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James John
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Filament Explorer
Asked: 2023-06-17T12:30:04+00:00 In:

How can I print debug information to the terminal in Marlin?

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I would like to know how to print debug information to the terminal in Marlin. Specifically, I’m searching for an alternative to System.out.println() or Console.WriteLine() that utilizes M118.

For instance, I want to send a message to the OctoPrint terminal every time a specific variable changes its value, simulating the behavior of M118.

To achieve this, I plan to hardcode these commands into the firmware files before compiling/flashing.

However, I’m uncertain about how to adapt M118.cpp, which is primarily intended for parsing user-provided strings, for this purpose.

I would appreciate any assistance or guidance on this matter.

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    1 Answer

    1. Mohamed Elgendy
      Best Answer
      Print Jedi Additive manufacturing Engineer

      If you’re using Marlin firmware and want to print debug messages to the terminal, you can achieve this by using the M118 command. M118 is the equivalent of System.out.println() or Console.WriteLine() in other programming languages.

      Here’s what you can do:

      1. Open the Marlin firmware files in a text editor of your choice.
      2. Look for the “Configuration_adv.h” file, which contains advanced configuration options.
      3. In this file, find the section that defines the SERIAL_MOTOR_DEBUG option. By default, it is usually commented out with // at the beginning of the line. Remove the // to uncomment and enable serial debugging.
      4. Save the changes to the “Configuration_adv.h” file.
      5. Now, you can use the M118 command to send debug messages to the terminal. The syntax for M118 is as follows:

      M118 P<message>

      Replace <message> with the debug message you want to display. For example:

      M118 P”Variable X changed its value!”
      1. In your firmware code, identify the appropriate location where you want to add the debug message. This could be within a conditional statement or whenever the specific variable changes its value.
      2. Insert the M118 command with the desired debug message at the relevant location in your code. Here’s an example:
        if (variableX != previousValueX) {
        M118 P"Variable X changed its value!";
        previousValueX = variableX;
        }
      3. Save the changes to the firmware files.
      4. Recompile and flash the modified firmware to your printer.

      Once the modified firmware is flashed and running, the debug messages specified by M118 commands will be sent to the OctoPrint terminal or any connected terminal software.

      Note that M118.cpp is primarily designed to parse strings given by the user, but you can adapt it for your debugging purposes by embedding the M118 commands directly in the firmware files.

      I hope this explanation helps! Feel free to ask if you have any further questions.