Inside Chromecast

Inside the Chromecast it’s also a simple affair, I took a look at the FCC disclosure for the Chromecast which had internal images up right after the event, and noted inclusion of a Marvell 88DE3005 SoC and AzureWave NH–387 WiFi combo chip. On the backside is 512 MB of Micron DDR3L memory and 2 GB of flash. The antenna for the WiFi combo is printed on the PCB off to the side, there’s no diversity or anything special, just a single PCB antenna.

The Chromecast supports just 802.11b/g/n (2.4 GHz), sadly no 5 GHz is included. That’s somewhat alarming if you’re in an area where 2.4 GHz is congested to the point of being unusable (just about any major urban area), and even more so since streaming applications demand a good QoS for good experience. I have no doubt that 2.4 GHz-only was chosen for cost reasons here, but I would’ve gladly paid $5–10 more for 5 GHz and eliminating that as a potential problem.

Best I can tell, the Marvell 88DE3005 is a cut down, perhaps binned version of the 88DE3100 SoC that has shipped in Google TV for some time now with just a single CPU core enabled. Some hacking done by enthusiasts has confirmed from /proc/cpuinfo that only a single core is visible to the OS, and that the Chromecast also interestingly enough really runs Android, not Chrome, and includes a build.prop file like you’d expect an Android device to.

Google no doubt chose this Marvell SoC in part thanks to the presence of hardware VP8 decode, and I have no doubt YouTube on the device brings down VP8 versions of videos when available, and the Chrome tab to Chromecast streaming uses VP8 as well. Of course there’s hardware decode of H.264 High Profile onboard as well for Netflix and other YouTube videos without VP8 versions. Google lists the supported codecs on their Google Cast SDK page.


Under Load

Back when the power situation was unknown and still steeped in conflicting information about HDMI power delivery (again, it can't be powered by MHL-HDMI ports which can supply up to 500 mA at present spec, and HDMI doesn't supply enough current, just 50mA), I set about measuring power. I have a handy USB power meter which sits in line with devices and shows a small graph as well as data on its OLED display. I stuck the meter in line between the microUSB power supply provided with Chromecast, and the Chromecast, and measured around 420 mA at peak while decoding either a 1080p Netflix stream or Chrome tab streamed to it, and around 250 mA at idle. All of those are at 5 V, so at peak the Chromecast draws around 2 watts, at idle around 1 watt. Of course if the Chromecast is plugged into your TV’s USB port, chances are when the TV is off power is cut to USB, so idle really is completely off. It’s obvious to me that Chromecast definitely leverages that hardware decoder for both VP8 and H.264 processing to get these very low power numbers.

Introduction and Hardware The First Mode - Cast SDK
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  • Brian Klug - Tuesday, July 30, 2013 - link

    Roku removed 5 GHz then added it back after they realized what a colossal mistake that was, and costs considerably more than $35.

  • Alketi - Tuesday, July 30, 2013 - link

    Anyone pick up on the model number Easter eggs?

    Chrome cast model #: H2G2-42
    Power plug model #: MST3K-US

    Gotta love Google. :)
  • shwetshkla - Wednesday, July 31, 2013 - link

    plz explain.. :/
  • cbrownx88 - Wednesday, July 31, 2013 - link

    yes please do explain!
  • critical_ - Wednesday, July 31, 2013 - link

    H2G2 = HitchHikers Guide to the Galaxy
    42 = Answer to the Ultimate Question of Life, the Universe, and Everything in H2G2
    MST3K = Mystery Science Theater 3000
  • r3loaded - Tuesday, July 30, 2013 - link

    Chromecast looks nice, but I'm not sure why everyone's raving about it. For me, it's nearly useless. I don't have Netflix, I don't have any media bought off Google Play and there isn't a lot on YouTube that's worth displaying on a big screen.

    What I do have is a mass load of music and ripped Blu-rays (main movie in an MKV container with just the English audio track) stored on my home server, accessible as an SMB share. From what I can gather, I won't be able to play any of my locally stored media on a Chromecast. I don't see why a device that's supposed to do media streaming can't even do something this basic.

    I suppose I can have fun displaying web pages on the TV...
  • JNo - Tuesday, July 30, 2013 - link

    I agree. If it helps, apparently Chrome tabs can play a lot of media file types if you drag them in. You can then use Chrome Tab Casting to view it. However, I can only imagine a significant degradation in quality if the source was a decent quality 1080p file.

    So for me too, this is more of a solution looking for a question.
  • setzer - Tuesday, July 30, 2013 - link

    Well, I have the same "problem", another is that I use subtitles, which means that every time I want to have subtitles on some movie I have to re-encode the movie even if it was in some supported format.
    Also my tv (and well, most recent tvs) already is capable of accessing websites and stream content with DLNA so i'm really unsure what is the point of a device like chromecast...
  • matt30 - Tuesday, July 30, 2013 - link

    It can if you encode it correctly. Chome plays MKVs.
  • setzer - Tuesday, July 30, 2013 - link

    Well, that's the thing, chrome may play mkv's but the chromecast thingie only supports a limited amount of codecs, so unless you have all the streams (audio,video,subs) in a supported format you need to re-encode the streams.
    And if you need to re-encode there is not much of difference between re-encoding for chromecast or to a DNLA supported codec which is probably already supported by your tv.

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