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This sample program shows how to bridge between ESP32(UART) and your PC(USB).
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docs Update ESP32 firmware (Fix TRNG) Sep 6, 2019 Update ESP32 firmware Aug 21, 2019
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mbed-os.lib Updated to mbed-os 5.9.1 Jun 20, 2018


Please see here for Japanese version.

This sample program shows how to bridge between ESP32(UART) and your PC(USB).
You can utilize this sample program for Flash writing or ESP32 evaluation.
GR-LYCHEE is equipped with ESP32 on the board.
GR-PEACH can add ESP 32 by connecting GR-WIRELESS CAMERA Shield.

How to use

The following two items are stored in docs\

  • GR-LYCHEE_ESP32_Serial_Bridge.bin (for GR-LYCHEE)
  • GR-PEACH_ESP32_Serial_Bridge.bin (for GR-PEACH)
  • ESP32_firmware (ESP32 F/W update data by AT command)

If you use the sample code as is, please unzip the file and copy GR-xxxxx_ESP32_Serial_Bridge.bin to your borad.

Serial setting

When you use GR-LYCHEE_ESP32_Serial_Bridge, you need to connect your PC and MicroUSB Connector(RZ/A1 Ch.0).

If your PC isn't Windows10, you need to install the specified driver from the below URL.

Unfortunately, since that is "Unsigned driver", you cannot install as is depending on your Windows version. Since the setting method is different for each PC, please search with "Unsigned driver" keyword on the search site.

If you want to confirm the serial communication the terminal software on your PC, please specify the below values.

Baud rate 115200
Data 8bit
Parity none
Stop 1bit
Flow control none


Pressing USER_BUTTON0 resets ESP32.

Change to the Flash writing mode

You can change ESP32 to the Flash writing mode by holding down USER_BUTTON0 and connecting the USB cable. LED1 on the board lights during the write mode. In the flash writing mode, the LED1 lights up. To cancel the flash writing mode, please reconnect the USB cable again.

How to update ESP32 firmware

Write the following firmware in the docs/ESP32_firmware to your board:

  • GR-LYCHEE_ESP32_Serial_Bridge.bin (for GR-LYCHEE)
  • GR-PEACH_ESP32_Serial_Bridge.bin (for GR-PEACH)

Espressif’s official Flash Download Tools:

The settings are as follows. If the COM port is already open in the terminal software, please close the terminal software.

  • SPI SPEED : 40MHz
  • FLASH SIZE : 32Mbit
  • COM : Set your board COM.
  • BAUD : 460800 (If a write error occurs, try again with the smaller value.)

The update file is in the docs\

Path offset
0x1000_bootloader.bin 0x1000
0x20000_at_customize.bin 0x20000
0x21000_ble_data.bin 0x21000
0x24000_server_cert.bin 0x24000
0x26000_server_key.bin 0x26000
0x28000_server_ca.bin 0x28000
0x2a000_client_cert.bin 0x2a000
0x2c000_client_key.bin 0x2c000
0x2e000_client_ca.bin 0x2e000
0x30000_factory_param_lychee_and_peach.bin 0x30000
0xf000_phy_init_data.bin 0xf000
0x100000_esp-at.bin 0x100000
0x8000_partitions_at.bin 0x8000


  1. While holding down USER_BUTTON0, connect the PC with MicroUSB connector Ch.0 using a USB cable.
  2. Press the Erase button on the tool to erase the unwanted data on the flash. The green area labeled IDLE in the tool changes to FINISH when finished.
  3. Disconnect the USB cable and connect the USB cable while pressing USER_BUTTON0 again.
  4. Press the START button on the tool to start writing. The green area labeled IDLE in the tool changes to FINISH when finished.
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