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The Cuckoo Escapement: field report, kernel patch, dashboard

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What the Raspberry Pi time-server guides get wrong on a Pi 4, with the
measurements. The headline artifact is a four-line pps-gpio patch: PREEMPT_RT
force-threads IRQ handlers, and pps-gpio takes its timestamp inside its handler,
so the realtime kernel puts a scheduler between the electrical edge and the
clock. IRQF_NO_THREAD takes RMS offset from 2468 ns to 199 ns.

- kernel/     the patch
- dashboard/  live status page (position hidden by default)
- docs-site/  the write-up (Astro/Starlight, brass, no tutorial section)
This commit is contained in:
Ryan Malloy 2026-07-14 09:21:25 -06:00
commit 6881489bf6
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dashboard/deploy/gpsntp-dashboard.sudoers Normal file
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# Least-privilege: the dashboard user may run ONLY this one read-only command.
# `chronyc -c clients` is privileged (returns "501 Not authorised" otherwise),
# and this is the served-client list the dashboard displays. Nothing else.
gpsntp ALL=(root) NOPASSWD: /usr/bin/chronyc -c clients