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Espressif ESP32

The ESP32 is Espressif's popular low-cost WiFi and Bluetooth system-on-chip, built around a dual-core 32-bit Tensilica Xtensa LX6 running at up to 240MHz. Xtensa is a configurable RISC-like ISA with a windowed register file (the visible a0-a15 rotate over a larger physical AR file via WINDOWBASE/WINDOWSTART, driven by CALL4/8/12 + ENTRY + RETW), variable-length 24-bit and 16-bit (density) instructions, a shift-amount register with zero-overhead LOOP registers, and PS / EPC1 / EXCCAUSE for exceptions. It integrates SRAM, external flash over a cache, GPIO, UART, timers and an interrupt matrix alongside the WiFi and Bluetooth radios. Here it runs real bare-metal firmware on a from-scratch Xtensa LX6 interpreter — the site's first Xtensa machine.