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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.

• Announcing the first free software Blu-ray encoder

  25 avril 2010, par Dark Shikari — blu-ray, x264

  For many years it has been possible to make your own DVDs with free software tools. Over the course of the past decade, DVD creation evolved from the exclusive domain of the media publishing companies to something basically anyone could do on their home computer.

  But Blu-ray has yet to get that treatment. Despite the “format war” between Blu-ray and HD DVD ending over two years ago, free software has lagged behind. “Professional” tools for Blu-ray video encoding can cost as much as $100,000 and are often utter garbage. Here are two actual screenshots from real Blu-rays : I wish I was making this up.

  But today, things change. Today we take the first step towards a free software Blu-ray creation toolkit.

  Thanks to tireless work by Kieran Kunyha, Alex Giladi, Lamont Alston, and the Doom9 crowd, x264 can now produce Blu-ray-compliant video. Extra special thanks to The Criterion Collection for sponsoring the final compliance test to confirm x264′s Blu-ray compliance.

  With x264′s powerful compression, as demonstrated by the incredibly popular BD-Rebuilder Blu-ray backup software, it’s quite possible to author Blu-ray disks on DVD9s (dual-layer DVDs) or even DVD5s (single-layer DVDs) with a reasonable level of quality. With a free software encoder and less need for an expensive Blu-ray burner, we are one step closer to putting HD optical media creation in the hands of the everyday user.

  To celebrate this achievement, we are making available for download a demo Blu-ray encoded with x264, containing entirely free content !

  On this Blu-ray are the Open Movie Project films Big Buck Bunny and Elephant’s Dream, available under a Creative Commons license. Additionally, Microsoft has graciously provided about 6 minutes of lossless HD video and audio (from part of a documentary project) under a very liberal license. This footage rounds out the Blu-ray by adding some difficult live-action content in addition to the relatively compressible CGI footage from the Open Movie Project. Finally, we used this sound sample, available under a Creative Commons license.

  You may notice that the Blu-ray image is only just over 2GB. This is intentional ; we have encoded all the content on the disk at appropriate bitrates to be playable from an ordinary 4.7GB DVD. This should make it far easier to burn a copy of the Blu-ray, since Blu-ray burners and writable media are still relatively rare. Most Blu-ray players will treat a DVD containing Blu-ray data as a normal Blu-ray disc. A few, such as the Playstation 3, will not, but you can still play it as a data disc.

  Finally, note that (in accordance with the Blu-ray spec) the disc image file uses the UDF 2.5 filesystem, which may be incompatible with some older virtual drive and DVD burning applications. You’ll also need to play it on an actual Blu-ray player if you want to get the menus and such working correctly. If you’re looking to play it on a PC, a free trial of Arcsoft TMT is available here.

  What are you waiting for ? Grab a copy today !

  UPDATE : Here is an AVCHD-compliant version of the above, which should work better when burned on a DVD-5 instead of a BD-R. (mirror)
  

  What’s left before we have a fully free software Blu-ray creation toolkit ? Audio is already dealt with ; AC3 audio (aka Dolby Digital), the format used in DVD, is still supported by Blu-ray, and there are many free software AC3 encoders. The primary missing application is a free software Blu-ray authoring tool, to combine the video and audio streams to create a Blu-ray file structure with the menus, chapters, and so forth that we have all come to expect. But the hardest part is dealt with : we can now create compatible video and audio streams.

  In the meantime, x264 can be used to create streams to be authored using Blu-Print, Scenarist, Encore or other commercial authoring tools.

  More detailed documentation on the new Blu-ray support and how to use it can be found in the official commit message. Do keep in mind that you have to export to raw H.264 (not MKV or MP4) or else the buffering information will be slightly incorrect. Finally, also note that the encoding settings given as an example are not a good choice for general-purpose encoding : they are intentionally crippled by Blu-ray restrictions, which will significantly reduce compression for ordinary non-Blu-ray encoding.

  In addition to Blu-ray support, the aforementioned commit comes with a lot of fun extras :

  x264 now has native variable-framerate ratecontrol, which makes sure your encodes get a correct target bitrate and proper limiting of maximum bitrate even if the duration of every frame is different and the “framerate” is completely unknown. This helps a lot when encoding from variable-framerate container formats such as FLV and WMV, along with variable-framerate content such as anime.

  x264 now supports pulldown (telecine) in much the same fashion as it is handled in MPEG-2. The calling application can pass in flags representing how to display a frame, allowing easy transcoding from MPEG-2 sources with pulldown, such as broadcast television. The x264 commandline app contains some examples of these (such as the common 3:2 pulldown pattern).

  x264 now also exports HRD timing information, which is critical for compliant transport stream muxing. There is currently an active project to write a fully DVB-compatible free software TS muxer that will be able to interface with x264 for a seamless free software broadcast system. It will likely also be possible to repurpose this muxer as part of a free software Blu-ray authoring package.

  All of this is now available in the latest x264.

  http://mirror05.x264.nl/Dark/bluray%20fail.png

• Opera 10.60 Released with WebM Support

  7 juillet 2010, par noreply@blogger.com (John Luther)

  Congratulations to everyone at Opera Software for releasing version 10.60 of their browser, which supports WebM video playback. Downloads for Windows, Mac OS and Linux are available on the Opera download page.