[linux-dvb] Re: Network: a new hope

["Robert Schlabbach" <robert_s@gmx.net>]

From: <emard@softhome.net>
> As you well know by now, dvb_net is seduced by the dark side,
> resulting in packet loss.
>
> I was investigating the packet loss on a budget class card, latest
> CVS from weekend and 2.4 and so far I came to this conclusion:

Sorry, I haven't followed this issue right from the start: Does it occur
_only_ on budget class cards with the SAA7146A on it? Because I recently
investigated budget DMA issues with the SAA7146A and found that it tends to
not properly fulfill DMA requests - depending on configuration, it can
randomly not transfer Dwords within the data stream (but will advance the
pointer).

The resulting stream can actually look perfectly ok according to the MPEG-2
headers (no continuity count errors), but the actual packet contents will
be corrupted.

If this is indeed an SAA7146A/budet issue and you're willing to invest some
time into this, you should start by modifying the budget DMA code so that
it pre-initializes each buffer before it is DMA'd to with a certain DWORD
pattern, and after the DMA checks whether the pattern is still found
anywhere in the buffer (of course, any pattern can always appear in the
real data, but a wisely chosen pattern would only show up once in a blue
moon, and you can tell by the frequency whether it is real data or DMA
corruption)...

Regards,
--
Robert Schlabbach
e-mail: robert_s@gmx.net
Berlin, Germany



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