Chapter 4. API Guides
4.5.5 CRC Check For Wake Stubs
During deep sleep, all RTC Fast memory areas will be validated with CRC. When ESP32-S2 wakes up from deep
sleep, the RTC fast memory will be validated with CRC again. If the validation passes, the wake stubs code will be
executed. Otherwise, the normal initialization, bootloader and esp-idf codes will be executed.
Note: When the CONFIG_ESP_SYSTEM_ALLOW_RTC_FAST_MEM_AS_HEAP option is enabled, all the RTC fast
memory except the wake stubs area is added to the heap.
4.6 Device Firmware Upgrade through USB
Device Firmware Upgrade (DFU) is a mechanism for upgrading the firmware of devices through Universal Serial
Bus (USB). DFU is supported by ESP32-S2 chips. The necessary connections for the USB peripheral are shown in
the following table.
GPIO USB
20 D+ (green)
19 D- (white)
GND GND (black)
+5V +5V (red)
Note: The ESP32-S2 chip needs to be in bootloader mode for the detection as a DFU device and flashing. This
can be achieved by pulling GPIO0 down (e.g. pressing the BOOT button), pulsing RESET down for a moment and
releasing GPIO0.
Warning: Some cables are wired up with non-standard colors and some drivers are able to work with swapped
D+ and D- connections. Please try to swap the cables connecting to D+ and D- if your device is not detected.
The software requirements of DFU are included in Step 1. Install prerequisites of the Getting Started Guide.
Section Building the DFU Image describes how to build firmware for DFU with ESP-IDF and Section Flashing the
Chip with the DFU Image deals with flashing the firmware.
4.6.1 Building the DFU Image
The DFU image can be created by running:
idf.py dfu
which creates dfu.bin in the build directory.
Note: Don’t forget to set the target chip by idf.py set-target before running idf.py dfu. Otherwise,
you might create an image for a different chip or receive an error message something like unknown target
'dfu'.
4.6.2 Flashing the Chip with the DFU Image
The DFU image is downloaded into the chip by running:
Espressif Systems 1301
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