https://ragnar-vallhala.github.io/ I build low-level systems, and I read far outside them. Flight stacks and kernels. Philosophy, politics, sociology. The verse below is the closest thing to my method. Do the work fully. Hold the results loosely. en https://ragnar-vallhala.github.io/engineering/i-wrote-an-fft-to-play-music/ https://ragnar-vallhala.github.io/engineering/i-wrote-an-fft-to-play-music/ Tue, 16 Jun 2026 00:00:00 GMT Engineering The browser ate gigabytes to play a song, so I wrote a 2,000-line terminal music player with no pip deps. Along the way it grew a hand-rolled Fourier transform, a filesystem-as-LRU cache, two mpv processes, and an LLM that scores my songs by vibes. A field report on accidental over-engineering. https://ragnar-vallhala.github.io/engineering/does-an-avr-need-simd-a-roofline-study/ https://ragnar-vallhala.github.io/engineering/does-an-avr-need-simd-a-roofline-study/ Sun, 14 Jun 2026 00:00:00 GMT Engineering I set out to design a wide-SIMD coprocessor for an 8-bit MCU. Then I measured twelve real kernels in a validated gem5 model. A roofline analysis talked me out of the vector unit — and pointed at what to build instead. https://ragnar-vallhala.github.io/engineering/teaching-a-drone-to-tune-itself/ https://ragnar-vallhala.github.io/engineering/teaching-a-drone-to-tune-itself/ Sat, 06 Jun 2026 00:00:00 GMT Engineering We built a closed-loop PID autotuner that flies its own experiments in simulation and searches the gain space — eight optimizers, a chatter-aware cost, and two failure modes that looked solved but weren't. A deep dive into the system, the algorithms, and the fixes. https://ragnar-vallhala.github.io/engineering/benchmarking-vaios-against-freertos-zephyr/ https://ragnar-vallhala.github.io/engineering/benchmarking-vaios-against-freertos-zephyr/ Fri, 22 May 2026 00:00:00 GMT Engineering We measured our in-house real-time operating system against FreeRTOS and Zephyr on the same flight-controller hardware — scheduling, IPC, memory, timing, and footprint. Here is the full set of results.