[Freedombox-discuss] Android stick-PCs as a potential Commotion/FreedomBox/OpenWRT platform?

[Paul Gardner-Stephen]

Hi all,

Sorry if you have already thought about and discussed these devices, but
they strike me as potentially very interesting for both communities, in
addition to our own interest in them for the Serval Project.

We have been looking at some of the cheap Android-based stick PCs as a
possible platform for Serval Mesh Extenders, such as the MK802ii and more
recent MK808B.  For more about the Mesh Extenders and their long-range UHF
packet radios, refer to:

http://developer.servalproject.org/dokuwiki/doku.php?id=content:meshhelper:main_page&#prototyping


or:

http://servalpaul.blogspot.com/2013/02/building-serval-mesh-helper-device.html

and subsequent posts to that blog.

The newer generations of the Android stick-PCs have dual-core 1.5GHz ARM
processors, 1GB of RAM and 16GB of flash, dual-antenna 802.11n Wi-Fi
(although the firmware is not ideal, more on that later), USB host port,
microSD slot, and HDMI out, all in a tiny thing about 80mm x 35mm x 15mm
depending on the particular variant you get.  You get all that for under
US$50, e.g., from geekbuying.com.

These typically come with a root-enabled ROM, and are very easy to flash
with a complete new operating system.

Thus compared with many wireless routers they have much greater CPU and
memory resources, and similar or lower cost.

What I wanted to discover what their power consumption was, because I want
to run them off battery for really resilient deployments.

While I was initially concerned about the power consumption, I discovered
that the later generation models can perform useful services, including
running Wi-Fi for about 1W:

http://servalpaul.blogspot.com/2013/04/comparing-energy-consumption-of.html

The main issues that I have identified are likely to be:

1. The Wi-Fi antenna are little patch antenna, which probably don't have
that great performance.  They could be replaced fairly easily though, I
suspect.  On the up-side, they do have two antenna for doing clever 802.11n
things.

2. The Wi-Fi firmware that comes with the ROMs I have found don't include
simultaneous AP and ad-hoc capability, at least as far as I can tell.  This
would need investigation.  They apparently use a Broadcom 8330 based Wi-Fi
chipset in at least some variants, which leads to my next point.

3. The Wi-Fi chipset and design quality varies between suppliers of these,
as it appears that they are all using a reference design of the RK3066
chipset, to which they add Wi-Fi.  Some use realtek or mediatek chipsets
instead of broadcom.  Some implementations are better than others, e.g.,
some sub-optimal implementations seem to have a common ground-plane between
the Wi-Fi and USB, which reduces the sensitivity of the Wi-Fi receiver. All
this is both a negative and positive. On the negative side, some variants
might be complete duds for our desired use-cases.  On the positive side, it
might be possible to encourage one of these manufacturers to make one with,
for example, an Atheros Wi-Fi chipset that is well supported by Linux,
OpenWRT and Debian.  Related, I have yet to survey the complete OS image to
see if there are any other closed binary blobs hiding around the place.

4. There is no on-board ethernet port on the cheaper models.  This could be
solved with a USB ethernet adapter, or again, encouraging one of the
manufacturers to make a variant that is better optimised for our
communities needs.

If anyone in the community is interested in working on porting OpenWRT
and/or enabling simultaneous AP+ad-hoc Wi-Fi on these, we can probably
arrange to provide a couple of MK808Bs to facilitate this.

Paul.
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