robustify python USB discovery/communication

tools/odrive/usbbulk_transport.py

@@ -35,6 +35,12 @@ class USBBulkTransport(odrive.protocol.PacketSource, odrive.protocol.PacketSink)
     return string
 
   def init(self):
+    # Under some conditions, the Linux USB/libusb stack ends up in a corrupt
+    # state where there are a few packets in a receive queue but a call
+    # to epr.read() does not return these packet until a new packet arrives.
+    # This undesirable queue can be cleared by resetting the device.
+    self.dev.reset()
+
     try:
       if self.dev.is_kernel_driver_active(1):
         self.dev.detach_kernel_driver(1)
@@ -106,7 +112,7 @@ class USBBulkTransport(odrive.protocol.PacketSource, odrive.protocol.PacketSink)
       else:
         # Try resetting halt/stall condition
         try:
-          self.epw.clear_halt()
+          self.epr.clear_halt()
         except usb.core.USBError:
           raise odrive.protocol.ChannelBrokenException()
         # Retry transfer

tools/odrive/utils.py

@@ -73,11 +73,15 @@ class Event():
     """
     Alternative to threading.Event(), enhanced by the subscribe() function
     that the original fails to provide.
+    @param Trigger: if supplied, the newly created event will be triggered
+                    as soon as the trigger event becomes set
     """
-    def __init__(self):
+    def __init__(self, trigger=None):
         self._evt = threading.Event()
         self._subscribers = []
         self._mutex = threading.Lock()
+        if not trigger is None:
+            trigger.subscribe(self.set())
 
     def is_set(self):
         return self._evt.is_set()
@@ -120,7 +124,18 @@ class Event():
             self._mutex.release()
 
     def wait(self, timeout=None):
-        return self._evt.wait(timeout=timeout)
+        if not self._evt.wait(timeout=timeout):
+            raise TimeoutError()
+
+    def trigger_after(self, timeout):
+        """
+        Triggers the event after the specified timeout.
+        This function returns immediately.
+        """
+        def delayed_trigger():
+            if not self.wait(timeout=timeout):
+                self.set()
+        threading.Thread(target=delayed_trigger, daemon=True).start()
 
 def wait_any(*events, timeout=None):
     """