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

Roger James roger at beardandsandals.co.uk
Wed Jan 2 21:29:56 CET 2008


>On Jan 2, 2008 12:14 PM, Roger James <roger <at> beardandsandals.co.uk> wrote:
>> I 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 2.5.19.2 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.
>
>Nope.
>
>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.
>
>Regards,
>
>Mike

Mike

Sorry about the intial post to the wrong list.

Tnanks for the heads up.

The doumentation I have read does not make the fact that you have to leave 
tzap running clear. It does seem a bit counterintuitive for an app that is 
named afer a zapper/remote, you don't expect to keep having to point your 
zapper at the TV to keep the channel tuned :-).

Can anyone point me at somewhere were this is documented/explained. Is there 
some active element in the frontend tuning process that is disabled once tzap 
exits and closes its interfaces to the dvb driver? 

Thanks,

Roger





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