tmc2130: Rework current selection to prefer vsense=1

It is preferable to program the tmc drivers with an irun (or cs)
setting near 31, as otherwise the driver may have reduced microstep
precision.  It was possible for the driver to be programmed with
irun=16 or irun=17 when it could have been configured with irun=31
with vsense=1 instead.  This would occur on tmc2130/tmc2208/tmc2209
drivers for values around 0.900 to 1.000 amps (when using a typical
sense_resistor settings of 0.110 Ohms).

Change the code to prefer using vsense=1 to avoid this issue.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

1 files changed, 17 insertions, 8 deletions

diff --git a/klippy/extras/tmc2660.py b/klippy/extras/tmc2660.py
index c0d8fa9b..e873c608 100644
--- a/klippy/extras/tmc2660.py
+++ b/klippy/extras/tmc2660.py
@@ -136,17 +136,26 @@ class TMC2660CurrentHelper:
 
     def _calc_current_bits(self, current, vsense):
         vref = 0.165 if vsense else 0.310
-        cs = int(32 * current * self.sense_resistor * math.sqrt(2.) / vref
-                 - 1. + .5)
+        sr = self.sense_resistor
+        cs = int(32. * sr * current * math.sqrt(2.) / vref + .5) - 1
         return max(0, min(31, cs))
 
+    def _calc_current_from_bits(self, cs, vsense):
+        vref = 0.165 if vsense else 0.310
+        return (cs + 1) * vref / (32. * self.sense_resistor * math.sqrt(2.))
+
     def _calc_current(self, run_current):
-        vsense = False
-        cs = self._calc_current_bits(run_current, vsense)
-        if cs < 16:
-            vsense = True
-            cs = self._calc_current_bits(run_current, vsense)
-        return vsense, cs
+        vsense = True
+        irun = self._calc_current_bits(run_current, True)
+        if irun == 31:
+            cur = self._calc_current_from_bits(irun, True)
+            if cur < run_current:
+                irun2 = self._calc_current_bits(run_current, False)
+                cur2 = self._calc_current_from_bits(irun2, False)
+                if abs(run_current - cur2) < abs(run_current - cur):
+                    vsense = False
+                    irun = irun2
+        return vsense, irun
 
     def _handle_printing(self, print_time):
         print_time -= 0.100 # Schedule slightly before deadline