Casey had some interesting things to say about the RP, so I'm forwarding
his email. Thanks Casey!

Andrew

PS. We're not using the USB at all on the RP, we're just using the
camera interface and the Ethernet, so luckily the USB instabilities
won't hurt us...

-------- Original Message --------
Subject:        Re: [psas-avionics] Raspberry pi adapter
Date:   Wed, 22 Jan 2014 13:18:13 -0800
From:   ~Me <ctr...@gmail.com>
To:     Andrew Greenberg <and...@psas.pdx.edu>

I'll give you my take on some of this, all based on my personal
experiences with Pi's thus far.

[snip]

I have a first run pi, and a later version pi. All of mine are Model B
boards. The model A boards do not have an eth0 header and only one USB
port. The wiki lists that the model B boards have 512 MB of ram, which
is true for the later runs, but the original runs only had 256. From
here on out, i'm only talking about the "B" variant, as I've never
touched an "A":

There are some electrical differences between the inital run (256 MB
RAM) and later versions. There are many articles that touch on this,
here is an example:
http://theiopage.blogspot.com/2012/06/increasing-raspberry-pis-usb-host.html
and the polyfuses they have removed from later variants. This also is
handy in identifying if you have a later or earlier version. I have
abused both versions quite a lot, and have found to have far fewer USB
dropouts on the newer variants of the board.

I have a first gen board hosted for me, and have found many things can
cause these boards to have issues. A power supply of 1A works best. You
can sometimes get away with .7, but save yourself some headache and get
a good 1A. It is worth noting that most everything on the Pi, is on the
same USB bus. Network / SD card / all USB ports (usually a thumb drive).
I have had a lot of issues getting stable, high throughput networking on
a Pi. The Pi has a built in hardware watchdog, use it, but don't have it
watch networking, USB networking won't come up in time and will cause
perpetual reboots with default settings. I have the watchdog setup to
watch for load and lockups, then have scripts running to monitor
networking, first trying to bring the interface back up and if that
fails, reboot. Most of the time, my mode of failure was the ethernet
controller no longer responding and having no way to reset it with out
rebooting. I have used the Pi for torrents, TOR and have let it sit
idle. The first two states will cause it to reset within a week, usually
3-5 days. Idle I have had good luck with it, though after a month it
will still occasionally lock up. Sometimes it recovers, sometimes not.

I have also experienced my thumb drive dropping out of service (have had
this happen with more than one drive make/model) but SD and eth0 still
working.

I found making some changes to the network settings have helped,
(changing the boot/commandline.txt, sysctl and other things listed here
for example: http://elinux.org/Rpi_USB_check-list )

I use a 512MB variant for a home server for e-mail, web (nginx) and
ssh. It works much better than my first gen.

I believe power causes the most issues, then under certain
circumstances, taxing USB with high network usage and high IO the second
most.

I have tried to find data on the Beaglebone Black as to how it is
handling its NIC and storage. I was tempted to move that direction if
the current setup gave me more issues.

I have heat syncs added to both of my Pi's, but the Vreg on the first
gen ran much hotter than the later runs, and I doubt I really need it on
those.

I have ran tests with out of the box settings, as well as overclocked,
though i've never crazy overclocked them, only a mild amount. The tests
were first run with no overclocking as I wanted a baseline before
potentially harming hardware with an OC.

I can take some photos tonight if you want comparisons of layout. I have
noticed there are differences in some pin header locations and how they
are populated between runs.

I'll make it to meetings soon, I promise :)

Thanks,
~Casey

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