[linux-dvb] Adjusting drivers for slow CPUs - buffer overruns suspected

Tim Hewett tghewett1 at onetel.com
Thu Mar 8 18:06:04 CET 2007

I am wondering if there are ways to adjust the DVB drivers to suit a  
slow CPU.

The background is that I have two Technisat SkyStar2 DVB-S cards in a  
PIII 550MHz PC. If I try to record an entire transport stream the  
recording suffers from drops and gaps, something which doesn't happen  
when recording one video and audio PID, presumably because their five  
hardware PID filters are doing the hard work.

Before upgrading to the 2.6 kernel (ages ago) the same PC would  
happily record an entire transport stream concurrently on each card  
without any data loss, so it doesn't seem as if the PC is  
fundamentally running out of steam. Something changed in the DVB  
drivers for the 2.6 kernel which started causing problems it seems.

Now I've added a Twinhan VP-1025, which has no hardware filters at  
all apparently, I'm getting data drops whether I record an entire  
transport stream or just one audio and video PID, I guess because the  
filtering is done in the CPU.

So I'm wondering if there are tweaks which I can make to the DVB  
drivers, maybe to increase buffer sizes, or some other adjustment, to  
try to stop these drops happening.

Any ideas?

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