[mythtv] simple DEC-2000t fixes for 0.l8

Taylor Jacob rtjacob at earthlink.net
Wed Apr 20 11:27:33 UTC 2005


Quoting Nathaniel Daw <daw at gatsby.ucl.ac.uk>:

> Two very simple code changes are required to get channel scanning and EIT
> working with the DEC-2000t, which is a usb terrestrial dvb box. The
> problem seems to be that this box or its driver (presumably due to USB 1.1
> bandwidth) doesn't send service packets unless you specifically request
> the exact packet type with a filter ioctl -- a permissive mask doesn't
> work. So for instance if I dvbsnoop 0x11 I get nothing, but if I dvbsnoop
> -f 0x42 0x11, I get channel descriptors. And dvbsnoop -f 0x46 -m 0xfb 0x11
> only gives me 0x46 packets (channels on other transmitters), not 0x42
> (channels on the current transmitter).

<big snip>

It's not as trivial as you make it sound.. There are reasons most of the masks
were chosen the way they are.. There are some networks that misuse the 0x46 and
0x42 tables and have them inverted.. EIT also seems to be barely within spec as
i've seen it most of the time and its easier to just read whatever is being
sent on that PID instead of opening up a pile of section filters..

You may want to post on linux-dvb and see if there is some reason for this
hardware acting like this.. I can't believe that the bandwidth on the PIDs with
EIT would make that big of a difference. Then again USB 1.1 isn't a very fat
pipe..

Taylor


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