[linux-dvb] Tuner drifts out of lock after tzap is exited

Michael Krufky mkrufky at linuxtv.org
Wed Jan 2 18:26:38 CET 2008

On Jan 2, 2008 12:14 PM, Roger James <roger at beardandsandals.co.uk> wrote:
> If have been struggling for a couple of days trying to get decent NIT dumps
> off a local multiplex. Using tzap to tune a channel, exiting tzap and then
> running dvbsnoop, it seemed very variable whether I found the table before
> timing out. I noticed I had more success I kept retuning the frontend using
> tzap before each dvbsnoop run. But even then it would quite often produce
> nothing. I knew the driver and rf side setup was good because mtyhtv was using
> all the devices and multiplexes successfully. On checking the kernel logs I
> found I was getting a lot of cx8802_timeout messages on unsuccessful runs. So
> I tried a test running tzap, waiting till the frontend had lock, then exiting
> tzap and running femon. As I suspected, after a few seconds femon reported
> that the frontend had lost lock. So I a tried the dvbsnoop test with tzap left
> running in another session. Result, everything worked perfectly.

Exactly as expected.

> I am running debian stable with a kernel.
> Is this expected behaviour? Can anyone explain to me what is happening?

Yes.  The moment tzap is stopped, tuning ceases.  Also, if you don't
specify -r to tzap, you'll get nothing from the dvr device.

> In the past I had always assumed that could exit tzap after you had tuned a
> channel and the fe would stay locked as long as signal remained good.


Always keep tzap running when performing this type of testing.

Also, you sent this email to the video4linux mailing list, which only
deals with analog video.  cc added to linux-dvb, which is more
appropriate for this topic.

I hope this helps.



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