[linux-dvb] Re: Newbie questions

[Bruno Prior <bruno@rpgd.uklinux.net>]

Gavin Hamill wrote:
>
> 2) Try the card in Windows! Make sure you don't actually have a duff
> one! :)

Right. I've tried sticking the Nova-T in Rachel's computer, which is
dual-bootable Win98 and Mandrake 9.0. Windows recognized the new
hardware and the drivers installed OK. The software installed OK too.
The first attempt to run the software, where the configuration dialog
tries to scan for channels, crashed Windows. After reboot, the second
run of the software went OK. It found the expected services on the local
frequencies. It tuned to and showed the various BBC and ITV channels OK,
although with quite a lot of dropped frames (Rachel's TV is on a long
extension off a long extension, which probably explains the poor
quality). It also provided "now and next" data below the viewing window.
So the card works adequately in Windows.

Then I tried rebooting into linux. The first attempt to "make; make
insmod" DVB failed, presumably because Rachel's machine is running
standard Mandrake 9.0 kernel and modules, which included the mod_dvb
modules. So I deleted the mod_dvb modules from the kernel source and
rebuilt the kernel and modules. Rebooted with the new kernel, and "make;
make insmod" of DVB worked this time. I also rebuilt dvbtune to be sure.
./dvbtune -f 505833 -qam 64 -cr 3_4 worked OK. ./dvbtune -f 505833 -qam
64 -cr 3_4 -m worked OK (low Verror rate). ./dvbtune -f 505833 -qam 64
-cr 3_4 -i crashed linux hard.

So I rebooted and after a long fsck (the crash seemed to have caused a
lot of corruption) got the DVB modules inserted again. This time,
./dvbtune -f 505833 -qam 64 -cr 3_4 -i did not crash the machine, and
actually reported some services. However, it was various EMAP, MTV and
UKTV services, rather than the BBC services I was expecting. So I tried
again on 481833kHz, but this simply gave a "Nothing to read from fd_sdt"
error. So I went back to 505833kHz and this time, that gave me a
"Nothing to read from fd_sdt" error too".

To cut a long story short, I tried the various frequencies that should
work in this area many times, and the results were consistently
inconsistent. The best example was a series of four attempts to tune to
561833kHz. The four successive attempts found the following services:

1. BBC PARLMNT / BBC 4 / CBeebies / various BBC radio channels
2. Sky News / Sky Spts News / Sky Travel / UKHistory
3. ITV 1 / ITV 2 / Channel 4 / ITV News / Teletext
4. Nothing to read from fd_sdt

Each attempt reported something pretty close to the following at the
start (only difference would be small changes in Bit error rate and SNR):

Using DVB card "Grundig 29504-401"
tuning DVB-T (in United Kingdom) to 561833000 Hz
polling....
Getting frontend event
FE_STATUS: FE_HAS_SIGNAL FE_HAS_LOCK FE_HAS_CARRIER FE_HAS_VITERBI
FE_HAS_SYNC
Event:  Frequency: 561833000
         SymbolRate: 0
         FEC_inner:  2
Bit error rate: 414
Signal strength: 12079
SNR: 54741
FE_STATUS: FE_HAS_SIGNAL FE_HAS_LOCK FE_HAS_CARRIER FE_HAS_VITERBI
FE_HAS_SYNC
<transponder type="T" freq="561833000">

So dvbtune claimed to be tuning to 561833 each time, but was finding
different services every time. As far as I understand it, that is
impossible. The only conclusion is that dvbtune is actually tuning
randomly to one of the channels when it is claiming to be tuning to the
channel you instructed it to.

Given that it worked in Windows, it doesn't look like hardware is
causing the problem. I had fully expected the problem to be down to some
act or omission of mine. But I am now increasingly convinced there is
something pretty badly wrong with dvbtune.

Having said that, I think there may be a hardware problem as well. I
have just reinstalled the Nova-T in my machine and when I have run
dvbtune with -i, the machine crashed. This is exactly what happened on
Rachel's machine, and is probably pretty similar to when Windows crashed
when first scanning for Channel info. This seems fairly consistent
across the different platforms. No idea what might cause it, or why
running the same command after rebooting after the crash does not cause
another crash.

And there is definitely some difference between Rachel's machine and 
mine. dvbtune on my machine gives me consistent "Nothing to read from 
fd_pat; Nothing to read from fd_sdt" errors, whereas on Rachel's I get 
all sorts of responses, but never anything about fd_pat, only fd_sdt. I 
am wondering if the connection between the two problems is that dvbtune 
never tunes the card correctly on either machine, but on my machine it 
is stuck on one constant channel, whereas on Rachel's it flits between 
channels.

What do you think?

> It's a bizarre install - Windows installs it as a Network device - and
> when I tried it, I ended up having to set a static IP address for the
> Nova card... Very shoddy.

Agreed. I had to do the same. Probably wouldn't have figured that out
for a while if you hadn't have warned me.

Cheers,

Bruno




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