M function during move

Randomly. Now an external script is running that sends linuxcnc rsh command and switch output. To do this, I calculate the time at the script level. But if it is included in the G-code, it will be easier to calculate.

What about the distance to the end of the path, is that a constant value or does that change?

[edit]
I mean the "t" or "S" value in your picture.

Constant value. But to find this value need to conduct an experiment to find an acceptable. If calculate in script level I need to change a lot of parameters. If calculate in G-code only one


UPD
motion.distance−to−go It's that me need!!!

Is there a similar variable for time?

So, if you write a hal component that constantly switches a pin at the desired distance before reaching the end point you could use M64 P0 with an and2 block to "enable that signal to go out and then M65 P0 to disable the output again. Maybe you could even find a way to automatically disable the output after motion.distance-to-go as reached 0.
Your S value could be defined in the INI or in the GUI.

Just an idea.

That's what I wanted to do!
What about time variable?

UPD I can motion.distance-to-go div to motion.current-vel but isn't include aceleration