Add Stepping Status to emcmodule

[satiowadahc]

I don't see another way of doing this, but currently I can't see any feedback in any UI that shows the current Single Block mode (Stepping) or not.

It seems to be a flag you send with command.AUTO(AUTO_STEP) and you can just remember in your UI you set the flag...? I prefer polling to know the real answer.

[satiowadahc]

I even added documentation for once :)

[rmu75]

IMO the stepping flag should also be added to EMC_TRAJ_STAT::update here https://github.com/LinuxCNC/linuxcnc/blob/master/src/emc/nml_intf/emc.cc#L1688

[andypugh]

Not wanting to distract with trivialities, but "singlestep" would disambiguate from anything stepper-motor related.
(I initially assumed the latter when this PR appeared)

[satiowadahc]

I was originally trying to add it in update. But was struggling to get it to work properly . I'd welcome pointers in the right direction.

I'm OK of changing the name. The amount of "status" variables that are different status objects made this way harder than expected.

[rmu75]

Can you elaborate what didn't work?

I just tried this PR and added this line

index 0b4117b229..d1d6e3f68b 100644
--- a/src/emc/nml_intf/emc.cc
+++ b/src/emc/nml_intf/emc.cc
@@ -1702,6 +1702,7 @@ void EMC_TRAJ_STAT::update(CMS * cms)
     cms->update(queueFull);
     cms->update(id);
     cms->update(paused);
+    cms->update(stepping);
     cms->update(scale);
     cms->update(rapid_scale);
     EmcPose_update(cms, &position);

It compiles without issues, runtests completes without error Runtest: 272 tests run, 272 successful, 0 failed + 0 expected, 4 skipped, 0 shmem errors. Didn't really check if the flag is doing what it's intended to though.

[satiowadahc]

The stepping variable wasn't updated.

[andypugh]

Having thought more on this, can the name of the flag be changed? "stepping" is ambiguous. "single-step" or a variant would be better.