While we knew that Lightning accessories packed in an embedded Texas Instruments chip to handle its adaptive 8-pin interface, a new teardown of the $50 Lightning Digital AV Adapter shows that the complexity in some of these accessories is far more than we’ve imagined.
The teardown, done by the folks at Panic software, reveals that the Adapter contains an ARM SoC and a 256MB RAM running what appears to be a mini version of iOS to power the video out functionality on the iPhone, iPad and iPod touch that come with the new Lightning connector.
The folks at Panic noticed this when they saw that the Lightning adapter wasn’t capable of natively sending 1080p video. Moreover, the stream that was sent contained MPEG artifacts indicative of the AirPlay-like lossy compression, which in turn degraded video quality.
From Panic’s post:
There are a lot of questions. What OS does it boot? @jmreid thinks the adapter copies over a “mini iOS” (!) from the device and boots it in a few seconds every time it’s connected, which would explain the fairly lengthy startup time for video out. Why do this crazy thing at all? All we can figure is that the small number of Lightning pins prevented them from doing raw HDMI period, and the elegance of the adapter trumped the need for traditional video out, so someone had to think seriously out of the box. Or maybe they want get as much functionality out of the iPad as possible to reduce cost and complexity. Another floated theory: efficient HDCP [High-bandwidth Digital Content Protection] enforcement [presumably required by hollywood studios].
Sadly, even though this AV adapter is technologically more superior to its predecessors, it’s more of a downgrade due to its non-native 1080p support, the lossy video streaming and in certain cases even laggy performance.
Have you used the Lightning Digital AV Adapter? What has been your experience?
Update: Over at the Panic blog, an anonymous commenter, possibly with internal knowledge about the AV adapter, explains what’s going on here:
Airplay is not involved in the operation of this adapter.
It is true that the kernel the adapter SoC boots is based off of XNU, but that’s where the similarities between iOS and the adapter firmware end. The firmware environment doesn’t even run launchd. There’s no shell in the image, there’s no utilities (analogous to what we used to call the “BSD Subsystem” in Mac OS X). It boots straight into a daemon designed to accept incoming data from the host device, decode that data stream, and output it through the A/V connectors. There’s a set of kernel modules that handle the low level data transfer and HDMI output, but that’s about it. I wish I could offer more details then this but I’m posting as AC for a damned good reason.
The reason why this adapter exists is because Lightning is simply not capable of streaming a “raw” HDMI signal across the cable. Lightning is a serial bus. There is no clever wire multiplexing involved. Contrary to the opinions presented in this thread, we didn’t do this to screw the customer. We did this to specifically shift the complexity of the “adapter” bit into the adapter itself, leaving the host hardware free of any concerns in regards to what was hanging off the other end of the Lightning cable. If you wanted to produce a Lightning adapter that offered something like a GPIB port (don’t laugh, I know some guys doing exactly this) on the other end, then the only support you need to implement on the iDevice is in software- not hardware. The GPIB adapter contains all the relevant Lightning -> GPIB circuitry.
It’s vastly the same thing with the HDMI adapter. Lightning doesn’t have anything to do with HDMI at all. Again, it’s just a high speed serial interface. Airplay uses a bunch of hardware h264 encoding technology that we’ve already got access to, so what happens here is that we use the same hardware to encode an output stream on the fly and fire it down the Lightning cable straight into the ARM SoC the guys at Panic discovered. Airplay itself (the network protocol) is NOT involved in this process. The encoded data is transferred as packetized data across the Lightning bus, where it is decoded by the ARM SoC and pushed out over HDMI.
This system essentially allows us to output to any device on the planet, irregardless of the endpoint bus (HDMI, DisplayPort, and any future inventions) by simply producing the relevant adapter that plugs into the Lightning port. Since the iOS device doesn’t care about the hardware hanging off the other end, you don’t need a new iPad or iPhone when a new A/V connector hits the market.
Certain people are aware that the quality could be better and others are working on it. For the time being, the quality was deemed to be suitably acceptable. Given the dynamic nature of the system (and the fact that the firmware is stored in RAM rather then ROM), updates **will** be made available as a part of future iOS updates. When this will happen I can’t say for anonymous reasons, but these concerns haven’t gone unnoticed.
