[linux-dvb] Transport errors on Twinhan DST tuners (both DVB-S and DVB-T)

["Werner Johansson" <wj@yodel.net>]

Hi,

After doing some testing here, I have seen very few transport errors (the
error bit in the TS header set) on my DVB-S cards, with marginal signal I
get a few packets bad once every _hour_ or so, so that's perfectly
acceptable, but on my DVB-T card it always occurs in bursts with at least
16, sometimes up to 192 packets in a second, and this repeats itself once
every few seconds up to once every 30 seconds if I'm lucky.

I have much better signal-to-noise ratio reported from the DVB-T card, but
that's probably just a frontend/tuner difference between the S and T cards. 

I have checked whether INVERSION_AUTO or ON/OFF would make any difference,
but unfortunately no. The Guard interval and code rate is correct, even
tried FEC_AUTO with exactly the same results.

I have ruled out PCI DMA/IRQ problems as I get the correct transport stream
without "broken" half TS packets, it's just that the error bit gets set a
lot by the T-card. and the packets are indeed corrupted. No errors gets
logged anywhere which would point to a driver problem, this seems to be
entirely caused by the frontend.

The transport error bit has been up for discussion here before, but that was
for a different frontend. Now I'm curious how the Twinhan frontend handles
this - can I depend on that the packet is completely OK if the error bit is
clear, or can there still be errors in there? Can this behaviour differ
between the different frontends?

I have no problems getting the frontend to lock on to the channels, and the
DST tuner interface seems to handle the frequency conversion internally in
the ASIC, so it shouldn't be a frequency issue, right? Anyway I tried both
increasing and decreasing the tuned frequency, and increasing it 100-200kHz
seems to lower the error rate somewhat, although not completely eliminated.
Can there be some offset error in the ASIC, or other hardware problems?

/Werner