Add a parameter Snnn to M92 that indicates the microstepping factor

[wilriker]

This closes my request at: https://forum.duet3d.com/topic/8225/m92-parameter-to-indicate-microstepping

I was too impatient again. ;-)

I chose the parameter to be Fnnn just because I wanted to avoid Mnnn because of M-codes and X or U are already taken by axis names. So this is microstepping-Factor.

[dc42]

Thanks for your PR. Suggestions for improvement:

• I don't like the use of F for the microstepping, F rarely means anything other than feed rate. How about S for Stepping instead?
• Please use a uint32_t and GetUIValue to get the value of the new parameter, instead of int32 and GetIValue
• The interface to Platform is already rather fat and I don't like creating a new member function that is almost a duplicate of the old one. I suggest one of the following:
  (a) do the microstep conversion calculation within the M92 code in GCodes2.cpp instead of in Platform. You can use the existing Platform::GetMicrostepping function to fetch the current microstepping of the drive.
  (b) pass the new microstepping value as an extra parameter to Platform::SetDriveStepsPerUnit, or pass 0 if it wasn't specified. Then Platform::SetDriveStepsPerUnit can do the conversion if 0 wasn't passed.

[wilriker]

I had a hard time thinking of which parameter to actually use. I was also hesitant to use F due to its usual meaning of feed rate but also S seemed not the ideal solution to me (I would have preferred X or U but they are both reserved for axis names). Anyway, I changed it as proposed to S.

Also changed to uint32_t. I would have chosen that in the first place but must have missed that it exists.

And I decided that I unify the two SetDriveStepsPerUnit methods because it had the least code duplication since in M92 handling there are separate code paths for drives and extruders I would have to do the calculation in both loops. This way it is still done for each drive but just in one place in the source.

[dc42]

Thanks for making those changes. Please re-submit your PR with target branch 'dev' because that is the branch I am now using for development.

[wilriker]

Done.

[wilriker]

For sake of completeness: I added this parameter to reprap.org

[dc42]

Thanks!