Pause and resume after power off??

I just watched a review of the Dynamo3D one pro made by Thomas Sanladerer, and I was surprised to see a really cool feature developed by that company that let's you pause, turn off the printer and resume printing even after a few days. Now, I was wondering, what would it take to implement this in the great RepRapFirmware as well? A way to save the current buffer and position on a file onto the SD card and if such "resume file" is found at boot time, it can than activate the "Resume" button in the web interface where the user can click it... Now, position of the print head must remain unchanged during the whole pause interval, just thinking about microstepping and jumping on the full step on power-off. What can be done about that? Can the firmware know or compute where the full steps are on the axis and park on the full steps position only? Or maybe it does not even affect the final quality of the print to be a problem to begin with. The Dynamo3D is fully closed source, there is no way we can find out how they implemented this function, if they skipped the microstepping part or they found a workaround or not... but it would definitely be a great feature to have!

This is already on the firmware wish list for the Duet WiFi. Obviously it is only possible if you can home the printer when there is a print on the bed (as is normally the case for a delta printer), or you can power down the motors in such a way so that they will power up again in exactly the same position.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Quote
dc42
This is already on the firmware wish list for the Duet WiFi. Obviously it is only possible if you can home the printer when there is a print on the bed (as is normally the case for a delta printer), or you can power down the motors in such a way so that they will power up again in exactly the same position.

That is nice, but this means that the rest of us, with older boards won't benefit from this ?

Now, regarding the motor positions. My printer is able to home with a "loaded" bed, I could implement this in the g-code if I plan from the very beginning to split the print on different days. But for others that cannot do the homing with a loaded bed, wouldn't be possible to start counting the steps after enabling the stepper up to hitting the homing switch ? This way the full steps coordinates can be calculated (theoretically, maybe no practically?) and used in the pause routine. Just a thought..