diff --git a/bstrd/bscache.py b/bstrd/bscache.py
index c8dbfac..a667ae7 100644
--- a/bstrd/bscache.py
+++ b/bstrd/bscache.py
@@ -47,6 +47,19 @@ class BSCache:
                     yield data
 
 
+    def start(self):
+        self.pt.start()
+
+        while self.data is None:
+            print("dropping empty data")
+            next(self)
+
+        while not self.channels.keys() <= self.data.keys():
+            missing = self.channels.keys() - self.data.keys() - FIXED_CHANNELS
+            print("dropping data that is missing channel(s):", sorted(missing))
+            next(self)
+
+
     def stop(self):
         self.pt.stop()
 
@@ -68,19 +81,10 @@ class BSCache:
 
 
     def update_source_multiple(self, chans):
-        self.pt.stop()
+        self.stop()
         print("add channels", sorted(chans))
         self.channels.update(chans)
-        self.pt.start()
-
-        while self.data is None:
-            print("dropping empty data")
-            next(self)
-
-        while not chans.keys() <= self.data.keys():
-            missing = self.data.keys() - chans.keys() - FIXED_CHANNELS
-            print("dropping data that is missing new channel(s)", sorted(missing))
-            next(self)
+        self.start()
 
 
     def get_var(self, name, modulo=None, offset=None):
@@ -93,18 +97,10 @@ class BSCache:
 
 
     def update_source(self, name, cfg):
-        self.pt.stop()
+        self.stop()
         print("add channel", name)
         self.channels[name] = cfg
-        self.pt.start()
-
-        while self.data is None:
-            print("dropping empty data")
-            next(self)
-
-        while name not in self.data:
-            print("dropping data that is missing new channel:", name)
-            next(self)
+        self.start()
 
 
     def flush(self):