$work has an ultimaker 2, I wanted to upgrade it and this would be vastly simpler with control over the firmware.
Ultimaker firmware
The stock ultimaker firmware situation is very confusing.
Ultimaker have three github repos for three types of printer according to Ultimaker employee ckielstra, and they may have more by now, they've released more printers.
My printer had 2.6 firmware on it, and I never figured out which branch was for the UM2 let alone that version. I just gave up and am hoping that if I ever want stock firmware for some reason cura will just hand me something useful.
Marlin
Running 2.0.9.3 for now because it's the most recent tag.
It's built with pio which is super convinent.
pio run -e mega2560ext
firmware is now at .pio/build/mega2560ext/firmware.hex
Starting Config
Someone was nice enough to share a UM2 config for Marlin
Flashing
Ultimaker forum user amedee gives us correct avrdude flashing arguments:
avrdude -C /etc/avrdude.conf -v -p atmega2560 -c wiring -P "/dev/ttyACM0" -b 115200 -D -U "flash:w:firmware.hex:i"
Or octopi firmware updater plugin, the AVR programmer type is "wiring".
Running
Out of the gate the menu works, it moves. Doesn't reach temp though, just https://cdn.discordapp.com/attachments/400424470327721985/929252930052317204/unknown.png Looks like a PID issue but I don't want to learn PID tuning tonight.
Octoprint recommends
HOST_ACTION_COMMANDS so I enabled HOST_PAUSE_M76 and HOST_PROMPT_SUPPORT.
It means the printer can tell octoprint to pause.