Controlling Prusa Mini over Serial Line, Questions. M24, M73, M118, M155  

Controlling Prusa Mini over Serial Line, Questions. M24, M73, M118, M155

Hello,
I am trying to see how far I can push controlling my Prusa Mini over the serial line (Micro USB port).

I went so far that I see regular temperature update on the serial line as described in the documentation of the M105 and M155 commands:

T:55.09 /170.00 B:31.20 /60.00 A:62.09 /0.00 @:117 B@:127 W:?
T:58.16 /170.00 B:31.67 /60.00 A:62.11 /0.00 @:115 B@:127 W:?
echo:busy: processing
T:61.18 /170.00 B:32.11 /60.00 A:62.08 /0.00 @:113 B@:127 W:?
T:63.99 /170.00 B:32.81 /60.00 A:62.08 /0.00 @:112 B@:127 W:?

After the print starts, this switches to position updates.

I was expecting to get a little bit more information as I wanted to implement something similar to Octolapse, e.g. trigger a camera on every layer change. So I added a custom g-code to print a command on the serial line using the M118 gcode. This is what I added to my slicer config:

;BEFORE_LAYER_CHANGE
G92 E0.0
;[layer_z]
M118 Take Picture

However, I do not see those messages on my serial line.

I also tried polling the printer for some status using the M73 command, dispatched from the serial connection. According to the documentation, this should print the status if given with no arguments, but all I get back is "ok".

I could successfully query the printer for the files on the USB Stick by using the M24 command, so sending commands to the printer from my side seems to work.

Questions:

1. How do I send a custom message from the printer on the serial line to my connected device? M118 does not seem to work. Did anyone had success with this so far?
2. How do I get the progress on the serial line? M73 does not seem to work either, all I get back is "ok".
3. I wanted to change the regular updates according to the docs of the M155 command. The docs mention a bitflags argument mentioned, but nothing about the syntax or examples: https://help.prusa3d.com/ja/article/supported-g-codes_112173
   I tried 7, 111, 1 and 100 but all I get back from the printer is another "ok" and no obvious change in behavior.
4. Is there some kind of debug/more verbose mode for the serial line?
5. Any more ideas how to get the z-change event? I see that there is a) a g-code for a camera trigger but disabled in the prusa firmware b) a suitable pin on the extension port of the buddy board, however, with a proprietary connector (2.00 mm). 

I am using the beta release of the firmware with WiFi support

Best regards,

Axel Jäger