Firmware for running a Prusa MK3(s) printer with the 0.9 degree stepper motors from here
https://www.omc-stepperonline.com/en/nema-17-bipolar-0-9deg-36ncm-51oz-in-0-9a-5-4v-42x42x40mm-4-draehte-17hm15-0904s
mounted on the X and Y axis.
This firmware is not configured for doubling the horizontal resolution of the printer, instead it configures half the number of microsteps so that the horizontal resolution stays the same as stock.
Its sole purpose is to eliminate the VFAs (vertical fine artifacts) produced by the stock 1.8 degree Prusa motors.
It MUST ONLY be used with exactly the aforementioned 0.9° steppers!
YOU MAY USE IT AT YOUR OWN RISK!
I WON'T TAKE ANY RESPONSIBILITY IN ANY FORM OR MANNER FOR ANY DAMAGE WHATEVER KIND AND NATURE BY USING ANY PART OF THIS REPOSITORY EITHER AS INTENDED OR IN ANY OTHER WAY!
That said I've successfully been using this firmware on my Prusa MK3 for some years now, without a trace of an issue and haven't yet heard about any tragic incident caused by using it as intended.
There are flashable files available for different extruder setups, namely:
MK3 & Stock Extruder
MK3s(+) & Stock Extruder
MK3s(+) & Bondtech BMG (Bondtech Extruder Upgrade for Prusa MK3s(+)) with E3Dv6 compatible Hot End
MK3s(+) & Bondtech BMG (Bondtech Extruder Upgrade for Prusa MK3s(+)) with SE Mosquito Hot End
MK3s(+) & Bondtech LGX Shortcut Copperhead
MK3s(+) & Bondtech LGX Shortcut Mosquito
After flashing the firmware, you MUST factory reset the printer and clear all data.
https://help.prusa3d.com/article/factory-reset-mk2s-mk2-5s-mk3s_2216
After that you have to rerun the self test, XYZ-calibration and the Z-offset adjustment.
If you don't want to cut off and reuse the controller board connectors from the original motors, by soldering them to the new ones, you will need to buy a pair of them e.g. from here:
https://www.3djake.de/bondtech/dupont-kabel-mit-sicherungsclip
UPDATES for 3.12.2_shyblower_1:
I've tuned stallguard and coolstep thresholds to make slightly overtightened belts and not so smoothly running bearings not trigger crash detections too easily.