ESP32: RTC and Low power mode

https://www.espressif.com/sites/default/files/documentation/esp32_datasheet_en.pdf

3.3 RTC and Low-power Management

3.3.1 Power Management Unit (PMU)

With the use of advanced power-management technologies, ESP32 can switch between different power modes.

 

• Power modes – Active mode

The chip radio is powered up. The chip can receive, transmit, or listen. – Modem-sleep mode: The CPU is operational and the clock is configurable. The Wi-Fi/Bluetooth baseband and radio are disabled. – Light-sleep mode: The CPU is paused. The RTC memory and RTC peripherals, as well as the ULP coprocessor are running. Any wake-up events (MAC, SDIO host, RTC timer, or external interrupts) will wake up the chip. – Deep-sleep mode: Only the RTC memory and RTC peripherals are powered up. Wi-Fi and Bluetooth connection data are stored in the RTC memory. The ULP coprocessor is functional. – Hibernation mode: The internal 8 MHz oscillator and ULP coprocessor are disabled. The RTC recovery memory is powered down. Only one RTC timer on the slow clock and certain RTC GPIOs are active. The RTC timer or the RTC GPIOs can wake up the chip from the Hibernation mode.

 

* RTC / RTC Memory

RTC memory refers to a small, low-power memory section in microcontrollers that remains powered during deep-sleep mode to retain its contents. This is essential for applications that require data persistence through power cycles without utilizing battery power for larger memory units. The RTC (Real-Time Clock) memory is typically used to store critical data that must be quickly accessible upon waking the processor from deep sleep.

Detailed Explanation of RTC (Real-Time Clock)

The Real-Time Clock (RTC) is a computer clock, often in the form of an integrated circuit, that keeps track of the current time. Even though the term often describes devices in computers and embedded systems, its main purpose is to maintain an accurate time count. The key features of an RTC make it crucial for various applications:

1. Timekeeping: It keeps track of the accurate time, which includes hours, minutes, seconds, and often the date including year, month, and day.
2. Battery-Operated: It is typically powered by a small, long-lasting battery that keeps the clock operational even when the main power is turned off. This feature is critical in systems like PCs, servers, and embedded systems where time needs to be maintained accurately regardless of system power state.
3. Low Power Consumption: RTCs are designed to consume minimal power, making them efficient for use in battery-operated devices like wearables and mobile phones.
4. Alarm Functions: Many RTC units come with built-in alarm capabilities that can trigger events at specified times. This is useful for scheduling activities that require action at a particular time, such as waking up a device from sleep mode.
5. Time Stamps: In systems that log data, RTCs provide a timestamp for each entry, enabling a reliable and accurate timeline of events. This is crucial for debugging systems and tracking event history.
6. Network Synchronization: RTCs in some devices can be synchronized with network time protocols, ensuring that they maintain accurate time that aligns with world clocks. This synchronization is essential for applications that require coordinated timing across multiple devices, such as in telecommunications and internet data operations.

Overall, RTCs are fundamental in a wide range of applications, providing essential timing and synchronization capabilities that enhance the reliability and functionality of technological systems. In the context of ESP-IDF and similar embedded frameworks, RTC functionality allows for efficient power management and reliable operation under constrained power conditions, enhancing the performance and versatility of embedded applications.