Notes on precision timing, audio, embedded systems, and debugging by measurement. Written by JR (dniminenn).
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.
Every seven hours the router's load average hit 1.0 for forty five minutes. CPU was 98% idle. Nothing ran, nothing blocked, nothing was stolen. The culprit was a beat frequency between two five second clocks, and one of them was mine.
Working with an AI on a side project, it felt more authentic and more obviously not human at the same time. That is not what the uncanny valley predicts. A case that the road forks, and that off-axis is the better direction to be heading.
I prepped a music set for a 1500-watt DIY rig and synthesized a missing sub-bass octave into tracks rolled off below 40 Hz. Measure first, fix only what the numbers justify, don't touch anything else.
The storage interface on a production cluster was pulling 4 to 12x more than the public interface where client requests arrive. Getting to a defensible number meant distrusting everything, including my own profiler, which was off by 30x.
An IMAP THREAD command was panicking inside Dovecot's array code. The crash was real, but the comment above it described an optimization that hadn't run in any -O2 build ever shipped. ATTR_PURE turned it into dead code, and the same annotation decided which line showed up in the backtrace.
I wanted a real Ceph endpoint (S3, CephFS, RBD) to test app code against, without a k8s cluster or a single byte hitting my SSD. One container, ~30 seconds, all in RAM. Then the version sweep broke.
I built a GPS-disciplined NTP server on a $20 ESP32 with single-nanosecond internal timing. Then chrony refused to use it. The fix was not in the clock; it was in how I served the time.
Finding an IMAP server's real capacity means driving load from many hosts at once. The hard part isn't generating the load. It's combining their latencies into one honest P99 without lying about it.
A GPS-disciplined NTP server stopped being disciplined, and every monitor stayed green. The giveaway was a freq_ppb value that repeated byte-for-byte across three seconds, which a live servo never does.
I built a Go daemon that drives a music visualizer on a Pi. The frame rate wasn't mine to pick; the LED protocol had already set it. The real work was a latency budget I had to measure before the lights felt locked to the music.
One USB serial port, two programs that both need exclusive access. ts2phc wants RMC-only for PTP clock discipline; gpsd wants everything else. I wrote a demuxer that gives each one a synthetic port shaped exactly the way it expects.
The standard Linux PPS driver timestamps the GPS pulse in an interrupt handler and pays ~20 µs of jitter for it. The BeagleBone has two 200 MHz real-time cores that Linux never touches. I moved the timestamp into one of those, and the clock offset dropped into the low nanoseconds.
Upstream plugin started pulling 320 kbps instead of lossless FLAC, and swapping client IDs did nothing. The access token had frozen its entitlements at mint time, long before any request went out.
A friend's gaming VM hard-reset its Proxmox host the instant a game launched, with nothing in the logs. The cause sat below every layer we kept editing. A power transient at game launch tripped a PCIe fault and reset the box.
An RP2040 furnace controller would freeze at random, always when the WiFi dropped. The culprit was a connectivity probe that opened a TCP connection to decide whether it could open one. A timeout would have hidden it; removing the probe fixed it.
Reading a u-blox GPS over I2C frees the UART, but the I2C interface has no concept of idle. When the module has nothing to send, every read comes back as 0xFF filler. This is the small bridge that turns that into a chrony refclock.
A host scanner that opened a raw socket and a goroutine per host fell over on anything bigger than a /24. The rewrite uses one socket and two goroutines no matter how many hosts, with an ARP fast path and an unprivileged fallback.
A cheap Ecowitt station reports UV and solar radiation that read high and jump around. The repeater that forwards it to Weather Underground smooths and scales those channels first, and never lets a slow upstream API stall the station.
A blockchain hands you an append-only log of transfers in three shapes, behind a rate-limited RPC that rewrites its own recent history. Folding that into a correct balance ledger is the whole job, and most of the ways to get it wrong don't show up for weeks.
Porting a working chain indexer from Python to Rust, where the easy parts get harder and the vague parts get found. Most of what the rewrite bought wasn't speed, it was bugs that stopped being possible to write.