M66 handled in planner & stepper block

[joharymanitra]

Hello,

Would it be possible to handle M66 cmd (Wait on Input) in planner and as a stepper block (without movement) so the controller will already prepare next stepper movement while waiting for the input state change? This will make the controller more reactive to input handling.

Best regards

[terjeio]

You mean speculative execution where the result is guessed and the related code path its taken? And if the guess is wrong it drops the queued motion, rewinds to the M66 and take the correct path?

[joharymanitra]

I'm not sure choosing between two paths is required. I think that just the ability to wait for input change is enougth to cover most real time motion syncronizing requirement. If the delay is not infinite, for example M66P0L4Q0.5, i think the gcode excecution can just stop and go into error state as the expected event did not occur within the specified timeout. If the event occurs, the controller excecute the next block

[terjeio]

From LinuxCNC M66 description:

"M66 wait on an input stops further execution of the program, until the selected event (or the programmed timeout) occurs."

What happens on a timeout has to be coded for, and there may be two or three code paths for digital input returning a value:

M66P0L4Q3600
o100 if [#5399 EQ -1]
(abort, Timeout waiting for input)
o100 elseif [#5399 EQ 1]
G1X100F300
o100 else 
G1X50F200
o100 endif
Y200
...

What is the expected event in the above code? The first one causing the abort? And if different the code has to be rewound to the first statement after the M66. Not easy to implement, you can try?
...

[joharymanitra]

Yes the first one causing abort.
I see, linux CNC says it's can't be used in real time as it choose between two paths according to the input state. Yeah not easy to implement. I'll try