[time-nuts] looking for low-power system for gps ntp timekeeping

Attila Kinali attila at kinali.ch
Mon Jul 1 16:47:36 EDT 2013


Although quite a bit OT, i would like to coment a bit on the topic of
application processor boards, as there seem to be a lot of handwaving
in this area.

On Mon, 1 Jul 2013 08:14:55 -0700
Chris Albertson <albertson.chris at gmail.com> wrote:

> Thanks.  I didn't know there were two kinds.  This is more useful for only
> $5 more.

There are actually 4 kinds of the beagle family:
Beagle Board
Beagle Board xM
Beagle Bone (White)
Beagle Bone Black

The Board and Board xM are more of the "let's replace a PC" kind of design,
while the two Bone variants are more experimenter, development boards,
similar to the idea of arduino.

A word on the different boards there are out there:
Please keep in mind that most of these boards are using CPUs designed
for other uses than most people will use them for. the Beagle Board and
the Beagle Bone White use processers that orignally come from wireless
(aka cell phone and similar stuff) business. While the xM and the Black
use one from the industrial division. You can see that clearly in the
features that they support.

For comparison, the Raspberry Pi CPU was meant for video applications.
That's why you have a humongus GPU whith a tiny CPU attached to it.
The CPU was not meant to run an OS, but to support the GPU. Hence the
weird USB design, where the USB "controller" generates interrupts every
start of frame (aka every 125us) and the CPU has to do every low level
stuff USB needs in software, instead of the hardware doing it (i guess
it was cheaper to design that way). Which leads to a lot of problems when
doing more than just a little bit of communication over USB. It also
explains why an ARM9 processor does not have an hardware ethernet MAC.

Similar things can be said about boards like the cubieboard, which
uses an AllWinner A10, or A20 for the cubie2. These are CPU designed
for tablets and settop boxes.

Thus each of the design has their own set of advantages, disadvantages
and quirks, depending on where the original CPU design came from.

Also keep in mind that you will not run the board without software.
The quality of the software package and how easy it is to customize
is very different for the various boards out there. General rule of
thumb: if lots of people are using it, there is a better chance
to find good support for it. The Odroid/hardkernel boards are a nice
negative example in that regard. Another rule of thumb: being able
to compile the whole software package yourself is not just a nice
feature, it's a must have. Stay away from any board that needs any
binary only stuff or where you cannot compile everything from source.
Also, if you don't get full schematics, that should make you suspicious.
 

HTH

			Attila Kinali

-- 
The people on 4chan are like brilliant psychologists
who also happen to be insane and gross.
		-- unknown


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