[mythtv-users] Nova-T - Lots of recording errors with new Motherboard

Martin Smith martin at spamcop.net
Tue Apr 20 12:59:00 EDT 2004


I just upgraded my Myth system to an Athlon 2800+ with 333MHz bus and a new
KT600 based motherboard and transferred it to a neat black case to sit under
the TV in place of my now surplus VCR and DVD player.

I immediately noticed that I was getting many more stream problems on DVB
recordings than I used to. It was regularly coming up with "no data from card
in 1 second' followed by 5-10 seconds of messages while the continuity counter
sorted itself out. This initially happened every 5 minutes or so.

I spent a few fun hours yesterday playing with PCI latency settings and the PCI
DMA3 burst / threshold settings used by the dvb-kernel driver for the budget
SAA7146 cards and I was able to significantly reduce though not eliminate the
corruption.

As I have two DVB cards in the system I was then able to change the module load
order to make the other card #0 as seen by Myth. I then did 2 hours of
recording and didn't see a single stream error.

So there's definitely something wrong with this system. The initial candidate is
the IRQ sharing. The card giving problems is sharing with the AGP card. The one
that works is sharing with the ethernet adapter. I'll probably try moving it to
another slot next time I open the machine up.

I definitely found that playing with PCI latency helped matters. I'll probably
put something about this into my DVB document at the next update.

In terms of hardware choices this kind of problem may point towards boards with
an APIC. These tend to be the more expensive ones but have more available
interrupts.

Also the chipset choice is known to be a factor from several discussions on the
linux dvb driver list. Some of them react very badly to the PCI DMA parameters
that the dvb driver uses.

Martin


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