[linux-dvb] Re: DVB, MythTV and PVR-350

[Hamish Moffatt <hamish@cloud.net.au>]

On Tue, Dec 21, 2004 at 10:38:12AM -0800, Florin Andrei wrote:
> On Tue, 2004-12-21 at 15:17 +0100, Jan wrote:
> > Am Montag, 20. Dezember 2004 08:21 schrieb Florin Andrei:
> > > Anyone here using a DVB card in conjunction with MythTV and a PVR-350?
> 
> > I am using a AverTV DVB-T 771 Card beside my PVR-350. I have a lot of trouble 
> > with the bt878 driver if both card running (recording). 
> > ...
> > Nov  7 14:17:16 localhost kernel: bt878(0): irq FBUS risc_pc=1e41a210
> > 
> > The result is a heavy damaged mpeg stream.
> 
> Wow, that's pretty bad.
> 
> If you take the DVB card off-line, then it's fine, right?
> Sounds like a driver issue to me...

IMHO it's due to the FIFO in the BT878 being too small for DVB data.
It's designed for audio but it's being run at up to 10x the data rate
to carry the MPEG2 transport stream. (Possibly more like 15x.)

The FIFO overflows because the card had to wait too long to get access
to the PCI bus. You may be able to improve the situation by fiddling
with the PCI latency timers (man setpci); probably by reducing the
counters on your OTHER cards, rather than doing anything for the A771 in
particular.

I have two DVB cards (one BT878, one not) and see this very
occasionally. No amount of latency tweaking has gotten rid of it
completely.

Hamish
-- 
Hamish Moffatt VK3SB <hamish@debian.org> <hamish@cloud.net.au>