Jennyprinter: sporadic error, print stops halfways

[ErwinRieger]

Jennyprinter: sporadic error, print stops halfways

Firmware seems to run normally, just the processing of the stepbuffer stops. Maybe irq-related.

[ErwinRieger]

There was an error in the computation of RawStepData (sign-error).

Fixed in 84e985e (in next branch).

Will close this issue when merged into master.