On the Original Prusa XL, communication with the peripheral boards (e.g. Dwarf board) is achieved using the MODBUS protocol. In MODBUS, there are two types of devices: the master and the slave, also known, respectively, as client and server. On Original Prusa XL firmware, the master is the XLBuddy, and each slave is called puppy.
If necessary, typically after a firmware update, the printer flashes the needed firmware files onto the flash memory of the peripheral boards. If this procedure fails, the printer will show the message: "Puppy # flash writing failed".
Error name: Puppy write flash err
Error code: #17519
The error message will include the name of the puppy that had the issue.
Download the firmware and if necessary the bootloader, and transfer it to your USB drive. Make sure to unmount the drive from your operating system before physically removing it.
Insert the USB drive back into the printer and reboot the printer using the reset button directly next to the knob to initiate the flashing procedure. In case the procedure does not start, reboot the printer again by pressing the same reset button, and while the printer is booting up, press once the rotating knob.
Access the XLBuddy and Sandwich boards from the rear of the printer, by loosening the screws shown in the picture below.