[linux-dvb] Lost lock problems over extended periods of time

Manu Abraham manu at kromtek.com
Tue Jun 7 15:30:47 CEST 2005

Andrew de Quincey wrote:
> Hi, I've been having (another :) problem with the DVB drivers. Basically, at 
> certain sites and with certain channels, cards seem to lose the lock after a 
> while.... the average is about 10 hours, so I think its unlikely to be that 
> multiswitch incompatability with certain TT DVB-S cards. 
> This doesn't affect all sites or all channels or all cards - the same channels 
> at another site can be rock solid with no issues for months.
> The driver is supposed to launch a zigzag scan if it loses lock. However this 
> doesn't ever seem to regain the lock with this problem. Simply restarting our 
> streaming software (without a reboot) however, _does_ regain the lock (only 
> to lose it again after a while).
> Snooping with dvbsnoop shows that the signal has been lost, but it does appear 
> to be zigzagging to try and require it, but failing (I see the lock status 
> varying between SIGNAL and SIGNAL|CARRIER|VITERBI, but never above that).
> The difference between locking initially and losing a lock after a while seems 
> to be the call to dvb_frontend_init(). I'm going to try adding a call to this 
> in to the dvb_frontend_thread() loop if it loses the lock after a while.
> I'm wondering if anyone else sees this? It seems to plague us constantly. 

I had that problem sometime back on the Twinhan cards, that time i 
thought it was because the tuners getting too hot.. As a temporary 
arrangement i tried a huge blower on the cards. This kept the 3 tuners cool.

This never had any effect, whether the tuner was hot/cold.

> There does not appear to be any discernable pattern - we have a wide 
> selection of TT DVB-S card vintages, and it can happen on any one of them, 
> from cards that were bought 2 or 3 years ago to cards that were bought 2 
> months ago. :(

Exactly. That was the time i was looking for continuity errors and so 
on, which Emard had a patch to the lossless section. But even that did 
not have any fix for me.

That made me to think that it was the driver. At that point i was 
digging in the driver. But nothing in the driver was showing up that 
could cause a loss of lock.

The periods used to vary, don't know what exactly caused them to vary 
either. The variations used to happen something like what you said 10 ~ 
12 hours or sometime it was 48 hours. But 72 hours seemed the maximum 
that it would go many times.

Somebody at one of the universities in prague who was streaming in the 
unversity campus also had the same problems....

> Does anyone have any ideas as to why it would be happening? The only thing I 
> can come up with is that the frontends just lose the lock after a bit, so 
> they need to be retuned to work around it.

Yes, reloading the drivers/retuning seemed to solve this problem .. 
Since i have not gone back to that area, don't know whether the problem 
still persists.

I could possibly try this out again after a few days..

> I suppose these cards are really meant as consumer grade ones for zapping 
> channels, and not really designed for 24x7 reception on a single channel. 

I don't think it was the hardware, as the drivers from the manufacturer 
worked fine, eventhough they had their own share of the problems and 
bugs.. :-(


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