So at least six months ago now, I was first contacted by Scott Davilla of XBMC and AppleTV fame, whom I’ve had misc conversations with a number of times previously, (mostly about running MythTV on the AppleTV under Linux), about a very cool new toy he was playing with that would allow the AppleTV to play back 1080p h.264 material nice-n-smooth. Well, really not all that new a device, just new in the sense that there was actual traction on an open-source driver for it seeing the light of day. That device was the Broadcom Crystal HD decoder card, aka the BCM970012.
Now, the Crystal HD has been available as an OEM add-on for a number of systems with Windows drivers for a few years now, and prior to that, I think earlier incarnations existed in various set top boxes (which possibly were running some form of embedded Linux…). Dell has been shipping the decoder card for a while as the “Broadcom BD Accelerator card”. That would be BD and in “Blu-Ray Disc”. However, don’t get too excited about the prospect of a Linux Blu-Ray Disc playback solution just yet. More on that later… HP has been bundling the same card with their Mini 110 systems. Not too long ago, one of my favorite smaller online shops (juxtaposed to newegg or amazon), Logic Supply, which carries lots of hard-to-find-anywhere-else mini-itx and assorted embedded stuff, started selling the card as well.
Anyhow, Scott had put out some feelers about the Crystal HD, and managed to make contact with someone in Broadcom’s MediaPC division, who was in fact looking for community folks to help with Linux driver support. Amusingly, not long after I’d first talked to Scott about this, I talked to a guy I play pickup soccer with, who also happens to work for Broadcom, and he said he’d dig around and see if he could get me the name of someone to talk to about the Crystal HD as well. The name he turned up was the very same individual Scott had been talking to. Now, as you may or may not know, I happen to work for Red Hat, in its kernel group. I’m far from an elite kernel hacker myself, I’m just a trainee, if you ask me, but I work with some absolutely brilliant kernel people. This is attractive to someone like Broadcom looking for help with their kernel driver. Needless to say, the ball started rolling rather quickly at that point, and Broadcom’s Naren Sankar gave the thumbs up for Scott to pass along a copy of the full kernel driver and userspace library source for me to start poking at.
The code was… Well, typical of a lot of vendor code. For the most part, I cared first and foremost about the kernel driver. Lots of wrapper functions, rather than using kernel functions directly, Windows ifdeffery, and so on. But generally, pretty well laid out and thorough code, with reasonably good documentation in headers about what functions did, what register contents meant, etc. Okay, so on to compiling… Or not. My main development systems are pretty much all 64-bit Fedora, with fairly up-to-date kernels. Double-fail on that one. I can’t remember the exact details anymore, but it pretty much only worked on an older 32-bit kernel — Red Hat Enterprise Linux 5′s 2.6.18 kernel worked, as did Ubuntu 8.04′s kernel. If you’re gonna get the thing upstream, its kinda gotta work on the latest kernel, and be portable to 64-bit. So that was the focus of my late-night efforts for the next few weeks. Getting it to build on newer kernels wasn’t too much work. Making it build on 64-bit kernels was a lot more work. Then getting it to actually *work* on a modern 64-bit kernel was even more work. But now it does.
There was a bunch of additional code reformatting involved as well, so the driver looked more like Linux kernel code, then some assorted sanitization (libcrystalhd was originally called libldil — ldil being ‘linux driver interface library’ or something like that, and the crystalhd kernel module was originally called mpclink, iirc), new license headers, etc., a few more rewrites here and there to satisfy Broadcom legal, and finally, on December 29, 2009, a public release of the Linux kernel driver under the GPL, the Linux userspace library under the LGPL. From there, a bit more clean-up (being tracked in a git tree, of course), a submission of the driver to the Linux Kernel Mailing List by someone other than those of us who’d been working on it for the past 6 months (Manu Abraham graciously stepped aside when he found out we’d been working on it and planned to submit it), and then we finally got something off to lkml. On January 6, 2010, the driver was merged into the Linux kernel staging tree. Woo!
I’ve also patched the driver into the latest Fedora 12 and rawhide (F13-to-be) kernel trees, and submitted the userspace library as a new package for Fedora. Note that the firmware doesn’t yet have a license upon it that permits redistribution (redistributable, no modification, a la many other kernel driver firmware files), but Naren was working with Broadcom legal to make that happen. Note that the git tree I’m hosting builds on kernels going back at least as far as 2.6.18 (2.6.11, I think, but I’ve only tried back to 2.6.18 myself), and there’s source for a gstreamer plugin included in the tree. If you look at the Fedora package review bug, you’ll note that it doesn’t work so hot with current gstreamer, but it does work on older versions, and I’m hoping to get some help from one of Red Hat’s gstreamer gurus to fix it up to work with more current bits…
Speaking of firmware and getting back to that Blu-Ray Disc playback issue… The firmware for Linux does NOT include support for Blu-Ray Disc decoding. There are all sorts of “trusted path” requirements that would be… trick… to meet with an open-source driver. The driver doesn’t have code to support BD even if you did try loading firmware from a Windows driver that purported to support BD playback. Oh well.
Now, what we *can* support, is playback of MPEG2, h.264 and VC1 files. Without violating any (admittedly STUPID) codec patents here in the US or having to purchase a license. The decoding is all done in hardware. With almost no cpu usage. (Almost, because we do have to dma the encoded bitstream into the decoder, then dma out very large buffers full of raw video frames, and transplant that over to your gpu, but an AppleTV with its 1GHz proc can handle 1080p h.264 with this thing, so can a single-core Atom N270).
Scott has been hard at work adding Crystal HD support to XBMC and a port of the driver and library to Mac OS X, and has made excellent progress. Edward ‘gimli’ Hucek has been working on a xine plugin. Word has it a few ffmpeg developers have starting poking at support there too — which is the part I’m personally most interested in, as MythTV can inherit that work. (I actually started poking at MythTV code myself, seeing what needed to be added where to support the Crystal HD, but I’ve not had time to get up to speed on the code, nor will I likely anytime soon, and quite frankly, its probably better if the ffmpeg guys do the work, I’m really nowhere near as comfortable working outside the kernel… .
Oh, there’s also a very crude smoke-test app in examples/ in the crystalhd source tree. Its hard-coded to a specific video type in a specific file path, but its useful for sanity-checking if the decoder is working. It doesn’t display anything, it just takes in a clip, decodes frames, and spits back a bit of data about them, discarding the actual decoded video frame. More of just a developer usage thing, good for headless setups where ssh’d into a machine and the like. Ping me and/or Scott if you want to poke at it and need help making it behave, but most of the gory details can be seen in the post and comments over here in the Breaking Eggs And Making Omelettes blog, which if I understand correctly, belongs to one of the ffmpeg developers…
So yeah, that’s about where things are at right now… Stay tuned for updates, I’ll try to keep on top of them here…