BeagleBox: finding Mr. DSS2


Trying to come to grips with the myriad of source trees from which beagleboard related source can be pulled, I updated the BeagleBoard build system the other day to make it easier to pull from the various archives.  Technically there are four ways to get source related to BeagleBoard:

  • A compressed tarball from a main archive
  • git clone from a repository at the main site
  • GIT clone from a gitorious.org repository
  • GIT clone from someone else

Currently pulling from GIT archives and HTTP sites are supported but extending this to other protocols wouldn't be particularly hard.  Fortunately, most of this code is being managed with GIT.

The main archives are either kernel.org (for the kernel) or denx.de (for the bootloader, u-boot).  Both sites also have GIT repositories.  The gitorious.org site appears to have BeagleBoard developer branches that eventually get pushed to the main archive GIT repositories, which have their own repos and branches that merge their way into the mainlines.  Then there are developer-specific GIT repositories that have special versions of code that hasn't been pushed upstream to gitorious.org and/or the mainlines.  The latter I have yet to deal with but I know they can exist.

The beaglebox build now allows selection of which repository to pull from based on make instead of bitbake.

After putting all this together I can build a variety of combinations of u-boot and kernel.  My goal at this point is to get a working S-video display from my BeagleBoard.  So far, only the validation image builds of u-boot and the kernel have generated any TV output.  However, those builds appear to use DSS1, the original display support for omap processors.  dss2 is the rewritten version and the one I'd like to be using.  Unfortunately, no combination of u-boot and kernel, as of yet, has found any display devices for use with DSS2.  Not even dvi.  I have a TV connected to the s-video port and the TV is turned on prior to booting the board.  The hdmi port is not connected to anything.  Assuming autoprobing I would expect to see the TV display configured but not the DVI.  Still, I have no displays at all.

At this point I'm nearing the end of my trial-and-error approach to finding DSS2 support for tv-out (re: S-Video).  My next test is with u-boot's 2010.09 (mainline GIT) and a kernel from gitorious.org that is from the DSS2 developer (linux-omap-dss2), which is based on linux 2.6.37.  If this test doesn't work, then I'm going to disable the bootloader config check (CONFIG_FB_OMAP_BOOTLOADER_INIT) in the kernel and try again.  That should force the kernel to enable DSS2 displays without any help from the bootloader.

If that doesn't work, it's time to start pinging developers.  I'm just not sure who to ping first.  Posts about this to the BeagleBoard mailing list have not generated much response and my assumption based on posts to the list is that everyone is doing either HDMI or dvi-d (via HDMI) or has a VGA daughterboard on their BeagleBoards.  Not much TV-out discussion there that I've seen recently.  The other option is the linux-omap mailing list mentioned by the maintainer of the linux-omap-dss2 repo (Tomi's kernel tree is the link from elinux.org.) on gitorious.org.  However, he doesn't say where you can go to get on or access that list.  So I'll have to google around to find it (maybe elinux.org has a link).

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