make syncing happen at the right time (#874)

qcodes/instrument_drivers/ZI/ZIUHFLI.py

@@ -260,7 +260,8 @@ def add_post_trigger_action(self, action: Callable) -> None:
         has been armed. The action must be a callable taking zero
         arguments
         """
-        self._scopeactions.append(action)
+        if action not in self._scopeactions:
+            self._scopeactions.append(action)
 
     @property
     def post_trigger_actions(self) -> List[Callable]:
@@ -271,7 +272,7 @@ def prepare_scope(self):
         Prepare the scope for a measurement. Must immediately preceed a
         measurement.
         """
-        #
+
         log.info('Preparing the scope')
 
         # A convenient reference
@@ -471,15 +472,18 @@ def get(self):
                 # scope.finish is always called even if the
                 # measurement is interrupted
                 self._instrument.daq.setInt('/{}/scopes/0/single'.format(self._instrument.device), 1)
-                self._instrument.daq.sync()
 
-                scope = self._instrument.scope  # There are issues reusing the scope.
+
+                scope = self._instrument.scope
                 scope.set('scopeModule/clearhistory', 1)
 
                 # Start the scope triggering/acquiring
-                params['scope_runstop'].set('run')  # set /dev/scopes/0/enable to 1
+                # set /dev/scopes/0/enable to 1
+                params['scope_runstop'].set('run')
+
+                self._instrument.daq.sync()
 
-                log.info('[*] Starting ZI scope acquisition.')
+                log.debug('Starting ZI scope acquisition.')
                 # Start something... hauling data from the scopeModule?
                 scope.execute()
 
@@ -490,7 +494,10 @@ def get(self):
                 starttime = time.time()
                 timedout = False
 
-                while scope.progress() < 1:
+                progress = scope.progress()
+                while progress < 1:
+                    log.debug('Scope progress is {}'.format(progress))
+                    progress = scope.progress()
                     time.sleep(0.1)  # This while+sleep is how ZI engineers do it
                     if (time.time()-starttime) > 20*meas_time+1:
                         timedout = True