Em28xx PAL VBI

With the HVR-1600 ALSA stuff completed and being validated, I switched over to wrapping up the outstanding em28xx VBI support for PAL. Since I do not have access to a teletext signal here in the United States, I have taken a two-phase approach to adding the support.

Phase 1 involves local validation using a well-defined PAL signal source that contains VBI. Fortunately, Andy Walls was very helpful in mailing me a CD a couple of months ago with some MPEG samples that include such info, and that can be used in conjunction with an old Hauppauge PVR-350 that has “TV out” functionality:

[lightbox title=”Em28xx PAL VBI” href=”../../blog/wp-content/uploads/2009/11/CIMG0131.jpg”][/lightbox]

(Click on the image above for full version)

As you can see, I had to hack around the lack of an output cable for the PVR-350. Crude, but effective.

So, for phase 1, we added the necessary code and debugged it with a capture that contains Widescreen Signalling (WSS) VBI information. As you can see below, it’s working!

[lightbox title=”Em28xx PAL VBI” href=”../../blog/wp-content/uploads/2009/11/pal_vbi.png”][/lightbox]

(Click on the image above for full version)

I included the above screen capture because it shows not only the tvtime output, but the various tools that are useful in debugging VBI issues. In particular, the “./capture” test tool that comes with zvbi, as well as the “osc” tool which allows you to view the actual VBI waveform. This approach was *considerably* easier/faster than when I did it for NTSC, where I had used a combination of a version of the zvbi-ntsc-cc that I added a bunch of debug to, as well as using OpenOffice to plot the waveform.

Now that I’m at the point where the PAL VBI support is working in general (and not crashing my development platform), we’ll move on to phase 2, which is to debug on a remote platform provided by the customer, which has access to a live Teletext stream.

4 thoughts on “Em28xx PAL VBI

  1. Credit where credit is due:
    Hans Verkuil originally provided me with the DVD of PAL MPEG files and also loaner PVR-350 (but with cables)!

    The TV test patterns are courtesy of a TV pattern generator donated by Jeff Campbell to Hans for ivtv work. See the front page credits of

    http://www.ivtvdriver.org

    for Jeff’s company affiliation at the time.

  2. This is great news. Thanks for working on this Devin.

    And I’m glad the generator has come in handy. I was wondering if it was still getting regular use. 🙂

    -Jeff

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