The amplitude should be less than 1.2 V for sine wave signal and less than 1 V for square wave signal. The external clock signal must be connected to the 32K_XN pin. This source provides a better frequency stability at the expense of a slightly higher (by 1 μA) Deep-sleep current consumption.Įxternal 32 kHz oscillator at 32K_XN pin: Allows using 32 kHz clock generated by an external circuit. However, the frequency stability of this clock source is affected by temperature fluctuations, so time may drift in both Deep-sleep and Light-sleep modes.Įxternal 32 kHz crystal: Requires a 32 kHz crystal to be connected to the 32K_XP and 32K_XN pins. Internal 150 kHz RC oscillator (default): Features the lowest Deep-sleep current consumption and no dependence on any external components. The RTC timer has the following clock sources:
However, users can also select a different setting via the CONFIG_NEWLIB_TIME_SYSCALL configuration option. It is recommended that users stick to the default option as it provides the highest accuracy. The possible combinations of hardware timers used to keep system time are listed below: Time will be measured at 1 μs resolution. The timer uses the APB_CLK clock source (typically 80 MHz), which has a frequency deviation of less than ☑0 ppm.
High-resolution timer: This timer is not available in sleep modes and will not persist over a reset, but has greater accuracy. The frequency deviation depends on the RTC Timer Clock Sources and affects the accuracy only in sleep modes, in which case the time will be measured at 6.6667 μs resolution. RTC timer: This timer allows time keeping in various sleep modes, and can also persist time keeping across any resets (with the exception of power-on resets which reset the RTC timer). System time can be kept by using either one or both of the hardware timers depending on the application’s purpose and accuracy requirements for system time. ESP32 uses two hardware timers for the purpose of keeping system time.
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