movement pauses during the execution of an MCode

I think you have a lot of things very confused

correct

Do you have a machine configuration that "mostly" works for you except for the pauses in motion when you try to change the extruder feed using M3Snnn?

also correct,
it works fine but my thesis work is to improve the printing: by making so i made a bunch of functions that calculate the speed of the estruder in all the planned path, then using another algorithm i calculate the best pressure for an uniform extrusion.
I then need to change the pressure (in the G-code) in the points where the speed change over a certain threshold (in the change of direction). 
Here comes the problem because when i use the "M3 Snnn"  that change the voltage output, that change the pressure of extrusion, the robot stops and this generate an accumulation on the printing path.

i included all the attachments i got for a complete view 
thank you for all the help

You could try to manipulate the analog spindle output of the 7i76 with the float value in
"motion.analog-out-00".
So either try to feed your desired "speed" directly into this:
net spindle-output => hm2_7i80.0.7i76.0.0.spinout

Or use the "halui.spindle.0.override" pins
linuxcnc.org/docs/html/man/man1/halui.1.html

Note that, if I remember correctly, the 7I76 will only output the analog signal if hm2_7i80.0.7i76.0.0.spinena is true.

edit: personally I would try the override first

thank you for the answer!
sorry for my late reply
for what i read i have understood that the override can provide an increment or decrement of actual pin value (am i right?), what i need is to change the value multiple time with some pre-calculated numbers,
for this reason i think i could not follow your personal suggestion
by the way i think the first way you exposed could be the right one! :side:
i'm now studying the HAL file in order to "manipulate the analog spindle output with the float value in motion.analog-out-00" as you said
i already have the command for "net spindle-output => hm2_7i80.0.7i76.0.0.spinout" in the HAL so i guess i need to change the link for "spindle-output" that now is on the PID to the analog.motion

(now is "net spindle-output <= pid.s.output")

we got it guys!!
thanks for all your help and time!

the Gcode now starts with an M3 M67 E0 Qxxx so the spindle is activated and the speed is modified by the pin 00, when i need to change the pressure i just M67 E0 Qxxx and it changes without stopping the motion
i just changed 1 line in the .hal file:
it was : net spindle-output <= pid.s.output
it became : net spindle-output <= motion.analog-out-00
(replies will follow if something don't go as planned)