different interrupts is to 
physically move the card to a different slot.  Changing the IRQ 
assignment for one card won't have any effect as the other will 
follow it.

For example, on my Asus P4X8X-X the IRQ line assignments are:
IRQ C = PCI3 + mobo audio
IRQ D = PCI1 + PCI4 + mobo ethernet

The manual for the mobo mentioned that the AGP slot uses the same 
IRQ as PCI2 and PCI6, but the IRQ used by the on-board ethernet 
port wasn't mentioned *anywhere*.  I only found out about it when I 
bought a PCI IDE adaptor card and installed it in slot 4.  I had no 
problems until I started doing MythTV playbacks to a remote 
frontend.  When I did that, the ethernet port and IDE adaptor both 
started hammering the same IRQ line.  Eventually the system would 
get confused (the kernel watchdog would report an eth0 timeout and 
then the IDE driver would report that the drive had failed) and 
although the system didn't actually crash, it fell into an 
error/retry/error loop that prevented it from doing anything else.

Once I moved the IDE adaptor to a different slot the problem went 

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