Arm Cortex Expert

This one's for anyone writing firmware for ARM Cortex-M chips like Teensy 4.x, STM32, nRF52, or SAMD. It covers the full stack: peripheral drivers, DMA setup, interrupt handling, and the critical stuff like memory barriers and cache coherency on M7 cores that will bite you if you get them wrong. The safety-critical patterns section is gold, especially the explanations around MMIO barriers and DMA buffer alignment. You'll get complete driver implementations, not snippets, with the kind of annotation that explains why a register write needs a barrier or why your buffer corrupts adjacent memory. If you're debugging intermittent failures that vanish when you add print statements, this skill knows exactly what's happening.