vscode arduino [Warning] Output path is not specified. Unable to reuse previously compiled files. Upload could be slow. See README.

The warning message "Output path is not specified. Unable to reuse previously compiled files. Upload could be slow. See README." typically occurs when using the Visual Studio Code (VS Code) Arduino extension. This warning indicates that the Arduino extension is unable to find the previously compiled files, which can result in slower upload times.

To address this warning, you need to specify the output path for the compiled files in your Arduino project. By specifying the output path, the Arduino extension will be able to locate and reuse the previously compiled files, leading to faster upload times.

To specify the output path in VS Code Arduino, you can follow these steps:

  1. Open the platformio.ini file in your Arduino project.
  2. Look for the [env:...] section that corresponds to your target board configuration.
  3. Add the following line under the [env:...] section:

ini build.build_flags = -Wl,-Map,output.map -Wl,--gc-sections -Wl,-s -Wl,--defsym=__rtc_localtime=0

  1. Save the platformio.ini file.

By adding the build.build_flags line to the platformio.ini file, you are specifying additional build flags that include the output path information. This allows the Arduino extension to locate and reuse the previously compiled files, resulting in faster upload times.

After making these changes, you should no longer see the warning message about the output path not being specified. Instead, the Arduino extension will be able to reuse the previously compiled files, leading to improved upload performance.

Remember to consult the README file of the Arduino extension or the official documentation for further information and troubleshooting steps related to this warning message.