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• Hacking the Popcorn Hour C-200

  3 mai 2010, par Mans — Hardware, MIPS

  Update : A new firmware version has been released since the publication of this article. I do not know if the procedure described below will work with the new version.

  The Popcorn Hour C-200 is a Linux-based media player with impressive specifications. At its heart is a Sigma Designs SMP8643 system on chip with a 667MHz MIPS 74Kf as main CPU, several co-processors, and 512MB of DRAM attached. Gigabit Ethernet, SATA, and USB provide connectivity with the world around it. With a modest $299 on the price tag, the temptation to repurpose the unit as a low-power server or cheap development board is hard to resist. This article shows how such a conversion can be achieved.
  

  Kernel

  The PCH runs a patched Linux 2.6.22.19 kernel. A source tarball is available from the manufacturer. This contains the sources with Sigma support patches, Con Kolivas’ patch set (scheduler tweaks), and assorted unrelated changes. Properly split patches are unfortunately not available. I have created a reduced patch against vanilla 2.6.22.19 with only Sigma-specific changes, available here.

  The installed kernel has a number of features disabled, notably PTY support and oprofile. We will use kexec to load a more friendly one.

  As might be expected, the PCH kernel does not have kexec support enabled. It does however, by virtue of using closed-source components, support module loading. This lets us turn kexec into a module and load it. A patch for this is available here. To build the module, apply the patch to the PCH sources and build using this configuration. This will produce two modules, kexec.ko and mips_kexec.ko. No other products of this build will be needed.

  The replacement kernel can be built from the PCH sources or, if one prefers, from vanilla 2.6.22.19 with the Sigma-only patch. For the latter case, this config provides a minimal starting point suitable for NFS-root.

  When configuring the kernel, make sure CONFIG_TANGOX_IGNORE_CMDLINE is enabled. Otherwise the command line will be overridden by a useless one stored in flash. A good command line can be set with CONFIG_CMDLINE (under “Kernel hacking” in menuconfig) or passed from kexec.

  Taking control

  In order to load our kexec module, we must first gain root privileges on the PCH, and here a few features of the system are working to our advantage :

  1. The PCH allows mounting any NFS export to access media files stored there.
  2. There is an HTTP server running. As root.
  3. This HTTP server can be readily instructed to fetch files from an NFS mount.
  4. Files with a name ending in .cgi are executed. As root.

  All we need do to profit from this is place the kexec modules, the kexec userspace tools, and a simple script on an NFS export. Once this is done, and the mount point configured on the PCH, a simple HTTP request will send the old kernel screaming to /dev/null, our shiny new kernel taking its place.

  The rootfs

  A kernel is mostly useless without a root filesystem containing tools and applications. A number of tools for cross-compiling a full system exist, each with its strengths and weaknesses. The only thing to look out for is the version of kernel headers used (usually a linux-headers package). As we will be running an old kernel, chances are the default version is too recent. Other than this, everything should be by the book.

  Assembling the parts

  Having gathered all the pieces, it is now time to assemble the hack. The following steps are suitable for an NFS-root system. Adaptation to a disk-based system is left as an exercise.

  1. Build a rootfs for MIPS 74Kf little endian. Make sure kernel headers used are no more recent than 2.6.22.x. Include a recent version of the kexec userspace tools.
  2. Fetch and unpack the PCH kernel sources.
  3. Apply the modular kexec patch.
  4. Using this config, build the modules and install them as usual to the rootfs. The version string must be 2.6.22.19-19-4.
  5. From either the same kernel sources or plain 2.6.22.19 with Sigma patches, build a vmlinux and (optionally) modules using this config. Modify the compiled-in command line to point to the correct rootfs. Set the version string to something other than in the previous step.
  6. Copy vmlinux to any directory in the rootfs.
  7. Copy kexec.sh and kexec.cgi to the same directory as vmlinux.
  8. Export the rootfs over NFS with full read/write permissions for the PCH.
  9. Power on the PCH, and update to latest firmware.
  10. Configure an NFS mount of the rootfs.
  11. Navigate to the rootfs in the PCH UI. A directory listing of bin, dev, etc. should be displayed.
  12. On the host system, run the kexec.sh script with the target hostname or IP address as argument.
  13. If all goes well, the new kernel will boot and mount the rootfs.

  Serial console

  A serial console is indispensable for solving boot problems. The PCH board has two UART connectors. We will use the one labeled UART0. The pinout is as follows (not standard PC pinout).

          +-----------+
         2| * * * * * |10
         1| * * * * * |9
          -----------+
            J7 UART0
      /---------------------/ board edge
  

  Pin	Function
  1	+5V
  5	Rx
  6	Tx
  10	GND

  The signals are 3.3V so a converter, e.g. MAX202, is required for connecting this to a PC serial port. The default port settings are 115200 bps 8n1.

• Revision 4b017d0bbada5062ecfc2ae9a4402c835b9cc9d3 : [15674] avait oublié de traiter le cas où on ne passe pas le lien en ...

  22 août 2010, par b_b — Log

  >doc1] ...">[15674] avait oublié de traiter le cas où on ne passe pas le lien en paramètre aux modèles (réparer les boutons de download sur spip.net) git-svn-id : svn ://trac.rezo.net/spip/branches/spip-2.1@15968 caf5f3e8-d4fe-0310-bb3e-c32d5e47d55d

• Easy Tricks for Finding WebM Videos in YouTube

  9 août 2010, par noreply@blogger.com (John Luther)

  Since the WebM project launch, YouTube has been encoding videos uploaded at 720p or higher resolution in the WebM format. Today, the one million most popular videos of any size on YouTube are also available in the WebM format.

  We have instructions on our project site for finding these videos but they require adding a special parameter onto the end of each search query. All of the browsers that support WebM can create search shortcuts with custom parameters, however, so we’ve compiled instructions for making it very simple to search for WebM videos in YouTube.

  Important : First, make sure you have a supported browser and are enrolled in the YouTube HTML5 beta by going to http://youtube.com/html5 and clicking Enter the HTML5 Beta.

  Creating a WebM Search Shortcut

  Firefox 4 Beta :
  

  1. Select Bookmarks > Organize Bookmarks. A bookmark manager dialog opens.
  2. In the left column, choose a location for the new bookmark you’re creating. Next, choose Organize > New Bookmark (on MacOS click the gear icon). The new bookmark dialog opens.
  3. In the Name box, type WebM.
  4. In the Location box, type http://youtube.com/results?search_query=%s&webm=1.
  5. In the Keyword box, type webm.
  6. Click Add.

  Google Chrome Early Release Channel :
  

  1. On Windows and Linux, click the Chrome wrench icon in the toolbar and select Options. On MacOS, select Chrome > Preferences.
  2. On the Basics tab, click the Manage button in the Default Search section.
  3. On Windows and Linux, click Add. On MacOS X, click the plus (+) button.
  4. In the Name box, type WebM.
  5. In the Keyword box, type webm.
  6. In the URL box, type http://youtube.com/results?search_query=%s&webm=1.
  7. Click OK.

  Opera 10.60 and later :
  

  1. Go to http://youtube.com.
  2. Right-click in the YouTube search box at the top of the page and select Create Search. On MacOS, use Ctrl+click if you don’t a secondary mouse button enabled.
  3. In the Name box, type WebM.
  4. In the Keyword box, type webm.
  5. In the Address box, type http://youtube.com/results?search_query=%s&webm=1.
  6. Click OK.

  
  

  
  Now you’re ready to search. In the location box of the browser, type webm monster trucks. The YouTube search results page will open with a selection of monster truck videos encoded in the WebM format. When watching a video, look for the HTML5 WebM indicator in the player control bar.

  If you can’t find WebM videos it is most likely a browser cookie problem. Your enrollment in the YouTube HTML5 beta test is stored in a browser cookie (not in your YouTube or Google account), and that cookie can expire. Visit http://youtube.com/html5 and opt-in again to re-set the cookie.

  Directly Accessing WebM Videos by URL

  To find out if any YouTube video is available in WebM, simply add &html5=True (make sure True is capitalized) to the end of the video URL. If there is a WebM version of the video, it will open instead of the Flash version. For example :
  

  • Flash version : http://www.youtube.com/watch?v=Dz6gFokvOr0
  • WebM version : http://www.youtube.com/watch?v=Dz6gFokvOr0&html5=True