Ryan Malloy
3b505644b2
Rebuilt with KBUILD_BUILD_USER/HOST/TIMESTAMP pinned. Without them the kernel bakes the builder's user@hostname and wall-clock build time into /proc/version, which publishes operator identity in a public artifact and makes the build unreproducible. Pinned, anyone can rebuild and diff the bytes — the only trust story available for an unsigned community kernel. The installer refuses to run on anything but a Pi 4, refuses a mismatched image/modules pair (vermagic failure means no /dev/pps0 on a kernel that otherwise boots fine — silent and miserable to debug), verifies SHA256SUMS, never touches kernel8.img, and leaves rollback as deleting one config.txt line. Boot-tested on the Pi: Stratum 1, 273 ns offset, PPS handler confirmed NOT threaded. Binaries ship as release assets, not in git.
The Cuckoo Escapement
What the Raspberry Pi time-server guides get wrong, and the numbers to prove it.
Docs: cuckoo.warehack.ing
We built a GPS-disciplined Stratum 1 NTP server on a Raspberry Pi 4, followed the published advice, and measured everything. Most of that advice is wrong on this board. One piece of it is wrong on every board.
| Change | RMS offset |
|---|---|
| Baseline | 823 ns |
chrony median filter + prefer on the PPS refclock |
440 ns |
| PREEMPT_RT, as the guides recommend | 2468 ns ← worse |
PREEMPT_RT + our IRQF_NO_THREAD patch |
199 ns |
The one thing worth stealing
kernel/0001-pps-gpio-keep-timestamp-in-hard-irq-under-PREEMPT_RT.patch
PREEMPT_RT force-threads interrupt handlers. pps-gpio takes its timestamp
inside its handler. So the realtime kernel — the marquee upgrade in every guide
— puts a scheduler between the electrical edge and the clock, and triples your
jitter. Four lines fix it.
As far as we can tell this isn't applied anywhere, which means anyone running GPIO-based PPS on a realtime kernel today is silently eating microseconds of jitter with no reason to suspect it. chrony still says Stratum 1. Everything still looks fine.
What's here
kernel/ |
The patch, and how to build it |
dashboard/ |
The live status page (FastAPI + WebSocket, no build step) |
docs-site/ |
The write-up — Astro / Starlight |
n = 1
Every number here comes from one Pi 4 and one GPS module. This is a field report, not a study. We're publishing the method alongside the results precisely so you can check it against your own board rather than take our word for it.
A Supported Systems joint.