https://foxborne.com/blog Source-level write-ups for reliability and flight test engineers. en-us https://foxborne.com/blog/three-clocks https://foxborne.com/blog/three-clocks Sat, 26 Sep 2026 12:00:00 GMT Time and clocks A PX4 flight log counts from boot, the companion journal keeps wall time and the ground station logs arrival. Give each an explicit error bound, and you know which events you can put in order and which you cannot. https://foxborne.com/blog/reading-an-oom-kill https://foxborne.com/blog/reading-an-oom-kill Sat, 26 Sep 2026 12:00:00 GMT Companion computers The kernel’s out-of-memory report names the thread that asked, the process it killed and every page it counted. systemd then records the unit’s result, and two settings decide what happens next. https://foxborne.com/blog/bindsto-mavlink-router https://foxborne.com/blog/bindsto-mavlink-router Sat, 26 Sep 2026 12:00:00 GMT Companion computers A dependency in the unit graph can silence telemetry with no radio fault at all. Here is how to spot one in the journal, and how to prove it on the bench before anyone swaps a radio. https://foxborne.com/blog/telemetry-gap-not-radio https://foxborne.com/blog/telemetry-gap-not-radio Sat, 26 Sep 2026 12:00:00 GMT Ground links A hole in the ground receive log proves only that nothing arrived. A stopped router, a radio that left the USB bus and a berm all look the same there, and other logs tell them apart. https://foxborne.com/blog/cui-on-page-one https://foxborne.com/blog/cui-on-page-one Sat, 26 Sep 2026 12:00:00 GMT CUI and handling The government-wide rule asks for the same banner on every page and a designation indicator on the first. DoD practice prints plain CUI at top and bottom and moves the codes and a point of contact into a five-line block. https://foxborne.com/blog/irig-106-for-px4-people https://foxborne.com/blog/irig-106-for-px4-people Sat, 26 Sep 2026 12:00:00 GMT Flight test A range recorder stamps every packet with a 48-bit counter that ticks at 10 MHz, and it records absolute time as a channel of its own. If you can put a ULog on UTC, you already know the method. https://foxborne.com/blog/jet-speed-clock-error https://foxborne.com/blog/jet-speed-clock-error Sat, 26 Sep 2026 12:00:00 GMT Flight test At 170 m/s, a ±40 ms clock bound is ±6.8 m of track; on a quad it is ±0.48 m. Draw it along the track, and you can see when a log cannot say which side of a line an event fell on. https://foxborne.com/blog/px4-link-loss-timer https://foxborne.com/blog/px4-link-loss-timer Sat, 26 Sep 2026 12:00:00 GMT PX4 internals COM_DL_LOSS_T does not start at the last heartbeat. It starts at the last status report that still carried it, which on a real vehicle adds one and a half to almost four seconds.