These were commits 9dbfa7217e0de8b140846ab480d6b4a7fc9b6791 and
2b596cb05e621ed822071486f812eb334328267a.
There are several reasons why this new approach didn't work out well:
- The machine coordinate system is lost on relative movements.
OK, we could keep tracking it, but this would mean even more
code, so even more chances for bugs.
- With the lost coordinate system, no software endstops are possible.
- Neither of X, Y, Z will ever overflow.
- If a movement planner would appear one day, he'd have to handle
relative movements as well. Even more code duplication.
Instead of converting them to absolute first, then back to
relative and having all the fuzz with working on the queue's
start vs. working at the queue's end, mark a movement as relative
and use this directly.
This is a intrusive patch and for now, it's done for the X axis only.
To make comparison with the former approach easier ...
The advantages of this change:
- Converting from mm to steps in gcode_parse.c and back in dda.c
wastes cycles and accuracy.
- In dda.c, UM_PER_STEP simply goes away, so distance calculations
work now with STEPS_PER_MM > 500 just fine. 1/16 microstepping
on threaded rods (Z axis) becomes possible.
- Distance calculations (feedrate, acceleration, ...) become much
simpler.
- A wide range of STEPS_PER_M can now be handled at reasonable
(4 decimal digit) accuracy with a simple macro. Formerly,
we were limited to 500 steps/mm, now we can do 4'096 steps/mm
and could easily raise this another digit.
Disadvantages:
- STEPS_PER_MM is gone in config.h, using STEPS_PER_M is required,
because the preprocessor refuses to compare numbers with decimal
points in them.
- The DDA has to store the position in steps anyways to avoid
rounding errors.
Markus Hitter
Ben Gamari
Bas Laarhoven
Michael Moon
Markus Amsler