USB Serial/JTAG Controller Console

On chips with an integrated USB Serial/JTAG Controller, it is possible to use the part of this controller that implements a serial port (CDC) to implement the serial console, instead of using UART with an external USB-UART bridge chip. ESP32-C3 contains this controller, providing the following functions:

  • Bidirectional serial console, which can be used with IDF Monitor or another serial monitor.

  • Flashing using esptool.py and idf.py flash.

  • JTAG debugging using e.g. OpenOCD, simultaneous with serial operations.

Note that, in contrast with the USB OTG peripheral in some Espressif chips, the USB Serial/JTAG Controller is a fixed function device, implemented entirely in hardware. This means it cannot be reconfigured to perform any function other than to provide a serial channel and JTAG debugging functionality.

Hardware Requirements

Connect ESP32-C3 to the USB port as follows:

GPIO

USB

19

D+ (green)

18

D- (white)

GND

GND (black)

+5V (red)

Some development boards may offer a USB connector for the USB Serial/JTAG Controller — in that case, no extra connections are required.

Software Configuration

USB console feature can be enabled using CONFIG_ESP_CONSOLE_USB_SERIAL_JTAG option in menuconfig tool (see CONFIG_ESP_CONSOLE_UART).

Once the option is enabled, build the project as usual.

Alternatively, you can access the output through usb_serial_jtag port but make sure the option CONFIG_ESP_CONSOLE_SECONDARY_USB_SERIAL_JTAG in choice ESP_CONSOLE_SECONDARY is selected.

警告

Besides output, if you also want to input or use REPL with console, please select CONFIG_ESP_CONSOLE_USB_SERIAL_JTAG.

Uploading the Application

The USB Serial/JTAG Controller is able to put the ESP32-C3 into download mode automatically. Simply flash as usual, but specify the USB Serial/JTAG Controller port on your system: idf.py flash -p PORT where PORT is the name of the proper port.

Limitations

There are several limitations to the USB console feature. These may or may not be significant, depending on the type of application being developed, and the development workflow.

  1. If the application accidentally reconfigures the USB peripheral pins, or disables the USB Serial/JTAG Controller, the device will disappear from the system. After fixing the issue in the application, you will need to manually put the ESP32-C3 into download mode by pulling low GPIO9 and resetting the chip.

  2. If the application enters deep sleep mode, USB CDC device will disappear from the system.

  3. The behavior between an actual USB-to-serial bridge chip and the USB Serial/JTAG Controller is slightly different if the ESP-IDF application does not listen for incoming bytes. An USB-to-serial bridge chip will just send the bytes to a (not listening) chip, while the USB Serial/JTAG Controller will block until the application reads the bytes. This can lead to a non-responsive looking terminal program.

  4. The USB CDC device won’t work in sleep modes as normal due to the lack of APB clock in sleep modes. This includes deep-sleep, light-sleep (automataic light-sleep as well).

  5. The power consumption in sleep modes will be higher if the USB CDC device is in use.

    This is because we want to keep the USB CDC device alive during software reset by default.

    However there is an issue that this might also increase the power consumption in sleep modes. This is because the software keeps a clock source on during the reset to keep the USB CDC device alive. As a side-effect, the clock is also kept on during sleep modes. There is one exception: the clock will only be kept on when your USB CDC port is really in use (like data transaction), therefore, if your USB CDC is connected to power bank or battery, etc., instead of a valid USB host (for example, a PC), the power consumption will not increase.

    If you still want to keep low power consumption in sleep modes:

    1. If you are not using the USB CDC port, you don’t need to do anything. Software will detect if the CDC device is connected to a valid host before going to sleep, and keep the clocks only when the host is connected. Otherwise the clocks will be turned off as normal.

    2. If you are using the USB CDC port, please disable the menuconfig option CONFIG_RTC_CLOCK_BBPLL_POWER_ON_WITH_USB. The clock will be switched off as normal during software reset and in sleep modes. In these cases, the USB CDC device may be unplugged from the host.

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