Bookmarks

While not everyone agrees on the installation of wind turbines in their proverbial back yards, one thing not up for debate is that there is a drive to build them bigger, and bigger. Big turbines me…

In-DB Kalman Filter

This is the 13th article that I’ve written lately on NTP and PTP timing with Linux. I set out to answer a couple questions for myself and ended up spending two months swimming in an ocean of nanosecond-scale measurements. When I started, I saw a lot of misinformation about NTP and PTP online. Things like: Conventional wisdom said that NTP was good for millisecond-scale timing accuracy. I expected that to be rather pessimistic, and expected to see low microsecond to high nanosecond-range syncing with Chrony, at least under controlled circumstances.In a lab environment, it’s possible to get single-digit nanosecond time skew out of Chrony. With a less-contrived setup, 500 ns is probably a better goal. In any case “milliseconds” is grossly underselling what’s possible. Conventional wisdom also said that PTP was better than NTP when you really cared about time, but that it was more difficult to use and made more requirements on hardware.You know, conventional wisdom is actually right sometimes. PTP is somewhat more difficult to set up and really wants to have hardware support from every switch and every NIC, but once you have that it’s pretty solid. Along the way I tested NTP and PTP “in the wild” on my network, built a few new GPS-backed NTP (and PTP) servers, collected a list of all known NICs with timing features,Specifically GNSS modules or PPS inputs. built a testing environment for measuring time-syncing accuracy to within a few nanoseconds, tested the impact of various Chrony polling settings, tested 14 different NICs for time accuracy, and tested how much added latency PTP-aware switches add. I ran into problems with PTP on Mellanox/nVidia ConnectX-4 and Intel X710 NICs.Weird stuff. The X710 doesn’t seem to like PTP v2.1, and it doesn’t like it when you ask it to timestamp packets too frequently. I fought with Raspberry Pis. I tested NICs until my head hurt. I fought with statistics. This little project that I’d expected to last most of a week has now dragged on for two months. It’s finally time to summarize what I’ve learned and celebrate The End Of Time.

We have been trying CodeRabbit, let's discuss our impressions.

sh is a full-fledged subprocess replacement for Python 3.8 - 3.11, PyPy that allows you to call any program as if it were a function.

There I was, minding my own business downloading ebooks from my Calibre server to my Kobo Libra 2 via the web browser when I stumbled upon a comment. This comment, courtesy of a now unknown Redditor, briefly mentioned something I’d never heard of. Apparently, Calibre Web, the very service I used to sideload books onto my Kobo, had a built-in Kobo sync feature. I stared incredulously at this comment, and then started to do some digging. I even ventured onto Google to find answers, as DuckDuckGo proved unable to pinpoint the exact information I needed. Sure enough, I found what I wanted, or at least the beginnings of it.

Annotations are complicated. If you’re not careful, hidden annotations can be left in documents and cause embarrassment. And how to recover a PDF that Preview has mutilated.

Shortwave listening and everything radio including reviews, broadcasting, ham radio, field operation, DXing, maker kits, travel, emergency gear, events, and more

is just a simple tool I use to quickly find files matching a search pattern in the current directory. I just figured I’d share it because I end up using it a lot.