[linux-dvb] Re: DVB-S into Budget modification

[Roberto Deza <rdeza@unav.es>]

Hi Emard,

At 11:43 29/12/2002 +0100, Emard wrote:

[frequency of crashes]
>... Also check with lspci/setpci that the pci latency is 128 for 
>7146 dvb cards and that pci is runing at 33MHz, (no 66Mhz pci or some
>overclocking). It didn't reduce crash frequency for me but this is the
>right way and will improve pci throughput of dvb cards.
>
>Finally I found out that shuffling dvb and/or other cards from one pci slot
>to another, affects the crash frequecy. If I move pci cards differently
>I can also reproduce few minutes crash.

On the PC that I'm doing the tests (Dell Optiplex Gn+; Pentium @200MHz),
there is only two PCI slots, used for the DVB-S card and a NIC (RTL8139C);
I checked early '/proc/interrupts' and 'lspci', without remember to have
any IRQ conflict; there isn't any indication of the PCI
speed, but with the age of this PC and its limited rattings, I would not
hope to find anything better that 33 MHz.

After your comment, I've removed the NIC and set the PCI Latency to 128;
then loaded the (modified) DVB drivers; again, there isn't any shared IRQ;
the surprise is that VDR now works!!! and is possible to interact 
with it; playing old records works fine and while recording, the image/
sound is OK, but the new records don't play well (starting from top of
screen are three areas, the first from the record, the second a big 
"mesh of artifacts" and the third is the old and unmodified picture; seems
as all PES packets are invalid somewhere and its "expasion" abort,
without complet any frame). Thinking on HD performance, I tested it with
'hdparm -tT /dev/hda' and the results was about a 20% lower (HD read at
~10 MB/sec); a few seconds after the test end, I got the "normal" Kernel
Panic (by first time, the crash happened after about 10 minutes!!!).

For the next attempt, I've added the NIC at the same PCI slot (no shared
IRQ's) and forgot to change the PCI Latency; again, VDR works with my 
modified drivers and card (there is the same broken recordings); after 
lots of tests, the crash have lasted 65 minutes. On some way, to have 
used the PC without the NIC have modified the BIOS "Plug & Play" info 
and the behaviour of the system.

Well, without understand anything :-(, now that the system sometimes
works, seems that are more problems to solve.

>I can only speculate, but this crashes IMHO are coming because dvb cards
>sends interrupt or DMA transfer at the time CPU is not expecting it to
>happen, doing other things and so it crashes. Different pci slots in 
>conjunction with nortbridge/southbridge bus priority and cpu speed results 
>sometimes, for some happy people, that by chance CPU manages to execute all 
>critical points and becomes ready to accept dvb when it activates itself.

The subject is so complicated that I wouldn't dare to speculate.

>Therefore, disabling onboard ARM of DVB-S completely and using just your 
>hardware modification one can get cleaner card behaviour free of strange
>firmware and also cleaner driver structure. Then DVB-S would work in Budget 
>only mode and should be much more stable.

But we want also the "transfer mode" and OSD !, to have the good image/
sound that have the premium cards!; that's, have the best of both cards, 
on one :-).


Best regards:
--
Roberto Deza Asensio
Universidad de Navarra
Data Procesing Center
rdeza@unav.es


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