Light-sleep is another power saving mode. In Light-sleep mode, CPUs, digital peripherals and most of the RAM are clock-gated, and supply voltage is reduced. Upon exit from Light-sleep, peripherals and CPUs resume operation, their internal state is preserved. By calling esp_err_t esp_light_sleep_start(), application can enter light sleep mode.
This document gives a brief introduction of the ESP32's current consumption during Light-sleep mode and the results are as follows.
First we have a test about the time to enter sleep. We set a GPIO(GPIO18 in this case) from high to low level before we call esp_light_sleep_start to start the light-sleep mode. As shown below, after about 200us, the chip completely goes to Light-sleep.
gpio_set_level(GPIO_NUM_18, 1);
vTaskDelay(2000 / portTICK_PERIOD_MS);
gpio_set_level(GPIO_NUM_18, 0);
esp_light_sleep_start();
Second test is the time to resume from light_sleep. After chip was waked up, the program is executed from where it was last stopped, rather than restart. So We configure ext0 as wake up source, and about 566us after ext0 source triggered, the chip resumed operation and GPIO18 output low. Figure shows this process.
esp_sleep_enable_ext0_wakeup(GPIO_NUM_34, 0);
gpio_set_level(GPIO_NUM_18, 0);
esp_light_sleep_start();
gpio_set_level(GPIO_NUM_18, 1);
Finally, the current during sleep was tested. We can wake the chip up from Light-sleep by different means, such as ext0, ext1 and timer. Different ways to take, the current consumption during Light-sleep will be different. the results are as follows.
| Wake source | current consumption during sleep |
|---|---|
| ext0 | 1.15mA |
| ext1 | 1.14mA |
| timer | 0.79mA |
Before enter Light-sleep, Those GPIO who powered by VDD3P3_CPU should be all disabled. otherwise, the current will be higher(about 1.5mA) due to GPIO leakage current.