Serial communication is a very common operation in Linux systems, especially in embedded systems, industrial equipment, and other scenarios where serial communication is required. In order to ensure the normal operation of the serial port equipment, it is very important to check the connection status and configuration information of the serial port. This article will introduce how to check the connection status of the serial port on Linux to help you effectively diagnose serial port communication problems.
1. Use the stty command to view the serial port configuration
The stty command is a tool in Linux for setting and querying terminal (serial port device) configuration. Through it, we can check and modify various parameters of the serial port, including baud rate, data bits, flow control, and whether the DCD (Data Carrier Detect) signal is enabled.
Check the serial port configuration:
Use the following command to view the detailed configuration of the serial port device:
stty -F /dev/ttyUSB0 -a
Among them, /dev/ttyUSB0 is the path of the serial port device, which can be modified to the corresponding device (such as /dev/ttyS0) according to actual conditions. This command will display all configuration parameters of the serial port, including baud rate, data bit, stop bit and other information.
Check DCD signal:
Check whether there are DCD-related parameters in the output via stty -F /dev/ttyUSB0 -a. If -clocal is disabled (indicating that the DCD signal is not ignored), the DCD signal should be high when the peer device is connected. If there is no device connection, the DCD signal will usually be low.
2. Use /proc/tty/driver/serial to view the status of the serial port device
Linux's /proc file system provides kernel and system status information. By reading the /proc/tty/driver/serial file, you can obtain the status information of the serial port device in the system, especially information related to hardware signals (such as DCD).
View serial port information:
cat /proc/tty/driver/serial
Output example:
serinfo:1.0 driver revision:
0: uart:16550A mmio:0xFF180000 irq:38 tx:0 rx:0 RTS|CTS|DTR|DSR|CD
explain:
- uart:16550A: means that the serial port uses a 16550A UART chip.
- mmio:0xFF180000: Memory mapped address, used to access the serial port hardware.
- irq:38: Interrupt number, used to signal the CPU with hardware interrupt.
- RTS|CTS|DTR|DSR|CD: These are the hardware control signals of the serial port. CD indicates Carrier Detect, that is, whether the peer device is connected.
If you see a CD signal, the device is connected. If there is no CD signal, there is no device connection.
3. Use the dmesg command to view the serial device log
In Linux, the dmesg command is used to view the system's kernel logs. When the serial port device is connected or disconnected, the kernel will record relevant event information. Through the dmesg command, you can view the connection status of the serial port device.
Check the connection status of the serial port device:
dmesg | grep ttyUSB0
This displays the relevant logs for the /dev/ttyUSB0 serial device. Usually, if the serial port device is connected successfully, the system will display a log similar to the following:
[ 1234.567890] usb 1-1.2: pl2303 converter now attached to ttyUSB0
If the device is disconnected, the log displays a similar disconnect message.
4. Use getty or other serial port tools
If you need to further verify whether the serial port can work properly, you can use getty and other tools to initialize the serial port connection.
Use getty to start the serial port terminal:
sudo getty -L ttyUSB0 9600 vt100
If the serial port device is not connected, getty may not be initialized successfully and will not display the normal terminal output. This is a simple and effective way to detect whether the serial port device is working properly.
5. Check DCD signal status
To ensure that the peer device is connected, usually in Linux, the serial device will have a Carrier Detect (DCD) signal. This signal will go high when the device is connected, indicating that the signal link has been established. By disabling the clocal configuration, the detection of DCD signals can be enabled.
Disable clocal:
stty -F /dev/ttyUSB0 -clocal
After disabling clocal, the serial device will wait for the DCD signal, which can accurately determine whether there is a connection between the peer device. If the DCD signal is low, it means there is no device connection.
Summarize
Serial devices are very common in Linux systems, and checking their connection status is a key step to ensure that the device works properly. Through the stty command, we can fully understand the connection status of the serial port device through the stty command, read /proc/tty/driver/serial to obtain the hardware signal status, use dmesg to view the device log, and use getty to perform serial port testing.
The DCD signal is the key signal to determine whether the device is connected. After clocal is disabled, the system will monitor the changes in the DCD signal.
Using the /proc/tty/driver/serial and dmesg logs, you can quickly view the hardware status of the serial port device.
Combined with tools such as getty, you can further verify whether the serial port is working normally.
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