So instead of just going with USB3 like other phone manufacturers and having native HDMI they created their own interface that results in an a picture display with noticeable artifacts.
What's USB3 got to do with HDMI?
The Lightning Digital AV Adapter Surprise
21–30 of 85 posts
Re: The Lightning Digital AV Adapter Surprise
#22Earlier quoted context omitted.
I honestly don't know. Someone is somehow implying that the adapter is implementing a full stack capable of being an AirPlay receiver and transcoding video on the fly. I think Cabel is wrong or has explained what they think is occuring incorrectly. /shrug
In this case, AirPlay is our easier-to-understand way of saying "the results you're getting are exactly the same as when you stream iOS video using AirPlay". (Which is really weird for a video-out dongle! Especially since the former, non-Lightning one did proper video out.) I've tweaked the post to make it clearer that AirPlay isn't _necessarily_ the _exact_ mechanism being used! It could just be H.264 or MPEG or wha…
> Mostly I'd love to know exactly what this chip/system does, so if anyone here with far more advanced hardware knowledge than any of us have feels up to hacking around, that'd be amazing! :)
Its converting an encoded steam to HDMI output. There aren't enough pins on a lightning connector to directly output HDMI and even if it could, you still need a transceiver somewhere (not particularly trivial in terms of space or power to stuff in the phone).
The SoC is most likely a little ARM core to manage stuff (Cortex-M0/3) with a video decoder and HDMI transceiver, the 256MB of ram is there primarily for the decoder to use. It also needs to mux the audio stream into the HDMI encoding.
As for 'it runs iOS', your really splitting hairs, its pretty normal for the master devise to load a slave device with its firmware when plugged in (rather than storing the firmware in flash on the slave). The fact that they would use some knocked down version of iOS isn't terribly surprising. Embedded versions of more powerful OSs are used all the time; There is a non-zero chance your stove and microwave are 'running linux'.
Re: The Lightning Digital AV Adapter Surprise
#23I think they're way off on the theory the cable is running iOS. I think what's most likely is the phone is putting out a h264 stream and the chip is just decoding it. Rather than a whole ios stack & AirPlay protocol. Sure this shares some similarities with how AirPlay works (showing a h264 stream from the device ) but wouldn't require a whole system on a chip just for showing this feed.
Why not? AirPlay is a pretty high-level protocol, and it's got an ARM SoC, so the natural thing for Apple to do would be to use the ARM version of XNU with a minimal userland that has their AirPlay implementation and whatever codecs it needs.
At least, If someone handed me one of these dongles with a copy of the protocol spec and asked me to write the software for it, I'd do something similar except using Linux. (Sidenote: buildroot is great for creating embedded systems running Linux.)
Re: The Lightning Digital AV Adapter Surprise
#24Apple says the adapter can play 1080p video.
Is it possible that it could play 1080p video, but the on-device encoding is limited to 1600x900, so can't mirror at 1080p?
Re: The Lightning Digital AV Adapter Surprise
#25Most cables that adapt signals from one format to another are 'active' (that is, contain a microcontroller). c.f.: https://en.wikipedia.org/wiki/Active_cable
I think what makes this particular dongle odd is that unlike most active cables, which contain just a encoder/decoder chip, Apple has put a full ARM SoC.
Re: The Lightning Digital AV Adapter Surprise
#26Maybe it's a chip to prevent the cable from being used to display any 'barely legal teens'.
Re: The Lightning Digital AV Adapter Surprise
#27So instead of just going with USB3 like other phone manufacturers and having native HDMI they created their own interface that results in an a picture display with noticeable artifacts.
What's USB3 got to do with HDMI?
Most non-Apple smartphones have micro-USB ports for charging, and most made in the past few years also support sending an HDMI signal through this port, either via MHL [1] or SlimPort (notably, Nexus 4). All it takes is a $10 adapter cable rather than a $40 SoC transcoding things.
1: http://en.wikipedia.org/wiki/Mobile_High-Definition_Link#Mob...
Re: The Lightning Digital AV Adapter Surprise
#28Earlier quoted context omitted.
What's USB3 got to do with HDMI?
Most non-Apple smartphones have micro-USB ports for charging, and most made in the past few years also support sending an HDMI signal through this port, either via MHL [1] or SlimPort (notably, Nexus 4). All it takes is a $10 adapter cable rather than a $40 SoC transcoding things. 1: http://en.wikipedia.org/wiki/Mobile_High-Definition_Link#Mob...
They also have hardware in the phone to generated HDMI (although electrically modified to fit on the USB connector). Given that only a tiny percentage of people will ever plug their phone into HDMI, it makes sense to have that minority pony up $40 instead of making everyone pay an extra dollar for the hardware they will never use.
Re: The Lightning Digital AV Adapter Surprise
#29Earlier quoted context omitted.
Actually, they're dead on. (And no, I won't corroborate that further. But it does download a stub copy of iOS.)
This provides no useful information whatsoever. I wouldn't be hugely surprised if they wrote code to the ARM MCU (if it has 2GB of RAM to work with), but what does "stub copy of iOS" even mean? Also. Jimmy Hoffa is buried inside that microcontroller. I won't corroborate this further, but this is the dead-on truth.
No need to be sarcastic. I find it interesting that somebody goes through the trouble of creating a new user account, just to confirm a theory that nobody could confirm without getting in trouble.
It doesn't prove anything, but it certainly fits the context. I would say the theory (and the extra bit of information) merit being analyzed further.
FWIW, a "stub copy of iOS" would mean in this context "a copy of iOS where every OS function is stubbed except what's necessary to run AirPlay."
Re: The Lightning Digital AV Adapter Surprise
#30One must wonder why they chose to expend significant R&D to make a complicated, power-sucking adapter for use on a mobile device that provides sub-par output and costs quite a bit more than a "dumb" cable.
Maybe I'm missing something, but I feel like Lightning is just the next Firewire without all the usefulness that FW had (low latency, dedicated bus that wasn't USB, lots of pro audio gear that worked with it, ability to daisy-chain, faster real-world speeds than USB, near-ubiquity before FW800 came out, super small form factor (the 4pin is tiny; not much bigger than a lightning)).