Add frequency option to AFMPiezo.move_to_pos_or_def.

diff --git a/pypiezo/afm.py b/pypiezo/afm.py
index bfc9585e9a6edbc5c8a5fb208e7de2e318a8e5e1..76ee928efd74f0eaf4923d379e3983d9d5154d82 100644 (file)
--- a/pypiezo/afm.py
+++ b/pypiezo/afm.py
@@ -17,12 +17,13 @@
 
 "Control of a piezo-based atomic force microscope."
 
+import time as _time
+
 import numpy as _numpy
 
 try:
     import matplotlib as _matplotlib
     import matplotlib.pyplot as _matplotlib_pyplot
-    import time as _time  # for timestamping lines on plots
 except (ImportError, RuntimeError), e:
     _matplotlib = None
     _matplotlib_import_error = e
@@ -168,12 +169,17 @@ class AFMPiezo (_base.Piezo):
         return self._deflection_channel().subdevice.get_dtype()
 
     def move_to_pos_or_def(self, axis_name, position=None, deflection=None,
-                           step=1, return_data=False, pre_move_steps=0):
+                           step=1, return_data=False, pre_move_steps=0,
+                           frequency=None):
         """TODO
 
         pre_move_steps : int
             number of 'null' steps to take before moving (confirming a
             stable input deflection).
+        frequency : float
+            The target step frequency in hertz.  If `Null`, go as fast
+            as possible.  Note that this is software timing, so it
+            should not be relied upon for precise results.
         """
         if position is None and deflection is None:
             raise ValueError('must specify position, deflection, or both')
@@ -220,6 +226,9 @@ class AFMPiezo (_base.Piezo):
             if aquire_data:
                 def_array.append(current_deflection)
                 pos_array.append(self.last_output[axis_name])
+        if frequency is not None:
+            time_step = 1./frequency
+            next_time = _time.time() + time_step
         # step in until we hit our target position or exceed our target deflection
         while (self.last_output[axis_name] != position and
                current_deflection < deflection):
@@ -237,6 +246,11 @@ class AFMPiezo (_base.Piezo):
             if aquire_data:
                 def_array.append(current_deflection)
                 pos_array.append(self.last_output[axis_name])
+            if frequency is not None:
+                now = _time.time()
+                if now < next_time:
+                    _time.sleep(next_time - now)
+                next_time += time_step
 
         log_string = (
             'move to position %d or deflection %g on axis %s complete'