Hello, here you have the link to the Espressif documentation (manufacturer of ESP32), but as far as I know Pycom firmware doesn't support ULP, so it can't be used. ULP (Ultra Low Power) coprocessor is a simple FSM which is designed to perform measurements using ADC, temperature sensor, and external I2C sensors, while main processors are in deep sleep mode. ULP coprocessor can access RTC_SLOW_MEM memory region, and registers in RTC_CNTL, RTC_IO, and SARADC peripherals. ULP coprocessor uses fixed-width 32-bit instructions, 32-bit memory addressing, and has 4 general purpose 16-bit registers.