[linux-dvb] Descrambling suddenly stops

Manu Abraham abraham.manu at gmail.com
Fri Nov 25 09:32:01 CET 2005


Andreas U. Trottmann wrote:

>On Tue, Nov 22, 2005 at 06:03:17PM +0100, Sigmund Augdal Helberg wrote:
>
>  
>
>>>What makes the descrambling stop is when your Session Key/Control Word 
>>>changes. This control word is present in the ECM, and is encrypted and 
>>>the service keys present in the EMM. Now when these keys do change, you 
>>>will not see a difference in the CA_PMT message.
>>>
>>>This change need not always be accompanied by a change in the CA_PMT 
>>>message, as the message itself is not composed of EMM's and ECM's.
>>>
>>>So the solution is to send the message continuously, in a timely manner. 
>>>say for example once in 5 minutes, to the module.
>>>      
>>>
>
>  
>
>>I've tried various approaces to this:
>>1: send a capmt update each time the pmt changes. This is not nearly
>>often enough.
>>2: send a capmt update each time a pmt is received. Same as 1
>>3: send a capmt update every 5 minutes as suggested. This seem to give
>>breaks of up to 5 minutes where the stream is not decrypted
>>4: send a capmt  very often (every 10 second). Even this does not give
>>good results. It seem that when the decryption stops it can take up to
>>20 sec before it start again.
>>
>>Any further suggestions is appreciated.
>>    
>>
>
>I've tried to do this, too - indeed, "sometimes" sending CA_PMT
>does "not work" as well, and it has to wait for the next message.
>
>But, it appears that using the non-CVS drivers (plain Linux
>2.6.14.2) gives significantly better results. Of course it is very
>difficult to "prove" that a problem that "sometimes" happens just
>went away, but I now have watched about 60 "channel-hours" with
>2.6.14.2 drivers without any problems (i.e. without the
>descrambling suddenly stopping), while just loading CVS driver
>modules makes the problem appear within minutes.
>
>  
>

The CVS is in sync with the kernel now, so if you can find out what 
changes is causing problems, that would be helpful to understand as to 
what maybe wrong ..


>Unfortunately, I am not able to pinpoint any specific diff right
>now - I'm not even able to see which module might be the culprit.
>Time permitting, I'll try to narrow the field further, and will
>inform the mailing list of my findings. But for now, indeed I'm
>an extremely happy user.
>
>  
>

Some info would be really helpful. Thanks.

>FWIW, I'm using Technisat SkyStar 1 CI cards (Twinhan clones,
>dvb-bt8xx module), Viacrypt official "red" CAMs, Swiss National
>TV keycards, dvbstream and the latest CVS ca_zap.
>
>  
>

Thanks,
Manu





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