The CH340 driver in the Linux kernel-based system such as Raspberry Pi is too old. It has compatibility issues with the new CH340G chip. You need to install the new driver manually.
The Linux driver source code download url is here:
Raspberry Pi 4B, Broadcom BCM711, 4GB Ram, install the official Raspberry Pi system released on May 7th 2021. The kernel version is 5.10.
Input the command to find the serial device driver installed in the system.
Find ch341.ko and delete.
sudo rm /lib/modules/(version)/kernel/drivers/usb/serial/ch341.ko
Download the CH340 driver source code and unzip it.
Enter the source directory and compile.
cd CH341SER_LINUX && make
If the kernel header file is not installed in the system, the compiler will prompt an error, /lib/modules/(version)/build not found.
Install Raspberry Pi kernel header files.
sudo apt install raspberrypi-kernel-headers
Recompile after installing the kernel header files. If the compiler prompts an unknown error of type'wait-queue+t', please use vi to open the ch34x.c file, find and comment out line 591.
After successful compilation, the ch34x.ko file will be generated.
Copy the ch34x.ko file to the kernel driver directory, and install the driver.
sudo cp ch34x.ko /lib/modules/(version)/kernel/drivers/usb/serial/ sudo depmod
Connect the 3D printer with a USB cable and turn on the power. If the driver is successfully installed, the ttyUSB0 device will appear in the /dev/ directory.
Find the ttyUSB0 device in OctoPrint and set the baud rate to 115200.
Open the port and switch to the Terminal panel. The firmware version information of the 3D printer is displayed in the console, and the connection is successful.