fixes for flamesample

- fixes in SwitchDrive
- increase range when reading is zero in autorange
- add debugging log msgs

frappy_psi/ls372.py

@@ -235,6 +235,9 @@ class ResChannel(Channel):
             return None
         result = float(self.communicate('RDGR?%d' % self.channel))
         if result == 0:
+            if self.autorange:
+                rng = int(max(self.minrange, self.range))  # convert from enum to int
+                self.write_range(min(self.MAX_RNG, rng + 1))
             return None
         if self.autorange:
             self.fix_autorange()
@@ -251,8 +254,10 @@ class ResChannel(Channel):
                             lim -= 0.05  # not more than 4 steps at once
                         # effectively: <0.16 %: 4 steps, <1%: 3 steps, <5%: 2 steps, <20%: 1 step
                 elif rng < self.MAX_RNG:
+                    self.log.debug('increase range due to error %d', rng)
                     rng = min(self.MAX_RNG, rng + 1)
                 if rng != self.range:
+                    self.log.debug('range change to %d', rng)
                     self.write_range(rng)
                     self._last_range_change = now
         return result