Yet another Marlin for M2 fork

[jsc]

I realize several people have their own tracking forks of Marlin, but they're all to add support for hardware I don't have and none are for the dual setup, so here's mine: https://github.com/jinschoi/Marlin

Fork of latest Release branch (1.0.2) with support for v4 dual extruders. Changes from stock:
Configuration set up for M2, using settings blindly transferred over one by one from MakerGear's M2_Dual_Extruder_Marlin firmware. Only settings not taken directly were to enable the auto extruder fan and put in my own PID values.
temperature.cpp modified to workaround a compiler bug with dual extruders using the least invasive "fix" from here: https://github.com/MarlinFirmware/Marlin/issues/1523
stepper.cpp modified to add a workaround for skipped steps during fast moves exacerbated in newer versions of the Arduino IDE.

I haven't given it a thorough testing yet.

[jimc]

Ok this is good jin and thanks. Now to change this from a dual firmware to a single is it just a matter of turning off tool 1? any special changes need to be made for that to happen?

[jsc]

To convert it to a plain jane single extruder version, yes, set EXTRUDERS to 1, and also set EXTRUDER_1_AUTO_FAN_PIN from 6 to -1 to turn off the auto extruder fan activation on the non-existent second extruder (Configuration_adv.h).

For the E3D, you will want to do whatever you do for that as well (extruder current and PID settings, thermistor table switch).

[jsc]

Oops, missed the EEPROM support setting, turned that on just now.

[jsc]

Aaaand I got the missed steps workaround wrong, so I had to fix that.