Category Archives: General

Singer no. 42 Cabinet Swing-Arm

Posted on 2013-12-22 by pappp

One of my previous posts about my Singer attracted an email conversation with another owner about the swing-arm mechanism on the no. 42 cabinet. Unfortunately, the end-of-semester insanity struck before the matter was settled, and I am still unsatisfied with what I’ve been able to figure out.

Now that I’ve had a bit of time, I pulled apart my mechanism and took photos, shared below. I’m reasonably certain that if the mechanism is complete and correct, the arm will automatically deploy when the leaf is lifted. Unfortunately, I’m also quite sure that the pieces I do have are inadequate to support that functionality, and I can only guess what the other bits might be.

The larger diameter end of the part I do have matches the diameter of the holes in the hinge, and the smaller-diameter end matches the hole through the swing arm and base.
My best guess is that there are several objects similar to the pictured pin, one of which protrudes below the table into the catch hole of the swing arm through the holes in the hinge mechanism, springloaded “up” such that it retracts when the leaf is out, and is depressed by something protruding from the hinge-hole in the leaf pinning the arm when closed. The pictures sent by the other owner show what looks like the end of a similar pin protruding into the bracket, but it does not extend any where near far enough to retain the arm.

Posted partly in the hopes that my pictures will help other folks with their cabinets, but also if anyone with a no. 42, especially if it has a working swing-arm mechanism or parts that are not pictured, sees this I’d love some more information about how they’re supposed to go together.

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Heterogeneous System Architecture

Posted on 2013-11-23 by pappp

Post-SC, I sat down to do some deeper reading on the HSA (Heterogeneous System Architecture) stuff. This is AMD/ARM (and many friends)’s plan for the future, and it is pretty fucking exciting (in an obscure technical sort of way).

The best starting point I found is this year old whitepaper [PDF warning]. They’re using slightly odd terminology, the important bits are LCU = Latency Compute Unit = Conventional MIMD CPU Core, TCU = Throughput Compute Unit = Accelerator, typically SIMD-engine-ish like a GPU, HSAIL = HSA Intermediate Language = IR that can be compiled at install/run time to accelerator’s ISAs. The hardware-side implementation details are nowhere to be found, but there are a lot of seriously exciting model-affecting things detailed on the software side. The general model, with things broken into grid, work group, work item, wavefront is FAR more sane than most of the parallel schemes (I’m thinking specifically of the awful CUDA nomenclature). Internally, the exciting stuff includes requiring a limited sort of preemption on the accelerators, a relaxed consistency model across memory shared over a whole system (nice thread-like shared memory), an intermediate low level language/VM for portability, and assurances about barrier capability in the TCU. The actual objects are basically FAT ELFs with a complete copy of the program for the LCU, plus the HSAIL representation for the parts that can be shipped to TCUs. I’m pleased that there seems to be a clever run-time that does a bunch of platform enumeration and controls where parts run in a rule-automated-but-overrideable way.

I had some folks at SC tell me they’d try to get me a more implementation-focused whitepaper on the hardware side at AMD but they weren’t sure if/when details would be clear for distribution. On the software side, the details are in a published draft of the ISA/Model/Compiler Writer’s Guide that I browsed around in a bit and found very enlightening. The reference tool-chain seems to be mostly built on LLVM and OpenCL.

I have some other SC-related thoughts to share, but I want to get them a little bit more refined (and decide which are for public consumption) before I post.

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SC13

Posted on 2013-11-15 by pappp

I will be at SC’13 November 16-21 with the aggregate.org/University of Kentucky research exhibit again this year in booth 629. Media and impressions should appear somewhere in my ‘net presence during and after the conference, it is always a good show.
Edit:Pushing photos from the show floor into this album.

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chdk-ptp PKGBUILD

Posted on 2013-11-10 by pappp

In another episode of fixing things for the Cameras as Computing Systems class I’m taking, I made a PKGBUILD that apparently correctly builds and installs chdk-ptp on Archlinux systems. Chdk-ptp is a tethered-control application for Canon cameras running CHDK, that hooks a variety of custom extensions to the ptp protocol. Their build system is a little lackluster, is missing things like an install rule, and requires a helper script be installed to do some path munging before running the binary, but the documentation is good enough to sort it out, and the program itself seems to work. My package depends on iup-all-bin from the AUR which also provides the cd dependency (not marked in its provides array, though there isn’t an official package to conflict with). I tried to use the built-from-source AUR packages for cd (Seriously, who thought that was a good name for a piece of software?) and iup, but iup was giving me a hassle and the chdk-ptp documentation suggests the binary distribution will be less trouble anyway.

The PKGBUILD format has changed a bit since I was last making my own- I like most of the changes in terms of clarity and modularity, but it does require a bit of re-learning. It also means I have a couple of pet packages that probably need attention.

The build is a little janky so despite it passing through namcap with only one expected warning, I don’t want to put it in the AUR until I’ve tested it enough to be reasonably sure it works as intended. I expect I will get around to that eventually.

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Gigabit to The Home BoF Opening Presentation

Posted on 2013-11-01 by pappp

I gave the discussion-starting talk for this week’s CS departmental BoF session. The topic this week was “Unlimited Internet bandwidth – Would it be a game changer or no big deal?” My opening talk was just to get people up to date on the current events to kick off a discussion, though it is very similar to asking “What will we do with the internet” in the early ’80s, and thus rather difficult to suggest up plausible cases that aren’t “The same thing but faster.”

Callout:

Gigabit to the home is rapidly becoming a reality. Programmable hundred gigabit networks are already being constructed. Cellular networks are improving so fast that people are dumping their wired connections in favor of wireless. In short, networks are becoming so fast that one can begin to imagine a world where bandwidth is essentially unlimited.

But how would the world change if we had (essentially) unlimited bandwidth to everywhere? Would it change anything? Don’t most apps already have all the bandwidth they need? Aren’t networks already fast enough to support “the Cloud”? Have we already max’d out on bandwidth? Are there any super-cool apps that could still be enabled by even faster networks? If so, what are they? Will they be truly radical, or just an incremental improvement?

Come and find out at our next CS Bof, Friday, Nov 1 at 3pm when we will debate whether there are apps that will benefit from even faster network speeds. If there was unlimited bandwidth, what new apps could *you* see emerging? Join us Friday to dream about the possibilities and give your opinion.

Slides , Notes

In a related note, I’ve made slides for several presentations recently in Beamer, including this one, and I’m pretty convinced I’m never voluntarily using Powerpoint or any obstinate WYSIWYG slide system again. Beamer is a superior tool for the job for every kind of presentation using slides I’ve ever run into.

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Makergear M2 Heated Bed Issue

Posted on 2013-10-04 by pappp

There was a problem with the Lab’s Makergear M2 recently that is worth writing up.

Last weekend, we had it off site for a demo event for a group of highschoolers interested in engineering and medicine, which included assembling samples of these printable articulated hands that Dr. Dietz designed. (Semi-related: I’ve watched him do it, and continue to be mystified how he does things like this in OpenSCAD). We printed some models live, but on the last print of the trip it made a burning plastic smell. Not the usual, pleasing corn-syurp-y PLA-at-work smell, but acrid recently-deceased-electronics smell. We couldn’t locate the problem, and everything was working, so we assumed filament impurity and moved on.

M2RAMBO39530Melted

The next day, the bed stopped heating. Probing around with a DMM indicated the board was fine but the wire harness was not (A thank you to the Ultimachine folks for putting proper test points on the outputs). A bit of googling turned up this thread implicating the quick release screw terminal block that connects the bed leads to the board. Sure enough, upon yanking the connector free, the removable wire-side portion was a melted mass.

39530Melt

The existing connector is a Molex 39533-2002 rear-entry, two lead “Eurostyle” connector. Interestingly, Makergear and/or Ultimachine (Makergear buys and installs RAMBO Boards) used straight-through 5.08mm (200mil, but usually talked about in metric) quick release connectors – screws on the top, wires enter from the right – for the other MOSFET outputs, but a rear-entry (screws on the left, wires enter from the top) for the bed heat. This seemed odd since the side of the little laser-cut enclosure the RAMBO board lives in obscures the screw heads, but the reasoning will become clear. When I was poking at it to see if I could figure out what went wrong, I noticed the threads on the melted side were all but stripped out, but I don’t know if that was a cause or a symptom.

M2RAMBO39533

Since it is a standard connector, the (apparently intact) board side will mate with any two-position 3953x part. We found an ebay listing for five 39533-2002 for about $8 shipped, which are compatible and straight-through. Sadly, ebay is usually cheaper and faster than dealing with an electronics vendor if you only need one thing. The replacement seems to work fine, but clearly the original was a rear-entry model to keep the wires from being pressed against the side of the case. The M2’s wire harness is definitely its weak point; two of three serious intervention-requiring stoppages have been related to the bundle headed up to the bed/Y assembly.

The general lesson is to keep an eye on your screw terminals, especially if they are carrying current. I recall replacing the (non-quick-release) bed heater screw terminals on Collexion’s Makerbot ToM after a meltdown not long ago, so there is clearly a general issue with running that much current through screw terminals (several of the common crimped connectors would likely be superior in most ways). Since it came up (and since it is intuition-defying and I’ve heard a lot of people who should know better get it wrong) I’ll close with a reminder that you should not tin your wires before placing them in screw connectors – I know I’ve read this in a standard, research-backed source from ISO or NASA or somesuch, but I can’t find it right now.

ADDENDUM: It cooked two more of the same connector, then we discovered that the SD card connector was a little lose, and apparently causing a ground problem. It hasn’t cooked another connector since, and the bed heats faster than it was, so strong evidence that that was the root cause.

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As a quick “look at me being a good citizen,” a “class projects sometimes do have positive externalities,” and so that I have a convenient pointer/local copy, I just touched up the script for building a GCC 4.5 toolchain suitable … Continue reading →

Posted on 2013-10-01 by pappp | Leave a comment

Fall 2013 Impressions

Posted on 2013-09-09 by pappp

Following my habit of posting Before/After notes on my semesters, some impressions for Fall 2013 now that every class has met. I’m getting to the point where the bulk of coursework I can and would sign up for tends to be special topics courses, which is a very interesting, if sometimes strange, phenomenon.
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Udisks2 Misfeature Fix

Posted on 2013-08-25 by pappp

Apparently David Zeuthen committed a patch back in February (appears in udisks2 >= 2.0.91, afik) that lets you single-point (or selectively) switch Udisks2 back to the nice, sane, predictable “Removable drives mount to /media” behavior instead of the asinine “Drives are owned by some user who happens to be logged in at a local session at the time they are plugged, mounted to /run/media/$USER/$LABEL, and ACL’d to that user” nonsense that has been a near-constant source of inconvenience lately. I’m surprised it took me this long to find it.

Following these instructions, all you have to do is create a Udev rule (ie. /etc/udev/rules.d/99-correct-media-mount-point.rules) with the line ENV{ID_FS_USAGE}=="filesystem|other|crypto", ENV{UDISKS_FILESYSTEM_SHARED}="1", and storage mounts to /media/$LABEL (You may want to leave out crypto, it actually makes sense for encrypted volumes to be obscured from other users like that) with no funky ACLs by default.

No more tedious user,noauto,nofail fstab entries on all my machines, for all my frequently-used discs to prevent that behavior! Hurrah!

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The Best Science Fiction and Fantasy of The Year Vol. 7

Posted on 2013-07-18 by pappp

While I’m writing up things I’ve done recently, I finished this year’s edition of the Jonathan Strahan edited The Best Science Fiction and Fantasy of the Year collection. As in previous years I’ll mention the high points.
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