MCU_PIO: generic PIO driver with config-driven program loading,
function-pointer init callbacks, blocking put, and DMA async put.
ws2812.pio written from scratch — 800 kHz, 10 cycles/bit, side-set.
HAL_LED: pixel buffer with intensity scaling, RGB byte order for
RP2040-Zero WS2812 variant. SetColor immediately pushes the strip.
APP_CLSW: rainbow HSV hue rotation on startup (auto-mode). Color
commands (red/green/blue/off/rainbow) stop the rainbow and set the
LED to a static color. Integer-only HSV-to-RGB conversion.
CMake: added hardware_pio link and pico_generate_pio_header for
ws2812.pio compilation. SYS_ECU init sequence updated.