If you could change the microstepping on the 4.2.2/4.2.7, what changes would need to be made to the firmware?

[Reggi3]

I don't know much about marlin, I've been using jyers firmware as it's the best for ender 3 v2 (imho) but I could do with some help understanding some things and configuring things correctly. Here's a bit of background...

I've just done the 4.2.2 Linear Advance mod by Wong Sy Ming and I noticed that it sets microstepping to 16 in the firmware, on an unmodded board, this is set by the MS1 and MS2 pins on the tmc2208 chip being pulled high, so the only way to increase the microstepping on the 4.2.2 is is via software by doing the linear advance mod. The mod enables TMC uart access on the extruder, which has a default configuration in the marlin/jyers configuration files. Does anyone know if the TMC uart configuration is correct for the ender 3 v2? For instance, #define CHOPPER_TIMING CHOPPER_DEFAULT_12V is set in Configuration_adv.h but I think this should be set to #define CHOPPER_TIMING CHOPPER_DEFAULT_24V instead? Are there any other settings I need to look at in the config files?

I've also checked the 4.2.7 board and it's using a TMC2225 chip, totally different footprint, you can set microstepping to 32 via MS1/MS2 but it's hard wired to Hi/Lo (16 mSteps) to match the 4.2.2 configuration.

This might sound like an odd question but what advantage would there be to doubling (or higher) the micro stepping on any axis? If there is an advantage, what changes would be needed in the firmware, would it simply be a case of changing steps/mm for a given axis?

I ask this because, as well as marlin, I don't have much experience with stepper motors or stepper motor drivers and it's a very simple mod that looks like it could double (or more) the printer resolution. I don't know how that would impact on torque, current, heat, print times or overall performance or even whether it's necessary on a particular axis, for instance, Z axis is already 400 steps/mm.

I mentioned the 4.2.2 board in the title, with uart access to the motor driver chips, you can set the microstepping up to 256, which is obviously a much bigger change in resolution, you also gain control of other functions on the chips, like swapping between stealthchop and spread cycle modes, being able to set the max current for any axis via software and also setting the holding current.

There is also a 'spread' pin on the tmc2225, which is tied low (Stealthchop mode), also matching the 4.2.2 configuration, I haven't done the Linear Advance mod on the 4.2.7 board but having had a good look at the PCB for both boards, they're essentially laid out in the same manner, so it should be possible.

I have more information to share and more questions to ask but I think that will do to get things started... 😄

[Reggi3]

I have some answers to my questions...

1. It appears that increasing microsteps doesn't necessarily increase resolution but it will increase the load on the printer.

2. #define CHOPPER_TIMING CHOPPER_DEFAULT_12V does indeed need to be changed to #define CHOPPER_TIMING CHOPPER_DEFAULT_24V to match the input voltage of our printer