Emergency Stop killing power without killing Pi/Reprap Firmware

Cheetah

I'm trying to sort out my emergency stop situation and I have a possibly appealing option.
I'd like to E-Stop without killing the UI at all which means very fast debugging and getting going again.

It's recommended to kill all the power which is certainly safe, but rather inconvenient if all the software goes down.
The problem with non-power killing methods is it appears Reprap Firmware can't interrupt the currently running command, so if there's a long move it'll continue moving before stopping.

What I'm wondering is what is the behaviour of Reprap Firmware if I power the 5v rail from the SBC, and emergency stop kills 24v power?

Doing it that way should be ideal:

Motors stop immediately
The Pi and Reprap Firmware stay alive so no rebooting

However does Reprap Firmware detect the loss of 24v power? If the spindle isn't turned off then that might be less than ideal and require additional circuitry to handle.
And what does it do to the current job? Does it pause it/stop it or try and keep running it?

If that can be answered that would save me from wiring everything up in that configuration then finding out there's a problem with it.

fractalengineer

@Cheetah

I use the kill all estop in series to the mains, but if you were to try something more selective you could:

1-have 2 power supplies; one 24V for your duet VIN, one for 5V usb on the duet

2-Most e-stops have 2 modes; NC and NO.

On the NC you would wire the mains powering your 24V PSU and SSR (if using an AC bed)
Wire the NO to the duet and assign as software estop

This way pushing the estop would kill the heated bed and duet vin, trigger the software estop, but leave the 5V duet power through USB untouched

The one issue though would be that it would also kill your fans, including the hotend fan that may allow residual heat to creep up

There is a chinese board out there that has a separate VIN for the steppers but I can't remember which one

plasmino

In my opionion, the best option would be to configure you e-stop button as a trigger.
https://duet3d.dozuki.com/Wiki/Connecting_an_Emergency_Stop#Section_Making_a_button_do_what_you_want

You could use M581 to configure an external trigger binded to a trigger#.g macro. The macro would be triggered by your e-stop and run the piece of gcode, in wich you may put a pause/stop command and a M18 to turn off each motor so they will move freely.
I'm not sure, but I think with M18 the firmware simply sets the enable pin to the stepper drivers as low, so only the power between drivers and motors is cut.
If you are ok with it you only need to wire the endstop to a IO pin or to a not used endstop pin.