Linux setserial Command with Practical Examples

Introduction

In this lab, we will explore the Linux setserial command and its practical applications. The lab aims to teach you how to identify serial port information, configure serial port settings, and troubleshoot issues related to serial communication on a Linux system. We will start by understanding the purpose of the setserial command, then move on to using it to retrieve detailed information about the serial ports on your system. Finally, we will demonstrate how to configure various serial port settings, such as baud rate and interrupt request (IRQ), using the setserial command.

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Understand the Purpose of setserial Command

In this step, we will explore the purpose of the setserial command in Linux. The setserial command is a powerful tool used to configure and manage serial port settings on a Linux system.

The setserial command allows you to:

• Identify the current configuration of serial ports
• Set various parameters for serial ports, such as baud rate, I/O address, and interrupt request (IRQ)
• Troubleshoot issues related to serial communication

To begin, let's use the setserial command to get information about the serial ports on your system.

sudo setserial -g /dev/ttyS*

Example output:

/dev/ttyS0 uart:16550A port:0x03f8 irq:4
/dev/ttyS1 uart:16550A port:0x02f8 irq:3

This command retrieves the current configuration of all serial ports (/dev/ttyS*) on the system. The output shows the UART type, I/O port address, and IRQ for each serial port.

Now, let's say you need to change the configuration of a serial port, such as setting the baud rate. You can use the setserial command to do this:

sudo setserial /dev/ttyS0 baud_base 115200 spd_cust

This command sets the baud rate of the /dev/ttyS0 serial port to 115200 bps and enables custom baud rate settings.

The setserial command provides a wide range of options to configure various aspects of serial ports, such as:

• spd_normal: Set the standard baud rates
• spd_cust: Enable custom baud rates
• spd_vhi: Set the baud rate to 57600 bps
• spd_hi: Set the baud rate to 38400 bps
• spd_shi: Set the baud rate to 115200 bps

You can explore the full list of options by running man setserial in the terminal.

Identify Serial Port Information Using setserial

In this step, we will learn how to use the setserial command to identify detailed information about the serial ports on your Linux system.

First, let's list all the serial ports available on the system:

sudo setserial -g /dev/ttyS*

Example output:

/dev/ttyS0 uart:16550A port:0x03f8 irq:4
/dev/ttyS1 uart:16550A port:0x02f8 irq:3

This command provides the following information for each serial port:

• uart: The UART (Universal Asynchronous Receiver-Transmitter) type, which indicates the serial port hardware.
• port: The I/O port address of the serial port.
• irq: The interrupt request (IRQ) number assigned to the serial port.

To get more detailed information about a specific serial port, you can use the setserial command with the port name as an argument:

sudo setserial /dev/ttyS0 -a

Example output:

/dev/ttyS0, Line 0:
        Baud_base: 115200, close_delay: 50, divisor: 0
        closing_wait: 3000, custom_divisor: 0, max_baud: 0
        port: 0x03f8, irq: 4
        flags: (0x10) UPF_SKIP_TEST
        spd_cust: 0, spd: (0x00)

This command provides additional details about the /dev/ttyS0 serial port, including the baud rate, close delay, divisor, closing wait, custom divisor, maximum baud rate, and various flags.

Understanding the serial port information is crucial when configuring or troubleshooting serial communication issues on your Linux system.

Configure Serial Port Settings with setserial

In this step, we will learn how to use the setserial command to configure various settings for the serial ports on your Linux system.

Let's start by identifying the serial ports on your system:

sudo setserial -g /dev/ttyS*

Example output:

/dev/ttyS0 uart:16550A port:0x03f8 irq:4
/dev/ttyS1 uart:16550A port:0x02f8 irq:3

Now, let's say you want to change the baud rate of the /dev/ttyS0 serial port to 115200 bps and enable custom baud rate settings:

sudo setserial /dev/ttyS0 baud_base 115200 spd_cust

To verify the changes, you can run the setserial command again with the -a option:

sudo setserial /dev/ttyS0 -a

Example output:

/dev/ttyS0, Line 0:
        Baud_base: 115200, close_delay: 50, divisor: 0
        closing_wait: 3000, custom_divisor: 0, max_baud: 0
        port: 0x03f8, irq: 4
        flags: (0x10) UPF_SKIP_TEST
        spd_cust: 1, spd: (0x00)

The output shows that the baud rate is now set to 115200 bps, and the spd_cust flag is enabled, allowing you to use custom baud rates.

You can also use the setserial command to configure other serial port settings, such as:

• spd_normal: Set the standard baud rates
• spd_vhi: Set the baud rate to 57600 bps
• spd_hi: Set the baud rate to 38400 bps
• spd_shi: Set the baud rate to 115200 bps
• uart: Set the UART type (e.g., uart:16550A)
• port: Set the I/O port address
• irq: Set the interrupt request (IRQ) number

Remember to refer to the man setserial page for a complete list of available options and their descriptions.

Summary

In this lab, we learned about the purpose and usage of the setserial command in Linux. We started by understanding how the setserial command can be used to identify the current configuration of serial ports, including the UART type, I/O port address, and IRQ. We then explored how to use the setserial command to configure various settings for serial ports, such as baud rate and custom baud rates. Finally, we learned how to use the setserial command to obtain detailed information about the serial ports on the system, including their device names, UART types, and other relevant details.

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