When something goes wrong, particularly in the middle of a long print, it can be useful to have a log of what happened (at least as much as the electronics know). Logging of errors and other important events is an optional feature of RepRapFirmware 1.20 and later. Use the M929 to enable and disable logging and to specify the log file name. By default, logging is disabled. You can use a M929 command in config.g to enable it.
Some other way of obtaining diagnostics information are:
- There is a built-in setting in the web interface to request that the Duet log every G-code and its response, but during a print this can be overwhelming. You can obtain a little more information by having your slicer embed additional G-code into the print;, for example adding M114 (report position) to the code at every layer change.
- The firmware can be put in debugging mode with M111, which should result in many more messages. You can specify debugging messages only from certain submodules; to get a list, send M111 S1 P15. Debug output goes only to USB.
- It's not a log, but the M122 command will have the firmware report its status, including (for example) information about under- and over-voltage events. The output goes into the G-code console.