[mythtv-commits] Re: Ticket #264: PMT always on fails CRC check

MythTV mythtv at cvs.mythtv.org
Mon Aug 29 13:42:21 UTC 2005

#264: PMT always on fails CRC check
 Reporter:  danielk  |        Owner:  danielk
     Type:  defect   |       Status:  closed 
 Priority:  minor    |    Milestone:         
Component:  mythtv   |      Version:  head   
 Severity:  medium   |   Resolution:  fixed  
       Cc:           |  
Changes (by danielk):

  * resolution:  => fixed
  * status:  assigned => closed


 (In [7169]) Fixes #264.

 The "VLSI VES1x93 DVB-S" and "Philips TDA10046H DVB-T" DVB
 cards occasionaly munge the PMT. The PMT is still readable
 but the CRC check fails. This commit changes MythTV so that
 it does not do a CRC check on the PMT for these cards

 I'm assuming these cards read the PMT and write it out again
 much as MythTV does (probably to support CA since this only
 happens on the PMT). But unfortunately they change something
 (presumably the padding) without recalculating the CRC.
 If this assumption is correct these cards presumably verify
 the original CRC before rewriting the PMT, so it is safe
 to not check the CRC.

 If I'm incorrect and these cards don't check the CRC then this
 is still relatively safe since these packets had to get past
 the error correction layer and the odds that the relatively
 infrequent and small PMT's have enough bit flips to get past
 EC with errors is very low.

Ticket URL: <http://cvs.mythtv.org/trac/ticket/264>
MythTV <http://www.mythtv.org/>

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