JR · @dniminenn
I build things that have to be measurably correct.
Notes on precision timing, audio, embedded systems, and debugging by measurement. Most of these started as an idle question and ran further than they had any right to.
Precision timing
GPS-disciplined clocks, NTP and PTP, nanosecond budgets, and proving a clock is honest.
Audio, end to end
Bit-perfect playback paths, DSP, LED visualizers, and chasing latency you can hear.
Embedded systems
ESP32, RP2040, and the firmware that has to keep running when the network does not.
Systems debugging
Reading the kernel, tracing the wire, measuring instead of guessing.
Selected writing
Relaying a self-hosted mail server through Cloudflare
A personal mail server can receive on its own, but sending needs a relay with a reputation. Mine was rewriting my links and adding tracking pixels. Cloudflare now sells a plain SMTP relay on the five-dollar Workers plan, and the cutover is one token, six postconf lines, and a bounce domain Cloudflare maintains for you.
Swapping a live router in 50 milliseconds
Two VyOS VMs with identical MACs, a bridge with no ports, host-side tap moves, a seeded DHCP lease, and a dead-man switch. How a home router gets cut to a new release while the house sleeps.
The clock that rang like a bell under load
I built a PRU clock that held nanoseconds on the bench, then rang under load. The daemon crossing its ticks into CLOCK_REALTIME was modeling chrony's own steering and feeding the model back. I fixed it by moving the reference out of userspace, into a Linux PTP hardware clock.
Reverse engineering the Attack Shark keyboard protocol
Attack Shark, Epomaker and Akko sell hundreds of keyboards built on the same ROYUAN hardware, configurable only through Windows software. Here is the wire protocol: two colliding command sets, per-key colour that lands in flash, and a firmware image read out of a rescued binary.