[linux-dvb] Re: distortions on P4 systems (12V hungry?)

["Stefan Betermieux" <stefan.betermieux@fernuni-hagen.de>]

> I think it is becoming very clear that the choice of PCI burst used by the
> budget driver is inappropriate for many chipsets, including common stuff
> like the i845, many via boards, and also the i865 (my Asus P4P800)

Yes, I can confirm this. Maybe we should gather some recommended values
and list them somewhere.

> That snippet you refer to gives advised values for a series of boards.
> However, in my case (asus P4P800) I had to go to zero to get any kind of
> stable transfer (I didn't try 2 & 4 DWords, but 16 and 32 were still
> unstable).  I assume that this is equivalent to switching off PCI bursting
> altogether?  Without a value of  in PCI_BT_V1 I was seeing very severe
> corruption of the mpeg stream (mplayer typically dies within 1-2 seconds)

I have used vdr the last months with this "anomaly", it didn't die, but it
had a choppy live stream. Tonight I have tried various combinations of
threshold and burst rates, and I get an almost perfect results with a 8
Dwords burst and a 4 Dwords threshold (i845 machine). The most sensitive
parameter is the threshold value, which unfortunately can only be lowered
to 4 Dwords.

> I would be happy to make the value a kernel module option?  Would this be
> accepted as a patch?  If so, would it need to be done against both the DVB
> and dvb_kernel branches?  Also, what would be the implications of changing
> the default to 0?  Is this going to be loading the PCI bus unneccessarily
> for other users?

I had the same idea, recompiling the kernel took too long. It is a very
small patch, I have posted it to the list in a new thread.
Changing the value to 0 made my situation worse. I suppose there will be
no one-value-fits-all solution.

> Your other question, does the budget card use only DMA channel 3?  Yes I
> think it does based on some other posting in that thread.  Certainly in my
> case it was only altering that which caused/fixed problems.  I think the
> full featured cards make use of the other registers, but because the
> output
> is buffered by the AV7110 (is that right?) the timing is far less
> important

I have taken a closer look into budget-core.c, it seems that only DMA 3 is
used for budget cards.

>
> So - Should I submit a patch?  What would the preferred default be?
>
> Ed W



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