18 November
2018

  

International Symposium on Experimental Robotics

I went to the International Symposium on Experimental Robotics where our group had a couple of papers, and I also gave a talk at an associated local workshop.

My colleagues Ioannis and Stergios, with me
My colleagues Ioannis and Stergios, with me
(Click to expand)


ISER people assembled for a picture
ISER people assembled for a picture
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Buenos Aires by day
Buenos Aires by day
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ISER people
ISER people
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Buenos Aires by night
Buenos Aires by night
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Many of the attendees out socializing
Many of the attendees out socializing
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Sightseeing
Sightseeing
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Giving a talk
Giving a talk
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A also gave a talk at an affiliated workshop
A also gave a talk at an affiliated workshop
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People at the outreach workshop
With the organizers at the outreach workshop
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Yiannis giving his talk
Yiannis giving his talk
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Fancy hotel
Fancy hotel
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My colloeagues Ioannis and Stergious, with me
My colloeagues Ioannis and Stergious, with me
(Click to expand)



By Gregory Dudek at | Leave a comment |    
31 October
2018

I had to opportunity to attend the tribute to Louis Dudek, held at the writer's chapel of St. Jax Church in downtown Montreal. He was, of course, my father and a famous Canadian poet, writer, critic and scholar. At the event a plaque was unveiled and a selection of writers and other people gave short presentations or readings, including Michael Gnarowski the organizer, publisher and writer, Bernhard Beutler who studied and translated my father's work, and poet Stephen Morrissey who gave a great presentation and also read a new poem for the occasion.

Stephen Morrissey's
blog
gives more detail and the beautiful text of his speech.













By Gregory Dudek at | Leave a comment |    
16 September
2018

It's too early to be certain, but ICRA 2019 is looking to be a big one, which is what we expected. The number of submissions to RA letters has exceeded previous records, and the number of regular submissions is climbing (see figure), and there are also a few typhoon/hurricane extended-deadline papers to come later.

The plot below shows submissions coming in, but the absolute number is misleading since it fails to indicate papers in the other input streams.


ICRA 2019 submissions
ICRA 2019 submissions
over time as the deadline approaches,
not including RA-letter and delayed papers
(Click to expand)



By Gregory Dudek at | Leave a comment |    
14 September
2018

Extensions for natural disasters

As the ICRA 2019 deadline was approaching, two natural disasters became apparent: Hurricane Florence and Typhoon Mangkhut. How were to to respond? No official standard policy for deadlines extensions due to natural disasters exists in our community, and some sub-communities like SIGGRAPH do not make exceptions in such cases. Worse yet, we don't have a good standard mechanism for monitoring such events. This is especially tricky since hurricanes and typhoons are intrinsically unpredictable and people can also get upset when extensions are given out selectively and without sufficient cause. Moreover, broad extensions cause a whole cascade of downstream problems and deadline changes what can have potentially serious repercussions.

In our case in 2018, we first became aware of Hurricane Florence (due to being contacted several days early on by members whose universities announced closure policies) and shortly afterwards developed a policy to provide deadline extensions for those who were experiencing extreme hardship.

Subsequently, we learned of Typhoon Mangkhut and extended the policy to that event, first informally and then via an official web site update that took some time to propagate.

This seems to have become a somewhat regular issue and ad hoc methods we used a few year ago when our community was much smaller are not adequate. We will have to develop better mechanisms for world-wide monitoring and adaptation to such emergencies.


By Gregory Dudek at | Leave a comment |    
13 September
2018

  

Submissions for ICRA 2019 are coming in.

We created a special policy for people and organizations being hit directly by hurricane Florence. Since that is probably not a huge fraction of our community, we opted for a solution that involves a substantial amount of manual intercession and verification.

I looks like the conference will be far bigger that originally predicted back when we made our bid many years ago. Best estimates from our team and our community at large are currently at about 4,000 people, but with quite a lot of variance.

We have repeatedly scaled up our plans and with the paper deadline imminent, we should finally have a solid estimate of how big the conference will be, although it's still hard to know the ratio of attendees to papers.


By Gregory Dudek at | Leave a comment |    
15 July
2018

Why embedded systems like the raspberry pi should not allow swapping to an SDcard

SDcard and Flash memory errors



SD card corruption and eventual failure is common on embedded systems like the raspberry pi. I've realize there is a lack of consistent and reliable information on this. This post describes the problem and provides solutions.

This post has 3 parts: description of the problem, practical implications, and tricks to disable swap on the raspberry pi and related linux devices. People who just want a solution can skip to part 3.

Description



In our lab we have a range of systems from expensive underwater robotics to small embedded IoT devices all of which use SD card or flash memory. There are modes of operation that are acceptable on a normal desktop or laptop that will gradually degrade and eventually destroy an embedded device after a few thousand cycles of writing to a given cell. Since the damage is gradual, it can easy to overlook the cause during setup and testing, and just blame it on "bad memory."

The root issue is that solid state memory wears out with successive changes to the contents, and this happens on a per-memory-cell basis. Modern SD and flash memory have sophisticated internal algorithms for "wear levelling" that try to reduce the impact and extend the life of the chips, but these cannot eliminate the problem totally, since it's intrinsic to the physics of the devices. Hard disks, by the way, can also wear out, but not generally as a function of the read-write behaviour. The key idea behind wear levelling it to change the physical location used for frequently-changing data, to spread the use.
[ Technical aside: As of 2011, 25nm MLC NAND lasted for about 3,000 write cycles. As of 2018 some sources suggest that single level cell NAND (SLC) can last for 10,000 cycles ]

For normal use, only a small amount of the device is written at a time and if this is moved around the device it can be many years before the flash memory storage wears out. Without wear levelling it's easy to write a malicious program that "burns through" a specific cell in just a few minutes (although OS cacheing policies also try to preclude this).

Note that there are differences between expensive SD cards and cheap ones. These differences include both the robustness of the memory elements themselves, their speed and also the nature of the wear levelling (e.g static vs dynamic).


Practical implications



Normal file IO will take many years to damage a modern (wear levelled) flash device. Swapping, however, can be much more destructive. The issue is that swapping is a mechanism used by the operating system to compensate for insufficient RAM (memory) and is depends on writing large amounts of data to "disk", and sometimes doing it a lot. This heavy usage could damage a flash device like an SD card in just a few months.

Note that swapping to a "slow device" will also make the system run slow, but on the other hand in can preclude a hard crash that could occur if the system runs out of memory.

The commands below require root (or prefix each command with sudo).

Turning off swapping



dphys-swapfile swapoff
dphys-swapfile uninstall


and also (to make it permanent):

update-rc.d dphys-swapfile remove



Turn off swapping temporarily


The following two lines work (or npt) depending on the kind of linxu distribution you have (i.e does it use systemd):

swapoff -a

systemctl disable dphys-swapfile

Totally disable the swapping mechanism for keeps


apt-get remove dphys-swapfile

Aside from swapping, you can also make the entire filesystem read-only that preventing any writes (but also limiting the kinds of things you can do).


By Gregory Dudek at | Leave a comment |    

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