[linux-dvb] Re: packet loss DVB-ip

[Ralph Metzler <rjkm@metzlerbros.de>]

Alexandre CONRAD writes:
 > >
 > >
 > >AFAIR, you had a full featured card. If that is correct than it is
 > >quite possible to have packet losses, because auf the limitations of
 > >the DEBI port that connects the card to the PC and the low speed of
 > >ARM CPU on the card. For high speed data connections it is usually
 > >better to use a budget card.
 > >
 > Yes, I am using a Nexus DVB-s. But I have the same problem using a nova 
 > card. Your brother Ralph was at Eutelsat Paris France last year to help 
 > me out on that. I needed to setup the cards and all, and I didn't know 
 > about satellite and linux. That's why we asked him to come. He has just 
 > setup the card to make it work. We didn't test packet loss with the 
 > open-sky application. But at this time of the year, I was testing with a 
 > Nova card, and I had exactly the same problem (with 0.9.4 drivers).

Regarding the packet loss problem I wrote back to Eutelsat later on last
year after I implemented the fix in the fidbirq routine which
eliminated packet loss problems (at least for one other who reported
it, see mailing list archive in May 2002).
The 0.9.4 drivers (they are from late 2001) of course never had that fix.
That fix originally only was in the old CVS at Convergence and later our
drivers at www.metzlerbros.de. 

You might have read about the fiddling around in the IRQ routine 
during the last few weeks. Maybe you have more luck with one of those.
Some don't make much sense (i.e. they do not fix the original
problem). The one using the VPE interrupt sounds most promising but 
I did not try it myself yet.


 > >How high is your data rate?
 > >
 > "How low" you mean. We rent a dedicated 256kb/s rate from eutelsat for 
 > sending our file around. Not that high.

How high is the data rate on the PID you use? 
I mean the complete PID, not just your part.


 > Do you know what this is ? While I'm sending data (or a little after the 
 > data is received) my PC crashes, blinking leds, and all... (sorry for 
 > posting this again).
 > 
 > [...]
 > [<d88dc664>] StartHWFilter [dvb-ttpci] 0xd4
 > [<d88a1db9>] dvb_net_filter_set [dvb-core] 0x360

Yes, that bug is known.
set_multicast_list() in network drivers is called during IRQ.
The sleeping in calls to the ARM causes the crash.
The cleanest way to solve this would be by using the interruptible 
work queues of the newer 2.5.x kernels.
AFAIK, in 2.4.x there is only one interruptible task queue which is
shared with all other processes. Maybe here a "network multicast 
filter setting thread" would be better.

Btw., this bug also can occur in other drivers, since functions
in dvb_sw_demux.c can go to sleep when waiting for a semaphore.
 

Ralph




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