A read-only root for Slackware ARM

Sunday 20 April 2014, 16:52

In my last posting I described getting Slackware ARM to boot headless on the ODROID U3 single-board computer, and I said that the next step would be to try to make it handle ungraceful shutdown (power loss) better. I plan to put this board into a Eurorack synthesizer module with no easy access to the microHDMI monitor connection, and SSH over the Ethernet connection as the only access to administrative functions. If, when the power is pulled on it, it comes up on next boot in a state where it requires console interaction to do a step like checking the filesystem before it will accept SSH connections, that is a disaster; I'd have to disassemble the whole module to extract the microSDMI card and replace the OS image. To be useful, the ODROID must be guaranteed or almost guaranteed to survive a power drop and come up SSH-able on the next boot. Ideally, I want pulling the plug on it with no shutdown formalities to be the normal expected way of shutting it down too, not just an error condition from which it can recover. A good journalling filesystem can increase the chance of recovery from occasional accidental power drops, but I think the only way to make routine non-accidental power drops safe is to keep the filesystem mounted read-only - which might be desirable anyway, to reduce wear on the flash memory and prevent its being corrupted by other kinds of accidents. So this posting is about my experiences configuring Slackware ARM on the ODROID U3 to keep its root filesystem read-only.

Slackware on the ODROID U3

Sunday 13 April 2014, 18:20

Our last episode concluded with the discovery that the clip leads I was using to power the ODROID U3 had nontrivial resistance, possibly close to two Ohms for the pair. That's a lot, when one is pulling up to 2A through them from a 5V supply. I switched them for some lower-resistance ones, and the ODROID seemed to behave much better. Between that and a replacement of the Hardkernel-supplied microSD card, I was hopeful that the reliability problems would be much reduced and I could make some progress on the software side of things.

More ODROID adventure, or "Young man, in this household we obey Ohm's Law"

Wednesday 9 April 2014, 20:39

As of last update, I had given up on setting up the ODROID U3 without connecting a monitor to it, and was shopping for a micro-HDMI cable. Here are some further notes

Some notes on the ODROID U3

Sunday 6 April 2014, 20:09

I recently bought a Hardkernel ODROID U3 single-board computer to use in one of my projects. The ODROID U3 is an ARM-based computer capable of running Linux or Android, with Ethernet, USB, microSD, and some other ports that I wasn't planning to use. My plan is to use it for controlling a music synthesizer, with the USB ports used to interface to the synth and a little LCD panel, and the Ethernet port used to talk to other computers. This posting contains some notes on getting it to work.

FontAnvil 0.1

Wednesday 5 March 2014, 08:25

FontAnvil is a script language interpreter for manipulating fonts. FontAnvil is substantially compatible with the PfaEdit/FontForge native scripting language, but FontAnvil is intended for non-interactive use; for instance, invocation from the build systems of font packages like Tsukurimashou. To better serve font package build systems in general and Tsukurimashou in particular, FontAnvil has no GUI and, to a reasonable extent, avoids dependencies on external packages.

Visit the FontAnvil home page.

Don't plagiarize your cover letters!

Monday 10 February 2014, 08:39

The text below pretty much speaks for itself. Bold highlighting and numbered footnotes in [square brackets] are mine; all the rest is as I received it. Some irregularities of spacing and punctuation, visible in the original email, aren't obvious in the HTML. Names of the students are redacted because (after finding several more copies on the Web) I imagine the students are relatively innocent victims of bad advice. Name of the institution not redacted because I hope others who receive such letters and look for them on the Web will be able to easily find this posting.

TikZでマック・ペイントの床しいタイリングを描きましょう

Friday 13 December 2013, 13:09

TeXとLaTeXで画を書いたらTikZは便利とポピュラーです。 みんなはきれいなグラフィクスを作っています。 たとえば、これがtexample.netから一つのクリスマスツリーです。

[クリスマスツリー]

しかし、ただのグラフィクスには興味ありません。 今日は1984年からノスタルジックの画を書きましょう。 マック・ペイントを思い出しませんか? そう…

プリティプリントの試作

Saturday 7 December 2013, 10:07

今年「TeX & LaTeX Advent Calendar」に入りました。 14日に私の書き込みを書きます。 それ前このサーバにGeSHiと言うプリティプリントソフトを備え付けています。 この書き込みはGeSHiのテスト・ポストです。

Firefox mouse copy and paste in Twitter

Wednesday 27 November 2013, 12:41

PROBLEM: Since just before the Twitter IPO, when they changed their site code, mouse copy-and-paste no longer works on Twitter's Web site viewed in Firefox. Where before one could highlight text with the mouse and then middle-button click to paste it somewhere, now that either causes the former contents of the clipboard to be pasted, or the string "witter.com". Copy and paste still works if and only if once uses explicit "copy" and "paste" commands with the keyboard or menu bar, but that is much less convenient, and is annoying to discover on the fly. Observed in several versions of Firefox under Linux; similar problems have been reported with other browser and other operating systems. Problem is specific to Twitter.

SOLUTION: In "about:config," set "dom.event.clipboardevents.enabled" to "false." Explanation below the cut.

Hypergeometric tail inequalities: ending the insanity

Monday 25 November 2013, 17:10

Back in 2009, I posted some notes I'd prepared on hypergeometric tail inequalities to this Web site - mostly so that I could find them easily myself, should I need to in the future. In the years since, that set of unpublished notes has become one of my most-cited works. I'm not sure how I feel about that, but whatever; I have stuck it on arXiv to make future citations easier and increase the chance that they'll spell my name right.