https://github.com/espressif/arduino-esp32/issues/544

ESP32 DEVKIT1

schematic: SchematicsforESP32.pdf

to get into bootloader mode (out of box) plug module in (red led will show that it has power from usb) and:

press EN - press BOOT - release EN - release BOOT

dpavlin@x200:/mnt/nuc/esptool$ ./esptool.py -p /dev/ttyUSB0 --chip esp32 read_mac
esptool.py v2.7-dev
Serial port /dev/ttyUSB0
Connecting........_
Chip is ESP32D0WDQ6 (revision 1)
Features: WiFi, BT, Dual Core, 240MHz, VRef calibration in efuse, Coding Scheme None
MAC: 3c:71:bf:aa:fc:24
Uploading stub...
Running stub...
Stub running...
MAC: 3c:71:bf:aa:fc:24
Hard resetting via RTS pin...

dpavlin@x200:/mnt/nuc/esptool$ ./esptool.py -p /dev/ttyUSB0 --chip esp32 chip_id
esptool.py v2.7-dev
Serial port /dev/ttyUSB0
Connecting........__
Chip is ESP32D0WDQ6 (revision 1)
Features: WiFi, BT, Dual Core, 240MHz, VRef calibration in efuse, Coding Scheme None
MAC: 3c:71:bf:aa:fc:24
Uploading stub...
Running stub...
Stub running...
Warning: ESP32 has no Chip ID. Reading MAC instead.
MAC: 3c:71:bf:aa:fc:24
Hard resetting via RTS pin...

dpavlin@x200:/mnt/nuc/esptool$ ./esptool.py -p /dev/ttyUSB0 --chip esp32 flash_id
esptool.py v2.7-dev
Serial port /dev/ttyUSB0
Connecting........_____....._____....._____....._____.
Chip is ESP32D0WDQ6 (revision 1)
Features: WiFi, BT, Dual Core, 240MHz, VRef calibration in efuse, Coding Scheme None
MAC: 3c:71:bf:aa:fc:24
Uploading stub...
Running stub...
Stub running...
Manufacturer: 20
Device: 4016
Detected flash size: 4MB
Hard resetting via RTS pin...