How to Read Data from Serial Port in a Linux Environment

A comprehensive guide to reading data from a serial port in Linux, addressing common errors and solutions for embedded systems. --- This video is based on the question https://stackoverflow.com/q/66094058/ asked by the user 'Creatorczyk' ( https://stackoverflow.com/u/14818512/ ) and on the answer https://stackoverflow.com/a/66094157/ provided by the user 'Antti Haapala -- Слава Україні' ( https://stackoverflow.com/u/918959/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions. Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: How read data from serialport? Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/licensing The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/by-sa/4.0/ ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/by-sa/4.0/ ) license. If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com. --- How to Read Data from Serial Port in a Linux Environment Working with serial ports can be a bit tricky, especially when handling data input and output. Many developers encounter challenges when trying to read data sent from another device. If you've ever received an error message like "Resource temporarily unavailable" while attempting to read from a serial port on Linux, this guide is for you. We're here to help you understand the problem and present effective solutions. Understanding the Issue In our scenario, a simple program has been written to send data from a serial port. While the message is successfully sent to another device, the attempt to read data back results in an error. This is a common issue when the serial port is set to non-blocking mode, leading to the inability to read data when none is available. The Error Message The relevant error message is: [[See Video to Reveal this Text or Code Snippet]] This error typically arises from two potential sources: Non-blocking Mode: The port is opened in non-blocking mode, which means that the read operation will not wait for data to become available before returning. Data Availability: There may simply not be any data available at that instant for reading. Solution: How to Fix the Error To address the reading issue effectively, we have two primary methods to resolve the problem. Let’s detail both options: Option 1: Modify the Port Opening Flags The straightforward fix involves changing the way the serial port is opened in your code. By removing the O_NDELAY flag, you switch from non-blocking mode to blocking mode, allowing the read operation to wait until data is available. Here’s what your modified code line would look like: [[See Video to Reveal this Text or Code Snippet]] Option 2: Use poll() or select() Functions If you wish to keep the non-blocking mode, you can employ poll() or select() to wait for the descriptor to be ready for reading. This method is slightly more complex but allows for better control over multiple file descriptors. Using poll() Example of using poll(): [[See Video to Reveal this Text or Code Snippet]] Conclusion When dealing with serial ports in Linux, understanding the implications of blocking vs. non-blocking modes is crucial. By either removing O_NDELAY or implementing a waiting mechanism like poll() or select(), you can effectively read data from the serial port without running into resource availability issues. Final Tips Always ensure that your serial settings are properly configured before reading data. Debugging serial communication can be tricky; make sure to check connections and device compatibility. With these adjustments, you should be better equipped to handle data reading from serial ports in your applications. Happy coding!