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‎LICENSE

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‎README.md

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# ESP USB Bridge
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3-
- The JTAG bridge requires openocd-esp32 version v0.10.0-esp32-20201125 or newer.
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- The serial bridge requires ESP-IDF v4.3 or later.
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The ESP USB Bridge is an [ESP-IDF](https://github.com/espressif/esp-idf) project utilizing an ESP32-S2 chip to create a
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bridge between a computer (PC) and a target microcontroller (MCU). It can serve as a replacement for USB-to-UART chips
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(e.g. CP210x).
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The concept of ESP USB Bridge is shown in the following figure.
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<img src="images/board.png" height="400" alt="board">
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ESP32-S2 creates a composite USB device accessible from the PC when they are connected through an USB cable. The main
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features are the following.
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- *Serial bridge*: The developer can run [esptool](https://github.com/espressif/esptool) or connect a terminal program
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to to the serial port provided by the USB composite device. The communication is transferred in both directions
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between the PC and the target MCU through the ESP32-S2-based bridge.
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- *JTAG brige*: [openocd-esp32](https://github.com/espressif/openocd-esp32) can be run on the PC which will connect to
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the custom USB device identified by the vendor and product identificators. The ESP32-S2 acts again as bridge
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between the PC and the MCU, and transfers the JTAG communication between them in both directions.
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- *Mass storage device*: An USB Mass storage disk is created which can be accessed by a file explorer in the PC.
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Binaries can be copied to this disk and the ESP32-S2 will use them to flash the target MCU.
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## How to Compile the Project
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[ESP-IDF](https://github.com/espressif/esp-idf) v4.3 or newer can be used to compile the project. Please read the
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documentation of ESP-IDF for setting up the environment.
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- `idf.py menuconfig` can be used to change the default configuration. The project-specific settings are in the
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"Bridge Configuration" sub-menu.
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- `idf.py build` will build the project binaries.
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- `idf.py -p PORT flash monitor` will flash the ESP32-S2 and open the terminal program for monitoring. Please note that
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PORT is the serial port created by an USB-to-UART chip connected to the serial interface of ESP32-S2 (not the direct
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USB interface provided by ESP32-S2). This serial connection has to be established only for flashing. The ESP USB
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Bridge can work through the USB interface after that.
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The initial flashing can be done by other means as well as it is pointed out in
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[this guide](https://docs.espressif.com/projects/esp-idf/en/latest/esp32s2/api-guides/usb-console.html#initial-upload).
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## Development Board
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A simple development board connecting an ESP32-S2 to an ESP32 serving as target MCU is shown in the
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[schematics](images/schematics.pdf). The default configurations of the project
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were tested with this setup.
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Similar boards can be manufactured and flashed with the ESP USB Bridge. The pin numbers, vendor and product
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identificators and other settings can be changed in `idf.py menuconfig`.
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Please note that every board should have its own vendor and product identificators. There is also a possibility to
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register a product identificator under the [Espressif vendor identificator](https://github.com/espressif/usb-pids).
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## Serial Bridge
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The USB stack of ESP USB Bridge creates a virtual serial port through which the serial port of the target MCU is
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accessible. For example, this port can be `/dev/ttyACMx` or `COMx` depending on the operating system and is different
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from the PORT used for flashing the ESP USB Bridge.
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For example, an ESP32 target MCU can be flashed and monitored with the following commands.
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```bash
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cd AN_ESP32_PROJECT
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idf.py build
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idf.py -p /dev/ttyACMx flash monitor
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```
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Please note that [esptool](https://github.com/espressif/esptool) or any terminal program can connect to the virtual
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serial port as well.
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## JTAG Bridge
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The ESP USB Bridge provides a JTAG device. The following command can be used to connect to an ESP32 target MCU.
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```bash
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idf.py openocd --openocd-commands "-f interface/jtag_esp_remote.cfg -f target/esp32.cfg"
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```
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[Openocd-esp32](https://github.com/espressif/openocd-esp32) version v0.10.0-esp32-20201125 or newer can be used as
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well to achieve the same:
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```bash
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openocd -f interface/jtag_esp_remote.cfg -f target/esp32.cfg
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```
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Please note that the ESP remote protocol has to be selected to communicate with the target MCU. `idf.py openocd`
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without additional arguments would establish connection with the ESP32-S2 (if the JTAG pins are connected through a
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USB-to-JTAG bridge to the PC).
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You might want to make your own copy of `jtag_esp_remote.cfg` with the appropriate product and vendor identificators
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of your custom hardware:
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```
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interface jtag_esp_remote
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jtag_esp_remote_protocol usb
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jtag_esp_remote_vid_pid 0x303a 0x1002
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```
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The JTAG interface might need some additional setup to work. Please consult the
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[documentation of ESP-IDF](https://docs.espressif.com/projects/esp-idf/en/latest/esp32/api-guides/jtag-debugging/configure-ft2232h-jtag.html)
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for achieving this.
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## Mass Storage Device
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A mass storage device will show up in the PC connected to the ESP USB bridge. This can be accessed as any other USB storage
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disk. Binaries built in [the UF2 format](https://github.com/microsoft/uf2) can be copied to this disk and the ESP32-S2
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will flash the target MCU accordingly.
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Binary `uf2.bin` will be generated and placed into the `AN_ESP32_PROJECT/build` directory by running the following
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commands.
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```bash
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cd AN_ESP32_PROJECT
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idf.py uf2
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```
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## License
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This project is licensed under the Apache License Version 2.0 by Espressif Systems (Shanghai) Co Ltd. The copy of the
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license can be found in the [LICENSE](LICENSE) file.

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‎images/schematics.pdf

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