M571 Improvements - Advance Output
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I think the addition of two parameters to the M571 command would be really helpful for pneumatic based systems.
Most pneumatic systems suffer from a lag between the time the gpio pin associated with the M571 pin goes high and the time extrusion begins. This is generally due to mechanical compliance in the hardware.
If a parameter could be added that sets the output high in advance of a move with extrusion (usually less than 500 milliseconds)) it would account for the time it takes the system to reach adequate pressure. Similarly, if the pin could be driven low before the move with extrusion ends, it would help prevent ooze during de-pressurization.
Right now I am managing it with a "extra prime amount" when slicing in Cura, but It is problematic because it only works after a retraction.
Pressure advance as currently structured does not meet the need because it only functions during the extrude command, not in advance of it.
Thanks
