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<p>not at all an expert in this area, but relative to the point
about I2C locking the bus and potentially bricking spacecraft
(towards end of notes).......</p>
<p>This is the second time I've heard of this issue, though haven't
directly experienced it myself (though not a lot of experience in
this area).</p>
<p>The other data point on this was from NASA Goddard's Dellingr
project, where they experienced similar I2C issues. in their case
the main computer kept crashing every 45secs right at the point
where I2C drivers were being loaded during the boot process.
Something about the bus being already 'occupied' which was not
expected by the flight computer. The reload of the I2C driver was
just enough that it was resetting the comms watchdog timer on the
EPS (clyde space product), preventing it from triggering a full
spacecraft power cycle (as far as the EPS was concerned, it was
seeing I2C traffic, so 'all was well' from the comms watchdog
perspective). In their case, they were able to command 'constant'
resets for a pass via the CADET radio, which caused the computer
to reset faster than the 45 sec rate (before I2C driver loading)
for the 4min WD window of the EPS. Net result was a full SC power
cycle, clearing the I2C fault. Memory dumps of the crashes
(enabled by the use of NASA's Core Flight System) allowed them to
post-mortem the problem and determine the issue was with the
reaction wheels saturating the I2C bus. They used NASA's cFS
(Core Flight System, open source flight software running on RTOSs
of various flavors) for the main control software which enabled
them to do the memory dump, upload new 'apps' for interfacing with
the reaction wheels, and ultimately develop a workaround to
continue on with the mission.</p>
<p><br>
</p>
<p>I know other groups are looking at CAN as an alternative to I2C
for the main comms bus (google Cubesat Next Generation Bus). Not
sure if this is a good idea or not, how it stacks up to CAN, etc,
but maybe should be considered........I know its heavily used in
automotive applications, so probably plenty of available component
level HW available and probably SW as well, and if implemented
correctly, probably is pretty robust.<br>
</p>
<p><br>
</p>
<p>As far as open source ground software.....COSMOS from Ball
Aerospace appears to be picking up momentum. Its used by many
companies and NASA. We're now using it on our VCC cubesat mission
at VT for the main Command and Control suite. We had to develop
custom parsers for AX.25 / KISS, but the whole thing is written in
Ruby and after the 'learning curve' related to their config files,
its pretty easy to work with and develop custom pieces/modules
for.<br>
</p>
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<p><br>
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<p>-Zach<br>
</p>
<pre class="moz-signature" cols="72">Research Associate
Aerospace Systems Lab
Ted & Karyn Hume Center for National Security & Technology
Virginia Polytechnic Institute & State University
Work Phone: 540-231-4174
Cell Phone: 540-808-6305</pre>
<div class="moz-cite-prefix">On 10/1/2018 7:12 PM, Michelle Thompson
via Ground-Station wrote:<br>
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<div dir="ltr">Please read Hugh's working group report from Open
Source CubeSat Workshop 2018. He will be writing a blog post
about the event shortly!<br>
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<div dir="ltr">-Michelle W5NYV<br>
<br>
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