cuckoo-escapement/dashboard/deploy/caddy-affinity.conf

# systemd drop-in: /etc/systemd/system/caddy.service.d/affinity.conf
#
# Keep Caddy off cpu0. The PPS interrupt is handled there and cannot be moved
# (Pi 4 GPIO IRQs are demuxed via pinctrl-bcm2835 and refuse an smp_affinity),
# so any work scheduled on cpu0 adds jitter to the PPS timestamp directly.
# Caddy is mostly idle, but on this box cpu0 belongs to the clock. See
# TIMING-NOTES.md.
[Service]
CPUAffinity=1
Nice=10
The Cuckoo Escapement: field report, kernel patch, dashboard 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) 2026-07-14 09:21:25 -06:00			`# systemd drop-in: /etc/systemd/system/caddy.service.d/affinity.conf`
			`#`
			`# Keep Caddy off cpu0. The PPS interrupt is handled there and cannot be moved`
			`# (Pi 4 GPIO IRQs are demuxed via pinctrl-bcm2835 and refuse an smp_affinity),`
			`# so any work scheduled on cpu0 adds jitter to the PPS timestamp directly.`
			`# Caddy is mostly idle, but on this box cpu0 belongs to the clock. See`
			`# TIMING-NOTES.md.`
			`[Service]`
			`CPUAffinity=1`
			`Nice=10`