tuanml · December 26, 2018 15:20 · Sep 19, 2014 · Sep 19, 2014 · Sep 18, 2014
diff --git a/usb_reset.py b/usb_reset.py
@@ -46,8 +46,10 @@ def send_reset(dev_path):
                    See get_teensy for example of how to obtain this.
     """
     fd = os.open(dev_path, os.O_WRONLY)
-    fcntl.ioctl(fd, USBDEVFS_RESET, 0)
-    os.close(fd)
+    try:
+        fcntl.ioctl(fd, USBDEVFS_RESET, 0)
+    finally:
+        os.close(fd)
 
 
 def reset_teensy():

diff --git a/usb_reset.py b/usb_reset.py
@@ -1,12 +1,32 @@
+"""
+    Example code for resetting the USB port that a Teensy microcontroller is
+    attached to. There are a lot of situations where a Teensy or Arduino can
+    end up in a bad state and need resetting, this code is useful for 
+"""
+
 import os
 import fcntl
 import subprocess
 
 
+# Equivalent of the _IO('U', 20) constant in the linux kernel.
 USBDEVFS_RESET = ord('U') << (4*2) | 20
 
 
 def get_teensy():
+    """
+        Gets the devfs path to a Teensy microcontroller by scraping the output
+        of the lsusb command
+        
+        The lsusb command outputs a list of USB devices attached to a computer
+        in the format:
+            Bus 002 Device 009: ID 16c0:0483 Van Ooijen Technische Informatica Teensyduino Serial
+        The devfs path to these devices is:
+            /dev/bus/usb/<busnum>/<devnum>
+        So for the above device, it would be:
+            /dev/bus/usb/002/009
+        This function generates that path.
+    """
     proc = subprocess.Popen(['lsusb'], stdout=subprocess.PIPE)
     out = proc.communicate()[0]
     lines = out.split('\n')
@@ -19,10 +39,19 @@ def get_teensy():
 
 
 def send_reset(dev_path):
+    """
+        Sends the USBDEVFS_RESET IOCTL to a USB device.
+        
+        dev_path - The devfs path to the USB device (under /dev/bus/usb/)
+                   See get_teensy for example of how to obtain this.
+    """
     fd = os.open(dev_path, os.O_WRONLY)
     fcntl.ioctl(fd, USBDEVFS_RESET, 0)
     os.close(fd)
 
 
 def reset_teensy():
-    send_reset(get_teensy())
+    """
+        Finds a teensy and reset it.
+    """
+    send_reset(get_teensy())
diff --git a/usb_reset.py b/usb_reset.py
@@ -0,0 +1,28 @@
+import os
+import fcntl
+import subprocess
+
+
+USBDEVFS_RESET = ord('U') << (4*2) | 20
+
+
+def get_teensy():
+    proc = subprocess.Popen(['lsusb'], stdout=subprocess.PIPE)
+    out = proc.communicate()[0]
+    lines = out.split('\n')
+    for line in lines:
+        if 'Teensyduino' in line:
+            parts = line.split()
+            bus = parts[1]
+            dev = parts[3][:3]
+            return '/dev/bus/usb/%s/%s' % (bus, dev)
+
+
+def send_reset(dev_path):
+    fd = os.open(dev_path, os.O_WRONLY)
+    fcntl.ioctl(fd, USBDEVFS_RESET, 0)
+    os.close(fd)
+
+
+def reset_teensy():
+    send_reset(get_teensy())