Hey guys! Today, we're diving into the nitty-gritty of setting serial port parameters in Ubuntu. Whether you're a hobbyist tinkering with embedded systems, a developer working on serial communication, or just a curious Linux user, understanding how to configure your serial ports is super important. Let’s get started and make sure you know your stuff when it comes to Ubuntu serial ports.

Understanding Serial Ports

Before we jump into the how-to, let's quickly cover what serial ports are and why you might need to tweak their settings. Serial communication involves transmitting data one bit at a time over a single wire (or channel). It's a simple but effective way for devices to talk to each other, especially over short distances. Common uses include connecting to microcontrollers, GPS modules, older printers, and various industrial equipment. The serial port parameters dictate how this communication happens.

Key Serial Port Parameters

• Baud Rate: This is the speed at which data is transmitted, measured in bits per second (bps). Both devices need to use the same baud rate to communicate effectively. Common baud rates include 9600, 19200, 38400, 57600, and 115200.
• Data Bits: This specifies the number of bits used to represent each character of data. Typically, this is 7 or 8 bits.
• Parity: This is a simple form of error checking. It can be set to Even, Odd, or None. When parity is enabled, an extra bit is added to each character to ensure the total number of 1s is either even (for Even parity) or odd (for Odd parity).
• Stop Bits: These are added to the end of each character to signal the end of the transmission. Usually, this is 1 or 2 bits.
• Flow Control: This manages the flow of data to prevent one device from overwhelming the other. Common options are None, XON/XOFF (software flow control), and RTS/CTS (hardware flow control).

Identifying Your Serial Port

First things first, you need to know which serial port you're working with. In Ubuntu, serial ports are typically represented as device files in the /dev directory. Common names include ttyS0, ttyS1 (for physical serial ports), and ttyUSB0, ttyUSB1 (for USB serial adapters).

How to List Serial Ports

To find out which serial ports are available on your system, you can use the following command in the terminal:

dmesg | grep tty

This command will display kernel messages related to TTY devices, which often include the names of your serial ports. Alternatively, you can use:

ls /dev/tty*

This lists all TTY devices in the /dev directory, making it easy to spot your serial ports. Once you've identified the correct port (e.g., /dev/ttyUSB0), you can proceed to configure it.

Setting Serial Port Parameters Using stty

The stty command is your go-to tool for configuring serial port settings in Linux. It's a command-line utility that allows you to view and modify various terminal settings, including baud rate, parity, and flow control.

Basic Syntax

The basic syntax for using stty to set serial port parameters is:

stty -F <serial_port> <parameter1> <value1> <parameter2> <value2> ...

• -F <serial_port>: Specifies the serial port you want to configure (e.g., -F /dev/ttyUSB0).
• <parameter>: The setting you want to change (e.g., speed, parenb, parodd).
• <value>: The value you want to assign to the parameter (e.g., 9600, even, none).

Example Configurations

Let's look at some practical examples to illustrate how to use stty.

Setting Baud Rate

To set the baud rate to 9600 for /dev/ttyUSB0, use the following command:

stty -F /dev/ttyUSB0 9600

To set it to 115200, you'd use:

stty -F /dev/ttyUSB0 115200

Setting Parity

To enable even parity:

stty -F /dev/ttyUSB0 parenb parodd cs7

Here, parenb enables parity, parodd enables odd parity (use -parodd for even parity), and cs7 sets the character size to 7 bits (required when using parity).

To disable parity:

stty -F /dev/ttyUSB0 -parenb cs8

Here, -parenb disables parity, and cs8 sets the character size to 8 bits.

Setting Stop Bits

stty doesn't directly control the number of stop bits. However, most systems default to 1 stop bit, which is usually sufficient. If you need 2 stop bits, you might need to configure this in your application or use a more advanced serial port configuration tool.

Setting Flow Control

To enable hardware flow control (RTS/CTS):

stty -F /dev/ttyUSB0 crtscts

To disable hardware flow control:

stty -F /dev/ttyUSB0 -crtscts

To enable software flow control (XON/XOFF):

stty -F /dev/ttyUSB0 ixon ixoff

To disable software flow control:

stty -F /dev/ttyUSB0 -ixon -ixoff

Combining Parameters

You can combine multiple parameters in a single stty command. For example, to set the baud rate to 115200, enable even parity, and enable hardware flow control:

stty -F /dev/ttyUSB0 115200 parenb parodd cs7 crtscts

Viewing Current Settings

To view the current settings for a serial port, simply use stty with the -F option:

stty -F /dev/ttyUSB0 -a

The -a option displays all current settings in a human-readable format. This is super handy for verifying that your changes have been applied correctly.

Using setserial for Advanced Configuration

For more advanced configuration options, especially for legacy serial ports (ttyS*), you can use the setserial command. This tool allows you to configure IRQ settings, UART type, and other low-level parameters.

Installing setserial

If setserial is not already installed on your system, you can install it using apt:

sudo apt update
sudo apt install setserial

Basic Syntax

The basic syntax for using setserial is:

sudo setserial <serial_port> <options>

Example Configurations

Viewing Serial Port Information

To view detailed information about a serial port, use the -g option:

sudo setserial -g /dev/ttyS0

Setting the UART Type

You can set the UART type using the uart option. For example, to set the UART type to 16550A:

sudo setserial /dev/ttyS0 uart 16550A

Setting the IRQ

Setting the IRQ (Interrupt Request) is crucial for proper serial port operation, especially for older hardware. You can set the IRQ using the irq option. For example, to set the IRQ to 4:

sudo setserial /dev/ttyS0 irq 4

Note: Be cautious when modifying IRQ settings, as incorrect settings can cause conflicts and system instability. Always refer to your hardware documentation for the correct IRQ value.

Persisting Changes

Changes made with setserial are not persistent across reboots by default. To make the changes permanent, you need to modify the /etc/serial.conf file. Add the necessary setserial commands to this file, so they are executed at boot time.

Example /etc/serial.conf Entry

/dev/ttyS0 uart 16550A irq 4

After modifying /etc/serial.conf, you can apply the changes by running:

sudo setserial /dev/ttyS0 autoconfig

Using Minicom for Serial Communication

Once you've configured your serial port, you'll likely want to use it to communicate with a device. Minicom is a popular terminal program for serial communication in Linux.

Installing Minicom

If Minicom is not already installed, you can install it using apt:

sudo apt update
sudo apt install minicom

Configuring Minicom

To configure Minicom, run it with the -s option:

sudo minicom -s

This will open the Minicom setup menu. Here, you can configure various settings, including:

• Serial port: Set the serial device (e.g., /dev/ttyUSB0).
• Baud rate: Set the baud rate (e.g., 9600, 115200).
• Data bits, Parity, Stop bits: Configure these settings as needed.
• Hardware Flow Control: Enable or disable hardware flow control.
• Software Flow Control: Enable or disable software flow control.

Navigate the menu using the arrow keys, and press Enter to select an option. Once you've configured the settings, select "Save setup as dfl" to save the settings as the default configuration. Then, exit the setup menu.

Running Minicom

To run Minicom with the default configuration, simply type:

minicom

This will open the Minicom terminal, allowing you to send and receive data through the serial port. Type Ctrl+A followed by Q to exit Minicom.

Troubleshooting Serial Port Issues

Sometimes, things don't go as planned. Here are some common issues and how to troubleshoot them:

No Data Received

• Check the serial port: Make sure you're using the correct serial port (e.g., /dev/ttyUSB0).
• Verify the baud rate: Ensure that the baud rate matches the device you're communicating with.
• Check the wiring: Ensure that the serial cable is properly connected and that the wiring is correct.
• Verify parity and stop bits: Ensure that these settings match the device's requirements.

Garbled Data

• Baud rate mismatch: This is the most common cause of garbled data. Double-check that the baud rates match on both devices.
• Parity mismatch: Ensure that the parity settings are the same on both devices.
• Data bits mismatch: Ensure that the data bits settings are the same on both devices.

Permission Issues

• User permissions: Ensure that your user account has permission to access the serial port. You may need to add your user to the dialout group:

  sudo usermod -a -G dialout $USER
  newgrp dialout
  

Hardware Issues

• Faulty cable: Try using a different serial cable to rule out a hardware issue.
• Defective serial port: If possible, try using a different serial port to see if the issue persists.

Conclusion

So, there you have it! Configuring serial ports in Ubuntu might seem daunting at first, but with the right tools and a bit of practice, you'll be a pro in no time. Remember to double-check your settings, verify your connections, and don't be afraid to dive into the documentation. Happy tinkering, and may your serial communication be smooth and error-free!

By mastering the stty and setserial commands, along with tools like Minicom, you can effectively manage serial communication for a wide range of applications. Whether you're debugging embedded systems, configuring IoT devices, or simply connecting to legacy hardware, these skills are invaluable for any Linux enthusiast or developer. Keep experimenting, and you'll become more comfortable with the intricacies of serial communication in Ubuntu. Good luck, and have fun!