Both, with a nuance. The AVR simulator syncs to wall-clock time and each frame calculates cycles from real elapsed deltaMs, so delay(1000) takes 1 real second and timer-dependent code (PWM, millis()) runs at correct real time rates. The RP2040 and ESP32-C3 simulators use a fixed cycles-per-frame budget (125MHz/60 and 160MHz/60 respectively), which targets real time but doesn't compensate for frame drops . if the browser stutters, emulated time stretches slightly. All three are cycle-accurate at the instruction level though, so the logic and peripheral behavior is faithful to real hardware regardless of frame timing