USB-OTG Peripheral Introduction

[中文]

The ESP32-S2/S3 and other chips come with built-in USB On-The-Go (USB-OTG) peripherals. They include a USB controller and USB PHY, supporting connection to a PC via a USB cable, enabling USB Host and USB Device functionalities.

USB-OTG Transfer Rate

For the ESP32-S2/S3, the USB On-The-Go (USB-OTG) Full Speed bus transfer rate is 12 Mbps. However, due to the presence of checksum and synchronization mechanisms in USB transfers, the actual effective transfer rate will be lower than 12 Mbps. The specific values depend on the transfer type and are outlined in the table below:

Transfer Types

Control

Interrupt

Bulk

Isochronous

Application Scenarios

Device Initialization and Management

Mouse and Keyboard

Printers and Bulk Storage

Streaming Audio and Video

Supports Low Speed

Yes

Yes

No

No

Checksum and Retransmission

Yes

Yes

Yes

No

Ensuring Transfer Speed

No

No

No

Yes

Utilizing Fixed Bandwidth

Yes (10%)

Yes (90%)

No

Yes (90%)

Reducing Latency Time

No

Yes

No

Yes

Maximum Transfer Size

64 Bytes

64 Bytes

64 Bytes

~512 Bytes

Number of Packets Transferred Per Millisecond

1

19

1

Theoretical Effective Rate

64000 Bytes/s

1216000 Bytes/s

512000 Bytes/s

  • Calculation Formula for Transfer Rate: Transfer Rate (Bytes/s) = Maximum Packet Size * Number of Packets Transferred Per Millisecond * 1000

  • Control transfers are used for transmitting device control information and involve multiple stages. The effective transfer rate needs to be calculated based on the implementation of the protocol stack.

USB-OTG Peripheral Built-in Features

Using USB OTG Console for Firmware Download and Logging

For chips like ESP32-S2/S3 with built-in USB On-The-Go (USB-OTG) peripherals, the ROM Code contains the functionality of USB Communication Device Class (CDC). This feature can be utilized as an alternative to UART interfaces, enabling functions such as logging, console access, and firmware downloads.

  1. Since the USB OTG Console is initially disabled, follow these steps to perform the first firmware download:

    1. Enable the USB OTG Console feature in menuconfig and then compile the firmware.

    2. Manually pull down the Boot pin of the chip and connect the chip to the PC via USB to enter download mode. The PC will detect a new serial port device, listed as COM* on Windows, /dev/ttyACM* on Linux, and /dev/cu* on MacOS.

    3. Use the esptool utility (or directly use idf.py flash) to configure the corresponding serial port and download the firmware.

  2. After the initial download, the USB OTG Console functionality will be automatically enabled. You can then connect to the PC via USB, and the PC will detect a new serial port device, listed as COM* on Windows, /dev/ttyACM* on Linux, and /dev/cu* on MacOS. Log data will be printed from this virtual serial port.

  3. Users no longer need to manually pull down the Boot control pin. To download firmware, use the esptool utility (or directly use idf.py flash) to configure the corresponding serial port. During the download, esptool will automatically reset the device and switch it to download mode using the USB control protocol.

For more detailed information, please refer to USB OTG Console

Download firmware using USB OTG DFU

For chips like ESP32-S2/S3 with built-in USB On-The-Go (USB-OTG) peripherals, the ROM Code contains the functionality of USB DFU (Device Firmware Upgrade). This feature enables the implementation of a standard DFU download mode.

  1. To download firmware using DFU, users need to manually enter download mode each time by pulling down the Boot control pin of the chip and connecting it to the PC via USB.

  2. Run the command idf.py dfu in the project directory to generate the DFU firmware, and then use idf.py dfu-flash to download the firmware.

  3. If there are multiple DFU devices, users can use idf.py dfu-list to view the DFU device list and then use idf.py dfu-flash --path <path> to specify the download port.

For more detailed information, please refer to Device Firmware Upgrade via USB.

USB Host development using USB-OTG peripherals

USB-OTG peripherals support USB Host functionality, allowing users to connect directly to external USB devices through the USB interface. Starting from ESP-IDF version 4.4, the USB Host Driver is supported. Users can refer to the ESP-IDF USB Host documentation to develop USB Class Drivers.

Additionally, Espressif officially supports USB Host drivers for HID, MSC, CDC, UVC, and other device classes. Users can utilize these drivers directly for application development.

For more details on the USB Host solution, please refer to USB Host Solution.

USB Device development using USB-OTG peripherals

USB-OTG peripherals support USB Device functionality, and Espressif has officially adapted the TinyUSB stack. Users can develop USB standard devices or custom devices based on the open-source TinyUSB, such as HID, MSC, CDC, ECM, UAC, and more.

For more details on the USB Device solution, please refer to USB Device Solution.

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