Snapmaker 2 doesn't understand GCodes about removable storage, such as M21 (initialize SD) #308

See Marlin docs > gcode > M21.

Setup: I have the Snapmaker 2 A350, configured for 3D printing, connected over USB to an Octoprint server (on a Raspberry Pi 4). It seems to be up to date as of 2023-09-23, will update with firmware version if requested.

Trying to access flashdrive files from Octoprint. The process begins with sending M21 (init_SD), and the printer states it doesn't understand the command.

Send: M21
Recv: echo:Unknown command: "M21"
Recv: ok

Other SD card related commands to investigate similarly:

• M20; List SD files
• M21; Initialize SD
• M22; Release SD
• M23; Select SD file
• M24; Start/Resume print from SD
• M25; Pause SD Print
• M26; Set SD Position (I'm assuming it means line number?)
• M27; Report SD print progress
• M28; Start SD Write (transcribe commands to file instead of printing)
• M29; Stop SD Write
• M30; Delete SD File
• M32; Select file and print (useful for importing sub-scripts, such as GCode that every print should begin with)
• M33; Get long path (What file are we printing right now?)
• M34; SD Card Sorting options
• M524; Abandon SD print, turn off heaters

// tangent, but, while discussing gcode support, we could also use M117; Set LCD Message. It just says OK and doesn't show anything on the display. I guess because the screen isn't part of the controller, but, come on, it's the only screen we have, it'd be great to have that patched. But this should be a separate bug report